Recent data from cosmic ray experiments such as PAMELA, Fermi, ATIC and PPB-BETS all suggest the need for a new primary source of electrons and positrons at high (>~100 GeV) energies. Many proposals have been put forth to explain these data, usually relying on a single particle to annihilate or decay to produce e+e-. In this paper, we consider models with multiple species of WIMPs with significantly different masses. We show if such dark matter candidates chi_i annihilate into light bosons, they naturally produce equal annihilation rates, even as the available numbers of pairs for annihilation n_chi_i^2 differ by orders of magnitude. We argue that a consequence of these models can be to add additional signal naturally at lower (~100 GeV) versus higher (~ TeV) energies, changing the expected spectrum and even adding bumps at lower energies, which may alleviate some of the tension in the required annihilation rates between PAMELA and Fermi. These spectral changes may yield observable consequences in the microwave Haze signal observed at the upcoming Planck satellite. Such a model can connect to other observable signals such as DAMA and INTEGRAL by having the lighter (heavier) state be a pseudo-Dirac fermion with splitting 100 keV (1 MeV). We show that variations in the halo velocity dispersion can alleviate constraints from final state radiation in the galactic center and galactic ridge. If the lighter WIMP has a large self-interaction cross section, the light-WIMP halo might collapse, dramatically altering expectations for direct and indirect detection signatures.
We constrain the cosmological density of cosmic string loops using two observational signatures -- gravitational microlensing and the Kaiser-Stebbins effect. Photometry from RXTE and CoRoT space missions and pulsar timing from Parkes Pulsar Timing Array, Arecibo and Green Bank radio telescopes allow us to probe cosmic strings in a wide range of tensions $G\mu/c^2=10^{-16}\div10^{-10}$. We find that pulsar timing data provide the most stringent constraints on the abundance of light strings at the level $\Omega_s \sim 10^{-3}$. Future observational facilities such as the Square Kilometer Array will allow one to improve these constraints by orders of magnitude.
We introduce and publicly release a new code, ADAPTSMOOTH, which serves to smooth astronomical images in an adaptive fashion, in order to enhance the signal-to-noise ratio (S/N). The adaptive smoothing scheme allows to take full advantage of the spatially resolved photometric information contained in an image in that at any location the minimal smoothing is applied to reach the requested S/N. Support is given to match more images on the same smoothing length, such that proper estimates of local colours can be done, with a big potential impact on multi-wavelength studies of extended sources (galaxies, nebulae). Different modes to estimate local S/N are provided. In addition to classical arithmetic-mean averaging mode, the code can operate in median averaging mode, resulting in a significant enhancement of the final image quality and very accurate flux conservation. To this goal also other code options are implemented and discussed in this paper. Finally, we analyze in great detail the effect of the adaptive smoothing on galaxy photometry, in particular in terms of surface brightness (SB) profiles and aperture photometry: deviations in SB with respect to the original image can be limited to <0.01 mag, with flux difference in apertures of less than 0.001 mag.
We consider the application of quantum corrections computed using renormalization group arguments in the astrophysical domain and show that, for the most natural interpretation of the renormalization group scale parameter, if the gravitational coupling parameter $G$ varies as $10^{-7}$ of its value across a galaxy (which is roughly a variation of $10^{-12}$ per light-year), it is sufficient to generate galaxy rotation curves in agreement with the observations. The quality of the resulting fit is similar to the usual Isothermal profile quality once both the shape of the rotation curve and the mass-to-light ratios are considered for evaluation. In order to perform the analysis, we use recent high quality data from nine regular disk galaxies. For the sake of comparison, the same set of data is modeled also for the Modified Newtonian Dynamics (MOND) and for the recently proposed Scalar Tensor Vector Gravity (STVG). At face value, the model based on quantum corrections clearly leads to better fits than these two alternative theories.
The type 1/2 dichotomy in active galactic nuclei as well as direct interferometric observations at infrared wavelengths require a geometrically and optically thick clumpy dust torus. The mechanism to achieve this geometrical thickness is so far unclear. We propose a turbulence toy model where the cloud elasticity is due to the infrared radiation pressure between the clouds. Clouds with a velocity below a certain critical velocity, which we derive analytically, may therefore not collide directly, but will be pushed apart by the repulsive radiation force. Restricting our attention to regions in the interior of the torus, we show that a system of such clouds should have an equilibrium state with an rms-velocity of the same order but smaller than the critical velocity in order to obtain a torus scale height compatible with observations. We compare the range of allowed cloud parameters for our toy model to the literature and find that, while we cannot identify any one set of parameters that fits best to our model, slight modifications of that parameters produce clouds with rms-velocities >100 km/s due to the radiation forces. We derive a relation between the accretion rate through the torus and our model parameters, and demonstrate that the model is compatible with reasonable accretion rates for active galaxies. In order to get both, a reasonable accretion through the torus, and a sufficiently high rms-velocity for the required vertical scale height, one requires optically thick clouds with densities of order 10^-18 g/cm^3 and sizes of about 10^-4 pc < R < 10^-3 pc ...
Weak gravitational lensing has been used extensively in the past decade to constrain the masses of galaxy clusters, and is the most promising observational technique for providing the mass calibration necessary for precision cosmology with clusters. There are several challenges in estimating cluster masses, particularly (a) the sensitivity to astrophysical effects and observational systematics that modify the signal relative to the theoretical expectations, and (b) biases that can arise due to assumptions in the mass estimation method, such as the assumed radial profile of the cluster. All of these challenges are more problematic in the inner regions of the cluster, suggesting that their influence would ideally be suppressed for the purpose of mass estimation. However, at any given radius the differential surface density measured by lensing is sensitive to all mass within that radius, and the corrupted signal from the inner parts is spread out to all scales. We develop a new statistic that is ideal for estimation of cluster masses because it completely eliminates mass contributions below a chosen scale (which we suggest should be about 20 per cent of the virial radius), and thus reduces sensitivity to systematic and astrophysical effects. We use simulated and analytical profiles to quantify systematic biases on the estimated masses for several standard methods of mass estimation, finding that these can lead to significant mass biases that range from ten to over fifty per cent. The mass uncertainties when using our new statistic are reduced by up to a factor of ten relative to the standard methods, while only moderately increasing the statistical errors. This new method of mass estimation will enable a higher level of precision in future science work with weak lensing mass estimates for galaxy clusters.
The clustering of matter on cosmological scales is an essential probe for studying the physical origin and composition of our Universe. To date, most of the direct studies have focused on shear-shear weak lensing correlations, but it is also possible to extract the dark matter clustering by combining galaxy-clustering and galaxy-galaxy-lensing measurements. In this study we develop a method that can constrain the dark matter correlation function from galaxy clustering and galaxy-galaxy-lensing measurements, by focusing on the correlation coefficient between the galaxy and matter overdensity fields. To generate a mock galaxy catalogue for testing purposes, we use the Halo Occupation Distribution approach applied to a large ensemble of N-body simulations to model pre-existing SDSS Luminous Red Galaxy sample observations. Using this mock catalogue, we show that a direct comparison between the excess surface mass density measured by lensing and its corresponding galaxy clustering quantity is not optimal. We develop a new statistic that suppresses the small-scale contributions to these observations and show that this new statistic leads to a cross-correlation coefficient that is within a few percent of unity down to 5 Mpc/h. Furthermore, the residual incoherence between the galaxy and matter fields can be explained using a theoretical model for scale-dependent bias, giving us a final estimator that is unbiased to within 1%. We also perform a comprehensive study of other physical effects that can affect the analysis, such as redshift space distortions and differences in radial windows between galaxy clustering and weak lensing observations. We apply the method to a range of cosmological models and show the viability of our new statistic to distinguish between cosmological models.
Employing Eggleton's stellar evolution code with an optically thick wind assumption, we have systematically studied the WD + He star channel of Type Ia supernovae (SNe Ia), in which a carbon-oxygen WD accretes material from a He main-sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. We mapped out the parameter spaces for producing SNe Ia. According to a detailed binary population synthesis approach, we find that the Galactic SN Ia birthrate from this channel is $\sim$$0.3\times 10^{-3} {\rm yr}^{-1}$, and that this channel can produce SNe Ia with short delay times ($\sim45-$140 Myr). We also find that the surviving companion stars in this channel have a high spatial velocity ($>$400 km/s) after SN explosion, which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708.
The final composition of giant planets formed as a result of gravitational instability in the disk gas depends on their ability to capture solid material (planetesimals) during their 'pre-collapse' stage, when they are extended and cold, and contracting quasi-statically. The duration of the pre-collapse stage is inversely proportional roughly to the square of the planetary mass, so massive protoplanets have shorter pre-collapse timescales and therefore limited opportunity for planetesimal capture. The available accretion time for protoplanets with masses of 3, 5, 7, and 10 Jupiter masses is found to be 7.82E4, 2.62E4, 1.17E4 and 5.67E3 years, respectively. The total mass that can be captured by the protoplanets depends on the planetary mass, planetesimal size, the radial distance of the protoplanet from the parent star, and the local solid surface density. We consider three radial distances, 24, 38, and 68 AU, similar to the radial distances of the planets in the system HR 8799, and estimate the mass of heavy elements that can be accreted. We find that for the planetary masses usually adopted for the HR 8799 system, the amount of heavy elements accreted by the planets is small, leaving them with nearly stellar compositions.
We present CCD BV and JHK$_{s}$ 2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting magnitude of $V\sim19$ mag. The star count method shows that the centre of the cluster lies at $\alpha_{2000}=04^{h}09^{m}36^{s}$, $\delta_{2000}=49^{\circ}28^{'}43^{''}$ and its angular size is $r=10$ arcmin. The optical and near-infrared two-colour diagrams reveal the colour excesses in the direction of the cluster as $E(B-V)=0.68\pm0.06$, $E(J-H)=0.21\pm0.02$ and $E(J-K_{s})=0.33\pm0.04$ mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age Main-Sequences (ZAMS) provided an average distance modulus of $(m-M)_{0}=10.80\pm0.13$ mag, which can be translated into a distance of $1440\pm80$ pc. Finally, using Padova isochrones we determined the metallicity and age of the cluster as $Z=0.015\pm 0.004$ ($[M/H]=-0.10 \pm 0.10$ dex) and $\log (t/yr) = 8.40\pm0.04$, respectively.
We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80 UMa). The companion has M-band ($\lambda$ = 4.8 $\mu$m) magnitude 8.8 and projected separation 1".11 (28 AU) from Alcor. The companion is most likely a low-mass ($\sim$0.3 \msun) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L$_{\rm X}$ $\simeq$ 10$^{28.3}$ erg/s). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d $\simeq$ 25 pc, age $\simeq$ 0.5 Gyr), and has been occasionally mentioned as a possible distant (709") companion of the stellar quadruple Mizar ($\zeta$ UMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for other UMa nuclear members shows that Alcor has a peculiar velocity of 1.1 km/s, which is comparable to the predicted velocity amplitude induced by the newly-discovered companion ($\sim$1 km/s). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 $\pm$ 0.19 pc (74 $\pm$ 39 kAU; minimum 18 kAU), and their velocity vectors are marginally consistent ($\chi^2$ probability 6%). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the 2nd closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d $<$ 40 pc).
We present a summary of an asteroseismic signature of helium ionization reported by Houdek & Gough (2007, 2008, 2009) for low-degree p modes in solar-type stars, and illustrate its applications for asteroseismic diagnoses.
By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole moments J2 and J4 were computed using a solar model obtained from CESAM stellar evolution code (Morel, 1997) combined with a recent model of solar differential rotation deduced from helioseismology (Corbard et al., 2002). This model takes into account a near-surface radial gradient of rotation which was inferred and quantified from MDI f-mode observations by Corbard and Thompson (2002). The effect of this observational near-surface gradient on the theoretical values of the surface parameters J2, J4 is investigated. The results show that the octopole moment J4 is much more sensitive than the quadrupole moment J2 to the subsurface radial gradient of rotation.
The Planck On-Fligh Forecaster (POFF) is a tool to predict when a position in the sky will be within a selected angular distance from any receiver direction of the Planck satellite according to its pre-programmed observational strategy. This tool has been developed in the framework of the Planck LFI Core Team activities, but it is now used by the whole collaboration. In this paper we will describe the tool and its applications to plan observations with other instruments of point sources which are expected to enhance the possibilities of scientific exploitation of the Planck satellite data, once they will be publicly available. Collecting simultaneous multi-frequency data, like those that can be planned with the POFF, will help, on one hand, to investigate variability of point sources and, on the other, to reconstruct point source spectral energy distributions on wide frequency ranges minimizing the effects due to source variability. POFF is a combination of IDL routines which combine the publicly available information about the Planck scanning strategy and focal plane shape in order to identify if a given (list of) position(s) can be observable by the satellite at a given frequency and/or by selected receivers in a given time range. The output can be displayed with the desired time resolution and selecting among various sorting options. The code is not a Planck product, but it has been validated within the Planck LFI pipeline. The code format and the large number of options make it flexible and suitable for many applications, allowing to get results quickly. POFF is currently successfully used to plan activities within the Planck collaboration, including observations with several ground-based facilities, and it is distributed outside it.
Realistic 3D radiative MHD simulations reveal the magneto-convective processes underlying the formation of the photospheric fine structure of sunspots, including penumbral filaments and umbral dots. Here we provide results from a statistical analysis of simulated umbral dots and compare them with reports from high-resolution observations. A multi-level segmentation and tracking algorithm has been used to isolate the bright structures in synthetic bolometric and continuum brightness images. Areas, brightness, and lifetimes of the resulting set of umbral dots are found to be correlated: larger umbral dots tend to be brighter and live longer. The magnetic field strength and velocity structure of umbral dots on surfaces of constant optical depth in the continuum at 630 nm indicate that the strong field reduction and high velocities in the upper parts of the upflow plumes underlying umbral dots are largely hidden from spectro-polarimetric observations. The properties of the simulated umbral dots are generally consistent with the results of recent high-resolution observations. However, the observed population of small, short-lived umbral dots is not reproduced by the simulations, possibly owing to insufficient spatial resolution.
The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. [ABRIDGED] We perform a detailed elemental abundance analysis based on equivalent width measurements from high-resolution spectra that were obtained while Bulge dwarf stars were optically magnified during microlensing events. [ABRIDGED] We present detailed elemental abundances and stellar ages for six new dwarf stars in the Galactic bulge. Combining these with previous events, which we have re-analysed using the same methods, we study a homogeneous sample of 15 microlensed dwarf and subgiant stars in the Bulge, which constitute the largest sample to date of microlensed dwarf stars in the Galactic bulge. The stars span the full range of metallicities from [Fe/H]=-0.72 to +0.54, and their average metallicity is <[Fe/H]>=-0.08\pm 0.47, close to the average metallicity based on giant stars in the Bulge. Furthermore, the stars follow well-defined abundance trends, that for [Fe/H]<0 coincide with those of the Galactic thick disc. This suggests that the Bulge and the thick disc have had, at least partially, similar chemical histories. At sub-solar metallicities we find consistently old ages, while at super-solar metallicities we find a wide range of ages. Using the new age and abundance results from the microlensed dwarf stars we investigate possible formation scenarios for the Bulge.
We study a sample of 16 microlensed Galactic bulge main sequence turnoff region stars for which high dispersion spectra have been obtained with detailed abundance analyses. We demonstrate that there is a very strong and highly statistically significant correlation between the maximum magnification of the microlensed bulge star and the value of the [Fe/H] deduced from the high resolution spectrum of each object. Physics demands that this correlation, assuming it to be real, be the result of some sample bias. We suggest several possible explanations, but are forced to reject them all,and are left puzzled. To obtain a reliable metallicity distribution in the Galactic bulge based on microlensed dwarf stars it will be necessary to resolve this issue through the course of additional observations.
We report measurements of the thermal emission of the young and massive planet CoRoT-2b at 4.5 and 8 microns with the Spitzer Infrared Array Camera (IRAC). Our measured occultation depths are 0.510 +- 0.042 % and 0.41 +- 0.11 % at 4.5 and 8 microns, respectively. In addition to the CoRoT optical measurements, these planet/star flux ratios indicate a poor heat distribution to the night side of the planet and are in better agreement with an atmosphere free of temperature inversion layer. Still, the presence of such an inversion is not definitely ruled out by the observations and a larger wavelength coverage is required to remove the current ambiguity. Our global analysis of CoRoT, Spitzer and ground-based data confirms the large mass and size of the planet with slightly revised values (Mp = 3.47 +- 0.22 Mjup, Rp = 1.466 +- 0.044 Rjup). We find a small but significant offset in the timing of the occultation when compared to a purely circular orbital solution, leading to e cos(omega) = -0.00291 +- 0.00063 where e is the orbital eccentricity and omega is the argument of periastron. Constraining the age of the system to be at most of a few hundreds of Myr and assuming that the non-zero orbital eccentricity is not due to a third undetected body, we model the coupled orbital-tidal evolution of the system with various tidal Q values, core sizes and initial orbital parameters. For log(Q_s') = 5 - 6, our modelling is able to explain the large radius of CoRoT-2b if log(Q_p') <= 5.5 through a transient tidal circularization and corresponding planet tidal heating event. Under this model, the planet will reach its Roche limit within 20 Myr at most.
The dynamics of prominence fine structures is a challenge to understand the formation of cool plasma prominence embedded in the hot corona. Recent observations from the high resolution Hinode/SOT telescope allow us to compute velocities perpendicularly to the line-of-sight or transverse velocities. Combining simultaneous observations obtained in H-alpha with Hinode/SOT and the MSDP spectrograph operating in the Meudon solar tower we derive the velocity vectors of a quiescent prominence. The velocities perpendicular to the line-of-sight are measured by time slice technique, the Dopplershifts by the bisector method. The Dopplershifts of bright threads derived from the MSDP reach 15 km/s at the edges of the prominence and are between +/- 5 km/s in the center of the prominence. Even though they are minimum values due to seeing effect, they are of the same order as the transverse velocities. These measurements are very important because they suggest that the verticalstructures shown in SOT may not be real vertical magnetic structures in the sky plane. The vertical structures could be a pile up of dips in more or less horizontal magnetic field lines in a 3D perspective, as it was proposed by many MHD modelers. In our analysis we also calibrate the Hinode H-alpha data using MSDP observations obtained simultaneously.
The INFN and INAF Italian research institutes developed a space-borne X-Ray polarimetry experiment based on a X-Ray telescope, focussing the radiation on a Gas Pixel Detector (GPD). The instrument obtains the polarization angle of the absorbed photons from the direction of emission of the photoelectrons as visualized in the GPD. Here we will show how we compute the angular resolution of such an instrument.
The recent observation by the PAMELA satellite of a rising positron fraction up to $\sim$ 100 GeV has triggered a considerable amount of putative interpretations in terms of dark matter (DM) annihilation or decay. Here, we make a critical reassessment of such a possibility, recalling the elementary conditions with respect to the standard astrophysical background that would make it likely, showing that they are not fulfilled. Likewise, we argue that, as now well accepted, DM would need somewhat contrived properties to contribute significantly to the observed positron signal, even when including e.g. clumpiness effects. This means that most of natural DM candidates arising in particle physics beyond the standard model are not expected to be observed in the cosmic antimatter spectrum, unfortunately. However, this does not prevent them from remaining excellent DM candidates, this only points towards the crucial need of developing much more complex detection strategies (multimessenger, multiwavelength, multiscale searches).
As a test of the standard inflationary cosmology, which generically predicts nearly scale-invariant spectrum of primordial curvature fluctuations, we perform Markov-Chain Monte-Carlo analysis to search for possible modulations in the power spectrum and determine its shape together with the cosmological parameters using cosmic microwave background radiation data. By incorporating various three-parameter features on the simple power-law spectrum, we find an oscillatory modulation localized around the comoving wavenumber $k\simeq 0.009\mathrm{Mpc}^{-1}$ at 99.995% confidence level which improves the log-likelihood as much as $-\Delta 2\ln {\cal L}\equiv \Delta \chi^2_{\rm eff}=-22$. This feature can be detected even if we use only the cross correlation between the temperature and the E-mode polarization anisotropies.
The SuperAGILE (SA) instrument is a X-ray detector for As- trophysics measurements, part of the Italian AGILE satellite for X-Ray and Gamma-Ray Astronomy launched at 23/04/2007 from India. SuperAGILE is now studying the sky in the 18 - 60 KeV energy band. It is detecting sources with advanced imaging and timing detection and good spectral detection capabilities. Several astrophysical sources has been detected and localized, including Crab, Vela and GX 301-2. The instrument has the skill to resolve correctly sources in a field of view of [-40, +40] degrees interval, with the angular resolution of 6 arcmin, and a spectral analysis with the resolution of 8 keV. Transient events are regularly detected by SA with the aid of its temporal resolution (2 microsec- onds) and using signal coincidence on different portions of the instrument, with confirmation from other observatories. The SA data processing scientic software performing at the AGILE Ground Segment is divided in modules, grouped in a processing pipeline named SASOA. The processing steps can be summarized in data reduction, photonlist building, sources extraction and sources analysis. The software services allow orbital data processing (near real-time), daily data set integration, Temporal Data Set (TDS) processing and TDS processing with source target optimization (TDS SRC). Automatic data processing monitoring and interactive data analysis is possible from an internet connected worksta- tion, with the use of SA data processing Web services. Many solutions were implemented in order to achieve fault tolerance. Archive management and data storage are performed with the help of relational database instruments.
Low-luminosity galaxies are known to outnumber the bright galaxy population
in poor groups and clusters of galaxies. Yet, the investigation of
low-luminosity galaxy populations outside the Local Group remains rare and the
dependence on different group environments is still poorly understood. Previous
investigations revealed photometric scaling relations for early-type dwarfs and
a strong dependence of morphology with environment.
The present study aims to analyse the photometric and spectroscopic
properties of the low-luminosity galaxy population in the nearby, well-evolved
and early-type dominated NGC 5846 group of galaxies. It is the third most
massive aggregate of early-type galaxies after the Virgo and Fornax clusters in
the local universe. Photometric scaling relations and the distribution of
morphological types as well as the characteristics of emission-line galaxies
are investigated.
Spectroscopically selected low-luminosity group members from the Sloan
Digital Sky Survey with cz<3000 km/s within a radius of 2 deg=0.91 Mpc around
NGC 5846 are analysed. Surface brightness profiles of early-type galaxies are
fit by a Sersic model r^(1/n). Star formation rates, oxygen abundances and
emission characteristics are determined for emission-line galaxies. [abridged]
Properties of candidate stars, forming out of molecular clouds, depend on the ambient conditions of the parent cloud. We present a series of 2D and 3D simulations of fragmentation of molecular clouds in starburst regions as well as clouds under conditions in dwarf galaxies, leading to the formation of protostellar cores. We explore in particular the metallicity dependence of molecular cloud fragmentation and the possible variations in the dense core mass function, as the expression of a multi-phase ISM, due to dynamic and thermodynamic effects in starburst and metal-poor environments. To study the level of fragmentation during the collapse, the adaptive mesh refinement code FLASH is used. With this code, including self-gravity, thermal balance, turbulence and shocks, collapse is simulated with four different metallicity dependent cooling functions. Turbulent and rotational energies are considered as well. During the simulations, number densities of 10^8-10^9 cm^-3 are reached. The influences of dust and cosmic ray heating are investigated and a comparison to isothermal cases is made. The presented results indicate that fragmentation increases with metallicity, while cosmic ray and gas-grain collisional heating counteract this. We also find that modest rotation and turbulence can impact the cloud evolution as far as fragmentation is concerned. In this light, we conclude that radiative feedback, in starburst regions, will inhibit fragmentation, while low-metallicity dwarfs also should enjoy a star formation mode in which fragmentation is suppressed.
New astrophysical instruments such as skA (square kilometer Array) and IXO (formerly Constellation X) promise the discovery of tens of thousands of new isolated rotating neutron stars (pulsars), neutron stars in low-mass X-ray binaries (LMXBs), anomalous X-ray pulsars (AXPs), and soft gamma repeaters (SGRs). Many of these neutron stars will experience dramatic density changes over their active lifetimes, driven by either stellar spin-up or spin-down, which may trigger phase transitions in their dense baryonic cores. More than that, accretion of matter onto neutron stars in LMXBs is believed to cause pycno-nuclear fusion reactions in the inner crusts of neutron stars. The associated reaction rates may be drastically altered if strange quark matter would be absolutely stable. This paper outlines the investigative steps that need to be performed in order to explore the thermal response of neutron stars to rotationally-driven phase transitions in their cores as well as to nuclear burning scenarios in their crusts. Such research complements the exploration of the phase diagram of dense baryonic matter through particle collider experiments, as performed at RHIC in the USA and as planned at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany.
The search for life outside of the Solar System should not be restricted to exclusively planetary bodies; large moons of extrasolar planets may also be common habitable environments throughout the Galaxy. Extrasolar moons, or exomoons, may be detected through transit timing effects induced onto the host planet as a result of mutual gravitational interaction. In particular, transit timing variations (TTV) and transit duration variations (TDV) are predicted to produce a unique exomoon signature, which is not only easily distinguished from other gravitational perturbations, but also provides both the period and mass of an exomoon. Using these timing effects, photometry greater or equal to that of the Kepler Mission is readily able to detect habitable-zone exomoons down to 0.2 Earth masses and could survey up to 25,000 stars for 1 Earth-mass satellites. We discuss future possibilities for spectral retrieval of such bodies and show that transmission spectroscopy with JWST should be able to detect molecular species with ~30 transit events, in the best cases.
We unify inflation and dark matter via a single scalar field phi. One of the main difficulties for this unification is that between inflation and dark matter one needs a successful reheating process and a long lasting period of radiation. Therefore the amount of energy density in the inflaton-dark matter field phi must be fine tune after reheating to give dark matter. Here we show an alternative scheme in which the inflaton decays completely, disappearing entirely from the spectrum. However, at low energies, before matter-radiation equality, the same interaction term that leads to the inflaton decay, regenerates phi. An essential feature is that the transition between the intermediate radiation dominated to the dark matter phase is related to a quantum generation of the scalar field \phi instead to purely classical dynamics. Thanks to this quantum transition the inflation-dark matter unification can take place naturally without fine tuning. The unification scheme presented here has three parameters, the mass of the dark matter particle m_o, the inflation parameter lambda and the coupling g for the inflaton interaction. Phenomenology fixes the value for lambda and gives a constraint between g and m_o, leaving only the mass of the dark matter particle m_o as a free parameter. These same three parameters lambda, m_o, g are present in models with inflation and a dark matter wimp particle but without unification. Therefore our unification scheme does not increase the number of parameters and it accomplishes the desired unification between inflaton and dark matter for free.
We present a detailed study of the collapse of a spherical perturbation in DGP braneworld gravity for the purpose of modeling simulation results for the halo mass function, bias and matter power spectrum. The presence of evolving modifications to the gravitational force in form of the scalar brane-bending mode lead to qualitative differences to the collapse in ordinary gravity. In particular, differences in the energetics of the collapse necessitate a new, generalized method for defining the virial radius which does not rely on strict energy conservation. These differences and techniques apply to smooth dark energy models with w unequal -1 as well. We also discuss the impact of the exterior of the perturbation on collapse quantities due to the lack of a Birkhoff theorem in DGP. The resulting predictions for the mass function, halo bias and power spectrum are in good overall agreement with DGP N-body simulations on both the self-accelerating and normal branch. In particular, the impact of the Vainshtein mechanism as measured in the full simulations is matched well. The model and techniques introduced here can serve as a practical tool for placing consistent constraints on braneworld models using observations of large scale structure.
We investigate constraints on power spectra of the primordial curvature and tensor perturbations with priors based on single-field slow-roll inflation models. We stochastically draw the Hubble slow-roll parameters and generate the primordial power spectra using the inflationary flow equations. Using data from recent observations of CMB and several measurements of geometrical distances in the late Universe, Bayesian parameter estimation and model selection are performed for models that have separate priors on the slow-roll parameters. The same analysis is also performed adopting the standard parameterization of the primordial power spectra. We confirmed that the scale-invariant Harrison-Zel'dovich spectrum is disfavored with increased significance from previous studies. While current observations appear to be optimally modeled with some simple models of single-field slow-roll inflation, data is not enough constraining to distinguish these models.
We describe a novel GaAs/AlGaAs double-quantum-well device for the infrared photon detection, called Charge-Sensitive Infrared Phototransistor (CSIP). The principle of CSIP detector is the photo-excitation of an intersubband transition in a QW as an charge integrating gate and the signal amplification by another QW as a channel with very high gain, which provides us with extremely high responsivity (10^4 -- 10^6 A/W). It has been demonstrated that the CSIP designed for the mid-infrared wavelength (14.7 um) has an excellent sensitivity; the noise equivalent power (NEP) of 7x10^-19 W/rHz with the quantum efficiency of ~2%. Advantages of the CSIP against the other highly sensitive detectors are, huge dynamic range of >10^6, low output impedance of 10^3 -- 10^4 Ohms, and relatively high operation temperature (>2K). We discuss possible applications of the CSIP to FIR photon detection covering 35 -- 60 um waveband, which is a gap uncovered with presently available photoconductors.
We demonstrate the capability of AKARI for mapping diffuse far-infrared emission and achieved reliability of all-sky diffuse map. We have conducted an all-sky survey for more than 94 % of the whole sky during cold phase of AKARI observation in 2006 Feb. -- 2007 Aug. The survey in far-infrared waveband covers 50 um -- 180 um with four bands centered at 65 um, 90 um, 140 um, and 160 um and spatial resolution of 3000 -- 4000 (FWHM).This survey has allowed us to make a revolutionary improvement compared to the IRAS survey that was conducted in 1983 in both spatial resolution and sensitivity after more than a quarter of a century. Additionally, it will provide us the first all-sky survey data with high-spatial resolution beyond 100 um. Considering its extreme importance of the AKARI far-infrared diffuse emission map, we are now investigating carefully the quality of the data for possible release of the archival data. Critical subjects in making image of diffuse emission from detected signal are the transient response and long-term stability of the far-infrared detectors. Quantitative evaluation of these characteristics is the key to achieve sensitivity comparable to or better than that for point sources (< 20 -- 95 [MJy/sr]). We describe current activities and progress that are focused on making high quality all-sky survey images of the diffuse far-infrared emission.
We describe the current status and the prospect for the development of monolithic Ge:Ga array detector for SAFARI. Our goal is to develop a 64x64 array for the 45 -- 110 um band, on the basis of existing technologies to make 3x20 monolithic arrays for the AKARI satellite. For the AKARI detector we have achieved a responsivity of 10 A/W and a read-out noise limited NEP (noise equivalent power) of 10^-17 W/rHz. We plan to develop the detector for SAFARI with technical improvements; significantly reduced read-out noise with newly developed cold read-out electronics, mitigated spectral fringes as well as optical cross-talks with a multi-layer antireflection coat. Since most of the elemental technologies to fabricate the detector are flight-proven, high technical readiness levels (TRLs) should be achieved for fabricating the detector with the above mentioned technical demonstrations. We demonstrate some of these elemental technologies showing results of measurements for test coatings and prototype arrays.
(abridged) Uninhibited radiative cooling in clusters of galaxies would lead to excessive mass accretion rates contrary to observations. One of the key proposals to offset radiative energy losses is thermal conduction from outer, hotter layers of cool core clusters to their centers. However, conduction is sensitive to magnetic field topology. In cool-core clusters the heat buoyancy instability (HBI) leads to B-fields ordered preferentially in the direction perpendicular to that of gravity, which significantly reduces the level of conduction below the classical Spitzer-Braginskii value. However, the cluster cool cores are rarely in perfect hydrostatic equilibrium. Sloshing motions due to minor mergers, galaxy motions or AGN can significantly perturb the gas and affect the level of thermal conduction. We perform 3D AMR MHD simulations of the effect of turbulence on the properties of the anisotropic thermal conduction in cool core clusters. We show that very weak subsonic motions, well within observational constraints, can randomize the magnetic field and significantly boost effective thermal conduction beyond the saturated values expected in the pure unperturbed HBI case. We find that the turbulent motions can essentially restore the conductive heat flow to the cool core to level comparable to the theoretical maximum of 1/3 Spitzer for a highly tangled field. Remarkably, runs with radiative cooling show that the cooling catastrophe can be averted and the cluster core stabilized. Above a critical Froude number, these same turbulent motions also eliminate the tangential bias in the velocity and magnetic field that is otherwise induced by the trapped g-modes. Our results can be tested with future radio polarization measurements, and have implications for efficient metal dispersal in clusters.
Total energy arguments (e.g., Fabian et al. 2002) suggest that black holes need to have masses significantly in excess of the prediction from the classic black hole mass - velocity dispersion relation (M-sigma) in order to offset the cooling losses in massive cool core clusters. This suggests that the black holes may be too small to power such clusters. However, Lauer et al. (2007) argue that the black hole mass - bulge luminosity relationship is a better predictor of black hole masses in high luminosity galaxies and that this relationship predicts significantly higher masses in BCGs. They find slow increase in the velocity dispersion with luminosity and a more rapid increase in effective radii with luminosity seen in BCGs as opposed to less luminous galaxies. Motivated by these results and the theoretical work of Boylan-Kolchin et al. (2006) on isolated mergers, we perform high-resolution cosmological simulations of dry mergers in a massive galaxy cluster identified in the Millennium Run including both the dark matter halos and stellar bulges of merging galaxies. We demonstrate that the BCG clearly evolves away from the size-luminosity relation as defined by the smaller galaxies (i.e., the relation bends) and we also see a bending in the luminosity-sigma relation. As black hole mass is expected to be proportional to the mass and luminosity of the stellar bulge of the BCGs (if they were formed in predominantly dissipationless mergers), our findings are consistent with those of Lauer et al. (2007) on a qualitative level and suggest that the black holes in BCGs may indeed be more massive than predicted from the standard M-sigma relation.
The nearby ($z=0.03015$) cluster of galaxies Abell~2199 was observed by Suzaku in X-rays, with five pointings for $\sim 20$ ks each. From the XIS data, the temperature and metal abundance profiles were derived out to $\sim 700$ kpc (0.4 times virial radius). Both these quantities decrease gradually from the center to peripheries by a factor of $\sim 2$, while the oxygen abundance tends to be flat. The temperature within 12' ($\sim 430$ kpc) is $\sim 4$ keV, and the 0.5--10 keV X-ray luminosity integrated up to 30' is $(2.9 \pm 0.1) \times 10^{44}$ erg s$^{-1}$, in agreement with previous XMM-Newton measurements. Above this thermal emission, no significant excess was found either in the XIS range below $\sim 1$ keV, or in the HXD-PIN range above $\sim 15$ keV. The 90%-confidence upper limit on the emission measure of an assumed 0.2 keV warm gas is (3.7--7.5) $\times 10^{62}$ cm$^{-3}$ arcmin$^{-2}$, which is 3.7--7.6 times tighter than the detection reported with XMM-Newton. The 90%-confidence upper limit on the 20--80 keV luminosity of any power law component is $1.8 \times 10^{43}$ erg s$^{-1}$, assuming a photon index of 2.0. Although this upper limit does not reject the possible 2.1$\sigma$ detection by the BeppoSAX PDS, it is a factor of 2.1 tighter than that of the PDS if both are considered upper limits. The non-detection of the hard excess can be reconciled with the upper limit on diffuse radio emission, without invoking the very low magnetic fields ($< 0.073 \mu$G) which were suggested previously.
The International Pulsar Timing Array project combines observations of pulsars from both Northern and Southern hemisphere observatories with the main aim of detecting ultra-low frequency (~10^-9 to 10^-8 Hz) gravitational waves. Here we introduce the project, review the methods used to search for gravitational waves emitted from coalescing supermassive binary black-hole systems in the centres of merging galaxies and discuss the status of the project.
Recent observations of the black hole (BH) - bulge scaling relations usually report positive redshift evolution, with higher redshift galaxies harboring more massive BHs than expected from the local relations. All of these studies focus on broad line quasars with BH mass estimated from virial estimators based on single-epoch spectra. Since the sample selection is largely based on quasar luminosity, the cosmic scatter in the BH-bulge relation introduces a statistical bias leading to on average more massive BHs given galaxy properties at high redshift (Lauer et al. 2007). We here emphasize a previously under-appreciated statistical bias resulting from the uncertainty of single-epoch virial BH mass estimators and the shape of the underlying (true) BH mass function, which leads to on average overestimation of the true BH masses at the high-mass end (Shen et al. 2008). We demonstrate that the latter virial mass bias can contribute a substantial amount to the observed excess in BH mass at fixed bulge properties, comparable to the Lauer et al. bias. The virial mass bias is independent of the Lauer et al. bias, hence if both biases are at work, they can largely (or even fully) account for the observed BH mass excess at high redshift.
A model is presented for generation of fast solar wind in coronal holes, relying on heating that is dominated by turbulent dissipation of MHD fluctuations transported upwards in the solar atmosphere. Scale-separated transport equations include large-scale fields, transverse Alfvenic fluctuations, and a small compressive dissipation due to parallel shears near the transition region. The model accounts for proton temperature, density, wind speed, and fluctuation amplitude as observed in remote sensing and in situ satellite data.
We discovered multiple high-velocity (ranging from -900 to -650 km/s) and narrow (FWHM = 15 km/s) absorption components corresponding to both the D2 and the D1 lines of Na I on a high dispersion spectrum of V1280 Sco observed on 2009 May 9 (UT), 814 d after the V-band maximum. Subsequent observations carried out on 2009 June and July confirmed at least 11 distinct absorption components in both systems. Some components had deepened during the two months period while their HWHMs and wavelengths remained nearly constant. We suggest these high velocity components originate in cool clumpy gas clouds moving on the line of sight, produced in interactions between pre-existing cool circumstellar gas and high velocity gas ejected in the nova explosion. The optical region spectrum of V1280 Sco in 2009 is dominated by the continuum radiation and exhibits no forbidden line characterizing the nebular phase of typical novae. Permitted Fe II lines show doubly peaked emission profiles and some strong Fe II lines are accompanied by a blue shifted (about -255 km/s) absorption component. However, no high-velocity and narrow components corresponding to those of Na I could be detected in Fe II lines nor in the Balmer lines. The 255 km/s low velocity absorption component is most probably originating in the wind from the nova.
In recent years we have been witnessing the discovery of one extrasolar gas giant after another. Now the time has come to detect more low-mass planets like Super-Earths and Earth-like objects. An interesting question to ask is: where should we look for them? We have explored here the possibility of finding Super-Earths in the close vicinity of gas giants, as a result of the early evolution of planetary systems. For this purpose, we have considered a young planetary system containing a Super-Earth and a gas giant, both embedded in a protoplanetary disc. We have shown that, if the Super-Earth is on the internal orbit relative to the gas giant, the planets can easily become locked in a mean motion resonance. This is no longer true, however, if the Super-Earth is on the external orbit. In this case we have obtained that the low-mass planet is captured in a trap at the outer edge of the gap opened by the giant planet and no first order mean motion commensurabilities are expected. Our investigations might be particularly useful for the observational TTV (Transit Timing Variation) technique.
I introduce an algorithm for estimating parameters from multidimensional data based on forward modelling. In contrast to many machine learning approaches it avoids fitting an inverse model and the problems associated with this. The algorithm makes explicit use of the sensitivities of the data to the parameters, with the goal of better treating parameters which only have a weak impact on the data. The forward modelling approach provides uncertainty (full covariance) estimates in the predicted parameters as well as a goodness-of-fit for observations. I demonstrate the algorithm, ILIUM, with the estimation of stellar astrophysical parameters (APs) from simulations of the low resolution spectrophotometry to be obtained by Gaia. The AP accuracy is competitive with that obtained by a support vector machine. For example, for zero extinction stars covering a wide range of metallicity, surface gravity and temperature, ILIUM can estimate Teff to an accuracy of 0.3% at G=15 and to 4% for (lower signal-to-noise ratio) spectra at G=20. [Fe/H] and logg can be estimated to accuracies of 0.1-0.4dex for stars with G<=18.5. If extinction varies a priori over a wide range (Av=0-10mag), then Teff and Av can be estimated quite accurately (3-4% and 0.1-0.2mag respectively at G=15), but there is a strong and ubiquitous degeneracy in these parameters which limits our ability to estimate either accurately at faint magnitudes. Using the forward model we can map these degeneracies (in advance), and thus provide a complete probability distribution over solutions. (Abridged)
Observations of the (N_J=1_1-1_0) ground state transition of O_2 with the Odin satellite resulted in a about 5 sigma detection toward the dense core rho Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam width of 10', larger than the size of the dense core, so that the precise nature of the emitting source and its exact location and extent are unknown. The current investigation is intended to remedy this. Telluric absorption makes ground based O_2 observations essentially impossible and observations had to be done from space. mm-wave telescopes on space platforms were necessarily small, which resulted in large, several arcminutes wide, beam patterns. Although the Earth's atmosphere is entirely opaque to low-lying O_2 transitions, it allows ground based observations of the much rarer O18O in favourable conditions and at much higher angular resolution with larger telescopes. In addition, rho Oph A exhibits both multiple radial velocity systems and considerable velocity gradients. Extensive mapping of the region in the proxy C18O (J=3-2) line can be expected to help identify the O_2 source on the basis of its line shape and Doppler velocity. Line opacities were determined from observations of optically thin 13C18O (J=3-2) at selected positions. During several observing periods, two C18O intensity maxima in rho Oph A were searched for in the 16O18O (2_1-0_1) line at 234 GHz with the 12m APEX telescope. Our observations resulted in an upper limit on the integrated O18O intensity of < 0.01 K km/s (3 sigma) into the 26.5" beam. We conclude that the source of observed O_2 emission is most likely confined to the central regions of the rho Oph A cloud. In this limited area, implied O_2 abundances could thus be higher than previously reported, by up to two orders of magnitude.
The X-ray emission of GRBs observed by \emph{Swift} has the exponential functional form in the prompt phase and relaxes to a power-law decay at time $T_p$. We explore the correlation between $T_p$ and the X-ray luminosity of GRBs at $T_p$ and find a luminosity relation which holds for GRBs with $T_p/(1+z) \gtrsim 2 \mathrm{s}$. A fit to the luminosity relation gives its intrinsic scatter at $0.77 \pm 0.11$. Some implications of the luminosity relation are discussed, especially on the time duration of GRBs and their classification.
In this review, I present our current state of knowledge regarding both Classical Nova and Recurrent Nova systems. Two particular objects (V1974 Cyg and RS Oph) are chosen to illustrate the range of phenomena that may be associated with their outbursts. The wider importance of nova research is emphasised and some of the most pressing unsolved problems are summarised.
We present the results of the two most recent (2005) XMM-Newton observations of Saturn together with the re-analysis of an earlier (2002) observation from the XMM-Newton archive and of three Chandra observations in 2003 and 2004. While the XMM-Newton telescope resolution does not enable us to resolve spatially the contributions of the planet's disk and rings to the X-ray flux, we can estimate their strengths and their evolution over the years from spectral analysis, and compare them with those observed with Chandra. The spectrum of the X-ray emission is well fitted by an optically thin coronal model with an average temperature of 0.5 keV. The addition of a fluorescent oxygen emission line at ~0.53 keV improves the fits significantly. In accordance with earlier reports, we interpret the coronal component as emission from the planetary disk, produced by the scattering of solar X-rays in Saturn's upper atmosphere, and the line as originating from the Saturnian rings. The strength of the disk X-ray emission is seen to decrease over the period 2002 - 2005, following the decay of solar activity towards the current minimum in the solar cycle. By comparing the relative fluxes of the disk X-ray emission and the oxygen line, we suggest that the line strength does not vary over the years in the same fashion as the disk flux. We consider possible alternatives for the origin of the line. The connection between solar activity and the strength of Saturn's disk X-ray emission is investigated and compared with that of Jupiter. We also discuss the apparent lack of X-ray aurorae on Saturn and conclude that they are likely to lie below the sensitivity threshold of current Earth-bound observatories. A similar comparison for Uranus and Neptune leads to the same disappointing conclusion.
Aims: Caustic-crossing binary-lens microlensing events are important anomalous events, because they may reveal an extrasolar planet companion orbiting the lens star. Fast and robust modelling methods are thus of prime interest to quickly conclude on the possible planetary nature of the event. Cassan (2008) introduced a new set of parameters to model binary-lens events, which are closely related to the features observed in the light curve. In this work, we explain how Bayesian priors can be added in this framework, and investigate on possible interesting choices. Methods: We develop a mathematical formulation that allows to compute analytically priors on the new parameters, given some prior knowledge on other physical quantities. We explicitely compute the priors for a number of interesting cases, and show how this can be implemented in a fully Bayesian, Markov-Chain Monte-Carlo algorithm. Results: Using Bayesian priors can speed up microlens fitting codes by reducing time spent on physically implausible models, and helps to discriminate among alternative models based on the physical plausibility of their parameters.
We present a new upper limit of \sum m_{\nu} < 0.28 (95% CL) on the sum of the neutrino masses assuming a flat LCDM cosmology. This bound is derived from a new photometric redshift catalogue of over 700,000 Luminous Red Galaxies (MegaZ-LRG DR7) with a volume of 3.3 (Gpc/h)^3, extending over the redshift range 0.45 < z < 0.65 and up to angular scales of l_{max} = 300. The data are combined with 5-year WMAP CMB temperature and polarisation fluctuations, Baryon Acoustic Oscillations (BAO), type 1a Supernovae (SNe) and an HST prior on the Hubble parameter. This is the first combined constraint from a photometric redshift catalogue with other cosmological probes. When combined with WMAP this data set proves to be as constraining as the addition of all SNe and BAO data available to date. The upper limit is one of the tightest and `cleanest' constraints on the neutrino mass from cosmology.
The influence of rotation on the properties of red giants is studied in the context of the asteroseismic modelling of these stars. While red giants exhibit low surface rotational velocities, we find that the rotational history of the star has a large impact on its properties during the red giant phase. In particular, for stars massive enough to ignite He burning in non-degenerate conditions, rotational mixing induces a significant increase of the stellar luminosity and shifts the location of the core helium burning phase to a higher luminosity in the HR diagram. This of course results in a change of the seismic properties of red giants at the same evolutionary state. As a consequence the inclusion of rotation significantly changes the fundamental parameters of a red giant star as determined by performing an asteroseismic calibration. In particular rotation decreases the derived stellar mass and increases the age. Depending on the rotation law assumed in the convective envelope and on the initial velocity of the star, non-negligible values of rotational splitting can be reached, which may complicate the observation and identification of non-radial oscillation modes for red giants exhibiting moderate surface rotational velocities. By comparing the effects of rotation and overshooting, we find that the main-sequence widening and the increase of the H-burning lifetime induced by rotation (Vini=150 km/s) are well reproduced by non-rotating models with an overshooting parameter of 0.1, while the increase of luminosity during the post-main sequence evolution is better reproduced by non-rotating models with overshooting parameters twice as large. This is due to the fact that rotation not only increases the size of the convective core but also changes the chemical composition of the radiative zone.
The damped and sub-damped Lyman-alpha absorption line systems in quasar spectra are believed to be produced by intervening galaxies. However, the connection of quasar absorbers to galaxies is not well-understood, since attempts to image the absorbing galaxies have often failed. While most DLAs appear to be metal-poor, a population of metal-rich absorbers, mostly sub-DLAs, has been discovered in recent studies. Here we report high-resolution K-band imaging with the Keck Laser Guide Star Adaptive Optics (LGSAO) system of the field of quasar SDSSJ1323-0021 in search of the galaxy producing the z = 0.72 sub-DLA absorber. With a metallicity of 2-4 times the solar level, this absorber is of the most metal-rich systems found to date. Our data show a large bright galaxy with an angular separation of only 1.25" from the quasar, well-resolved from the quasar at the high resolution of our data. The galaxy has a magnitude of K = 17.6-17.9, which corresponds to a luminosity of ~ 3-6 L*. Morphologically, the galaxy is fit with a model with an effective radius, enclosing half the total light, of R_e = 4 kpc and a bulge-to-total ratio of 0.4-1.0, indicating a substantial bulge stellar population. Based on the mass-metallicity relation of nearby galaxies, the absorber galaxy appears to have a stellar mass > 10^{11} M_sun. Given the small impact parameter, this massive galaxy appears to be responsible for the metal-rich sub-DLA. The absorber galaxy is consistent with the metallicity-luminosity relation observed for nearby galaxies, but is near the upper end of metallicity. Our study marks the first application of LGSAO for study of structure of galaxies producing distant quasar absorbers. Finally, this study offers the first example of a massive galaxy with a substantial bulge producing a metal-rich absorber.
We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with gamma-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and gamma-ray emission in star-forming galaxies.
A large class of the dynamical laws for causal sets described by a classical process of sequential growth yield a cyclic universe, whose cycles of expansion and contraction are punctuated by single `origin elements' of the causal set. We present evidence that the effective dynamics of the immediate future of one of these origin elements, within the context of the sequential growth dynamics, yields an initial period of de Sitter like exponential expansion, and argue that the resulting picture has many attractive features as a model of the early universe, with the potential to solve some of the standard model puzzles without any fine tuning.
We consider a gravitational theory of a scalar field $\phi$ with nonminimal derivative coupling to curvature. The coupling terms have the form $\kappa_1 R\phi_{,\mu}\phi^{,\mu}$ and $\kappa_2 R_{\mu\nu}\phi^{,\mu}\phi^{,\nu}$ where $\kappa_1$ and $\kappa_2$ are coupling parameters with dimensions of length-squared. In general, field equations of the theory contain third derivatives of $g_{\mu\nu}$ and $\phi$. However, in the case $-2\kappa_1=\kappa_2\equiv\kappa$ the derivative coupling term reads $\kappa G_{\mu\nu}\phi^{,mu}\phi^{,\nu}$ and the order of corresponding field equations is reduced up to second one. Assuming $-2\kappa_1=\kappa_2$, we study the spatially-flat Friedman-Robertson-Walker model with a scale factor $a(t)$ and find new exact cosmological solutions. It is shown that properties of the model at early stages crucially depends on the sign of $\kappa$. For negative $\kappa$ the model has an initial cosmological singularity, i.e. $a(t)\sim (t-t_i)^{2/3}$ in the limit $t\to t_i$; and for positive $\kappa$ the universe at early stages has the quasi-de Sitter behavior, i.e. $a(t)\sim e^{Ht}$ in the limit $t\to-\infty$, where $H=(3\sqrt{\kappa})^{-1}$. The corresponding scalar field $\phi$ is exponentially growing at $t\to-\infty$, i.e. $\phi(t)\sim e^{-t/\sqrt{\kappa}}$. At late stages the universe evolution does not depend on $\kappa$ at all; namely, for any $\kappa$ one has $a(t)\sim t^{1/3}$ at $t\to\infty$. Summarizing, we conclude that a cosmological model with nonminimal derivative coupling of the form $\kappa G_{\mu\nu}\phi^{,mu}\phi^{,\nu}$ is able to explain in a unique manner both a quasi-de Sitter phase and an exit from it without any fine-tuned potential.
A dispersion equation, which describes the interaction of low density electron beam with a degenerate electron quantum plasma, is derived and examined for some interesting cases. In addition to the instabilities similar to those for classical plasma, due to the quantum effect a new type of instability is found. Growth rates of these new modes, which are purely quantum, are obtained. Furthermore, the excitation of Bogolyubov's type of spectrum by a strong electric field is discussed.
We have predicted theoretically and detected in laboratory experiments a new type of particle clustering (tangling clustering of inertial particles) in a stably stratified turbulence with imposed mean vertical temperature gradient. In this stratified turbulence a spatial distribution of the mean particle number density is nonuniform due to the phenomenon of turbulent thermal diffusion, that results in formation of a gradient of the mean particle number density, \nabla N, and generation of fluctuations of the particle number density by tangling of the gradient, \nabla N, by velocity fluctuations. The mean temperature gradient, \nabla T, produces the temperature fluctuations by tangling of the gradient, \nabla T, by velocity fluctuations. These fluctuations increase the rate of formation of the particle clusters in small scales. In the laboratory stratified turbulence this tangling clustering is much more effective than a pure inertial clustering that has been observed in isothermal turbulence. In particular, in our experiments in oscillating grid isothermal turbulence in air without imposed mean temperature gradient, the inertial clustering is very weak for solid particles with the diameter 10 microns and Reynolds numbers Re =250. Our theoretical predictions are in a good agreement with the obtained experimental results.
Analytical and numerical results on equilibrium configurations of rotating fluid bodies within Einstein's theory of gravitation are reviewed. Particular emphasis is placed on continuous parametric transitions to black holes. In this connection the uniqueness of extremal Kerr black holes is discussed.
By using the Fermi satellite, a group of physicists discovers a new type of gamma-ray active nucleus
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Observations in sub-THz range of large solar flares revealed a mysterious spectral component raising with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission of flare-accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one) or different properties of emitting electrons and location or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well-known and new in this context and calculates a representative set of their spectra produced by a) free-free emission, b) gyrosynchrotron emission, c) synchrotron emission from relativistic positrons/electrons, d) diffusive radiation, and e) Cherenkov emission. We discuss possible role of the mechanisms in forming the sub-THz emission and emphasize diagnostics potential for flare diagnostics.
We present a set of ultra-large particle-mesh simulations of the LyA forest targeted at understanding the imprint of baryon acoustic oscillations (BAO) in the inter-galactic medium. We use 9 dark matter only simulations which can, for the first time, simultaneously resolve the Jeans scale of the intergalactic gas while covering the large volumes required to adequately sample the acoustic feature. Mock absorption spectra are generated using the fluctuating Gunn-Peterson approximation which have approximately correct flux probability density functions (PDFs) and small-scale power spectra. On larger scales there is clear evidence in the redshift space correlation function for an acoustic feature, which matches a linear theory template with constant bias. These spectra, which we make publicly available, can be used to test pipelines, plan future experiments and model various physical effects. As an illustration we discuss the basic properties of the acoustic signal in the forest, the scaling of errors with noise and source number density, modified statistics to treat mean flux evolution and misestimation, and non-gravitational sources such as fluctuations in the photo-ionizing background and temperature fluctuations due to HeII reionization.
We study the properties of SDSS galaxies with and without AGN detection as a function of the local and global environment. For the full SDSS sample, we find indications that the local galaxy density is the most efficient parameter to separate galaxy populations, but we also find that galaxies at fixed local density show some remaining variation of their properties as a function of the distance to the nearest cluster of galaxies (in a range of 0 to 10 cluster virial radii). These differences seem to become less significant if the galaxy samples are additionally constrained to be hosted by groups of similar total luminosity. In AGN host galaxies, the morphology-density relation is much less noticeable when compared to the behaviour of the full SDSS sample, indicating a lack of sensitivity to the host group mass during the AGN phase probably due to the higher typical luminosities of the AGN hosts. In order to interpret this result we analyse control AGN samples with matching distributions of redshifts, r-band luminosities, g-r colours, concentrations, local densities and host group luminosities. The control samples also show a similar small dependence on the local density, but their colours are bluer compared to the AGN hosts, particularly at low local densities. However, when the local density is held fixed and the distance to the closest cluster of galaxies is allowed to vary, AGN hosts close to clusters tend to be bluer than the control sample, indicating the need of higher availability of cold gas supply to maintain a detectable AGN activity in these environments. Consistent with this result, AGN in bright, low concentration hosts (i.e. disky morphologies) are bluer than galaxies in the control sample, in agreement with previous findings connecting the presence of discs to AGN activity. (Abridged)
[abridged] The properties of galaxies with the reddest observed R-K colors (Extremely Red Objects, EROs), including their apparent division into passive and obscured active objects, are a known challenge for models of galaxy formation. We produce mock catalogues by interfacing the predictions of the MORGANA model with the spectro-photometric + radiative transfer code GRASIL and IR template library to show that the model correctly reproduces number counts, redshift distributions and active fractions of R-K>5 sources. We test the robustness of our results against different dust attenuations and against the inclusion of TP-AGB stars in Simple Stellar Populations used to generate galaxy spectra, and find that the inclusion of TP-AGBs has a relevant effect, in that it allows to increase by a large factor the number of very red active objects at all color cuts. We find that EROs are not a peculiar class of galaxies: though the oldest and the most obscured galaxies have a higher probability of being selected, many EROs have intermediate properties, so the population does not show bimodal properties. We predict that criteria based on optical colors are a poor discriminant of ERO activity, while deep observations in the FIR are the most efficient way to constrain the SSFR of these objects; we give predictions for future Herschel observations. Finally, we test whether a simple evolutionary sequence for the formation of z=0 massive galaxies, going through a sub-mm-bright phase and then a ERO phase, are typical in this galaxy formation model. We find that this sequence holds for ~25 per cent of z=0 massive galaxies, while the model typically shows a more complex connection between sub-mm, ERO and massive galaxies. [abridged]
Correlations between the intrinsic shapes of galaxy pairs, and between the intrinsic shapes of galaxies and the large-scale density field, may be induced by tidal fields. These correlations, which have been detected at low redshifts (z<0.35) for bright red galaxies in the Sloan Digital Sky Survey (SDSS), and for which upper limits exist for blue galaxies at z~0.1, provide a window into galaxy formation and evolution, and are also an important contaminant for current and future weak lensing surveys. Measurements of these alignments at intermediate redshifts (z~0.6) that are more relevant for cosmic shear observations are very important for understanding the origin and redshift evolution of these alignments, and for minimising their impact on weak lensing measurements. We present the first such intermediate-redshift measurement for blue galaxies, using galaxy shape measurements from SDSS and spectroscopic redshifts from the WiggleZ Dark Energy Survey. Our null detection allows us to place upper limits on the contamination of weak lensing measurements by blue galaxy intrinsic alignments that, for the first time, do not require significant model-dependent extrapolation from the z~0.1 SDSS observations. Also, combining the SDSS and WiggleZ constraints gives us a long redshift baseline with which to constrain intrinsic alignment models and contamination of the cosmic shear power spectrum. Assuming that the alignments can be explained by linear alignment with the smoothed local density field, we find that a measurement of \sigma_8 in a blue-galaxy dominated, CFHTLS-like survey would be contaminated by at most +/-0.02 (95% confidence level, SDSS and WiggleZ) or +/-0.03 (WiggleZ alone) due to intrinsic alignments. [Abridged]
We present high-resolution, high-S/N spectra of an extremely metal- poor
giant star Boo-1137 in the "ultra-faint" dwarf spheroidal galaxy (dSph) Bootes
I (absolute magnitude Mv ~ -6.3). With [Fe/H] = -3.7, this the most metal-poor
star yet identified in an ultra-faint dSph.
Comparison of relative abundances, [X/Fe], for some 15 elements with those of
the extremely metal-poor giants of the Galactic halo shows Boo-1137 is "normal"
with respect to C and N, the odd-Z elements Na and Al, the Fe-peak elements,
and the n-capture elements Sr and Ba, in comparison with the bulk of the halo
with [Fe/H] < -3.0. The alpha- elements Mg, Si, Ca, and Ti are all higher by
Delta[X/Fe] ~ 0.2 than average halo values. Monte-Carlo analysis indicates
Delta[alpha/Fe] values this large are expected with probability ~ 0.02. The
abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution,
consistent with the wide internal spread in Fe abundances we reported earlier.
The similarity of most of the Boo-1137 relative abundances with respect to halo
values, and the fact that the alpha-elements are all offset by a similar small
amount from the halo averages, points to the same underlying galaxy-scale
stellar initial mass function, but that Boo-1137 likely originated in a
star-forming region where the abundances reflect either poor mixing of
supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or
both.
Radiative transfer and radiation hydrodynamics use the relativistic Boltzmann equation to describe the kinetics of photons. The six-dimensional time-dependent transfer equation is difficult to solve unless the problem is in equilibrium or highly symmetric. When the radiation field is smooth, it is natural to take angular moments of the transfer equation to reduce the degrees of freedom. However, low-order moment equations contain terms that depend on higher-order moments. To close the system of moment equations, approximations are made to truncate this hierarchy. Popular closures used in astrophysics include flux limited diffusion and the M_1 closure, which are rather ad hoc and do not necessarily to capture the correct physics. In this paper, we propose a new closure scheme for radiative transfer. We start from a different perspective and highlight the consistency of a fully relativistic formalism. By employing the fact that photons do not self-interact, we conclude that a physical closure should be linear in the high-order Landau-Lifshitz frame. We then derive a general framework to approximate radiative transfer to arbitrary order based on relativistic Grad's moment method. This framework goes beyond the grey approximation even though the moments are frequency integrated. Together with the requirement that photon transport is reference frame independent, we are able to reduce the equations to second order. Finally, we discuss the detail mathematical structure and physical properties of the derived closure schemes.
We present MMT/Megacam imaging of the Leo IV dwarf galaxy in order to investigate its structure and star formation history, and to search for signs of association with the recently discovered Leo V satellite. Based on parameterized fits, we find that Leo IV is round, with $\epsilon < 0.16$ and a half-light radius of $r_{h} \simeq 130$ pc. Additionally, we perform a thorough search for extended structures in the plane of the sky and along the line of sight. We rigorously derive our surface brightness detection limit by implanting fake structures into our catalog with stellar populations identical to that of Leo IV. We show that we are sensitive to stream-like structures with surface brightness $\mu_{r}\lesssim29.6$ mag arcsec$^{-2}$, and at this limit, we find no stellar bridge between Leo IV and the recently discovered, nearby satellite Leo V. Using the color magnitude fitting package StarFISH, we determine that Leo IV is predominantly old ($>12$ Gyr) and metal poor ($[Fe/H]\sim-2.3$), consistent with a single dominant metallicity, although we can not rule out a significant spread in this value. We derive a luminosity of $M_{V}=-5.7\pm0.3$. Studying both the spatial distribution and frequency of Leo IV's 'blue plume' stars reveals evidence for a young ($\sim$2 Gyr) stellar population which makes up $\sim$2% of its stellar mass. This sprinkling of star formation, only detectable in this deep study, highlights the need for further imaging of the new Milky Way satellites along with theoretical work on the expected, detailed properties of these possible 'reionization fossils'.
There is a growing body of evidence for the presence of multiple stellar populations in some globular clusters, including NGC 1851. For most of these peculiar globular clusters, however, the evidence for the multiple red giant-branches (RGBs) having different heavy elemental abundances as observed in Omega Centauri is hitherto lacking, although spreads in some lighter elements are reported. It is therefore not clear whether they also share the suggested dwarf galaxy origin of Omega Cen or not. Here we show from the CTIO 4m UVI photometry of the globular cluster NGC 1851 that its RGB is clearly split into two in the U - I color. The two distinct RGB populations are also clearly separated in the abundance of heavy elements as traced by Calcium, suggesting that the type II supernovae enrichment is also responsible, in addition to the pollutions of lighter elements by intermediate mass asymptotic giant branch stars or fast-rotating massive stars. The RGB split, however, is not shown in the V - I color, as indicated by previous observations. Our stellar population models show that this and the presence of bimodal horizontal-branch distribution in NGC 1851 can be naturally reproduced if the metal-rich second generation stars are also enhanced in helium.
In the tidal disruption of a star by a black hole, roughly half of the stellar mass becomes bound and falls into the black hole, while the other half is ejected at high velocity. Several previous studies have considered the emission resulting from the accretion of bound material; we consider the possibility that the unbound debris may also radiate once it has expanded and become transparent. We show that the gradual energy input from hydrogen recombination compensates for adiabatic loses over significant expansion factors. The opacity also drops dramatically with recombination, and the internal energy can be radiated by means of a cooling-transparency wave propagating from the surface layers inward. The result is a brief optical transient occurring ~1 week after disruption and lasting 3-5 days with peak luminosities of 10^40-10^42 ergs/s, depending on the mass of the disrupted star. These recombination powered transients should accompany the x-ray/ultraviolet flare from the accretion of bound material, and so may be a useful signature for discriminating tidal disruption events, especially for lower and intermediate mass black holes.
We present a direct method for isolating the component of the starlight blocked by a planet as it transits its host star, and apply it to spectra of the bright transiting planet HD 189733b. We model the global shape of the stellar cross-correlation function as the convolution of a limb-darkened rotation profile and a gaussian representing the Doppler core of the average photospheric line profile. The light blocked by the planet during the transit is a gaussian of the same intrinsic width, whose trajectory across the line profile yields a precise measure of the misalignment angle and an independent measure of v sin I. We show that even when v sin I is less than the width of the intrinsic line profile, the travelling Doppler "shadow" cast by the planet creates an identifiable distortion in the line profiles which is amenable to direct modelling. Direct measurement of the trajectory of the missing starlight yields self-consistent measures of the projected stellar rotation rate, the intrinsic width of the mean local photospheric line profile, the projected spin-orbit misalignment angle, and the system's centre-of-mass velocity. Combined with the photometric rotation period, the results give a geometrical measure of the stellar radius which agrees closely with values obtained from high-precision transit photometry if a small amount of differential rotation is present in the stellar photosphere.
We consider cosmologies in which a dark-energy scalar field interacts with cold dark matter. The growth of perturbations is followed beyond the linear level by means of the time-renormalization-group method, which is extended to describe a multi-component matter sector. Even in the absence of the extra interaction, a scale-dependent bias is generated as a consequence of the different initial conditions for baryons and dark matter after decoupling. The effect is greatly enhanced by the extra coupling and can be at the percent level in the range of scales of baryonic acoustic oscillations. We compare our results with N-body simulations, finding very good agreement.
The formation of a solar system is believed to have followed a multi-stage process around a protostar. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag; there is a ``bottleneck'' at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Thus, successful planetary accretion requires rapid planetesimal growth to km scale. A commonly accepted picture is that for collisional velocities $V_c$ above a certain threshold collisional velocity, ${V_{th}} \sim$ 0.1-10 cm s$^{-1}$, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all collisions the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt explicitly with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter--phase diagrams, amorphs and polymorphs--has been neglected. Here it is demonstrated that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting or amphorph-/polymorphization and fusion to extend the collisional velocity range of primary accretion to $\Delta V_c \sim$ 1-100 m s$^{-1}$, which bound both turbulent RMS speeds and the velocity differences between boulder sized and small grains $\sim$ 1-50 m s$^{-1}$. Thus, as inspiraling meter sized bodies collide with smaller particles in this high velocity collisional fusion regime they grow rapidly to km scales and hence settle into Keplerian orbits in $\sim$ 10$^5$ years before stellar wind clears the disk of source material.
It has been argued recently by Copi etal (2009) that the lack of large angular correlations of the CMB temperature field provides strong evidence against the standard, statistically isotropic, inflationary LambdaCDM cosmology. We compare various estimators of the temperature correlation function showing how they depend on assumptions of statistical isotropy and how they perform on the WMAP 5 year ILC maps with and without a sky cut. We show that the low multipole harmonics that determine the large-scale features of the temperature correlation function can be reconstructed accurately, independent of any assumptions concerning statistical isotropy, from the data that lie outside the sky cuts. The temperature correlation functions computed from our reconstructions are in good agreement with those computed from the whole sky. A Bayesian analysis of the large-scale correlations is presented which shows that the data cannot exclude the standard LambdaCDM model. We discuss the differences between our conclusions and those of Copi et al.
A general equation of state is used to model unified dark matter and dark energy (dark fluid), and this model is equivalent to a single non-perfect fluid with bulk viscosity [Phys. Lett. B \textbf{633}, (2006) 1-8]. In this paper, we investigate scalar perturbation of this viscosity dark fluid model. For particular parameter selection, we find that perturbation quantity can be obtained exactly in the future university. We numerically solve the perturbation evolution equations, and compare the results with those of $\Lambda$CDM model. Gravitational potential and density perturbation of the model concerned here have the similar behavior with the standard model, though there exists significant value differences in the late universe.
We use the Novikov-Thorne thin disk model to fit the thermal continuum X-ray spectra of black hole X-ray binaries, and thereby extract the dimensionless spin parameter a* = a/M of the black hole as a parameter of the fit. We summarize the results obtained to date for six systems and describe work in progress on additional systems. We also describe recent methodological advances, our current efforts to make our analysis software fully available to others, and our theoretical efforts to validate the Novikov-Thorne model.
[Abridged] Superluminous Supernovae (SN2006gy, SN2005gj, SN2005ap, SN2008fz, SN2003ma) have been a challenge to explain by standard models. We present an alternative scenario involving a quark-nova (QN), an explosive transition of the newly born neutron star to a quark star in which a second explosion (delayed) occurs inside the already expanding ejecta of a normal SN. The reheated SN ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic expansion losses, unlike the standard SN case. Our model is successfully applied to SN2006gy, SN2005gj, SN2005ap, SN2008fz, SN2003ma with encouraging fits to the lightcurves. There are four predictions in our model: (i) superluminous SNe optical lightcurves should show a double-hump with the SN hump at weaker magnitudes occurring days to weeks before the QN; (ii) Two shock breakouts should be observed vis-a-vis one for a normal SN. Depending on the time delay, this would manifest as two distinct spikes in the X-ray region or a broadening of the first spike for extremely short delays; (iii) The QN deposits heavy elements of mass number A> 130 at the base of the preceeding SN ejecta. These QN r-processed elements should be visible in the late spectrum (few days-weeks in case of strong ejecta mixing) of the superluminous SN; (iv) The QN yield will also contain lighter elements (Hydrogen and Helium). We expect the late spectra to include H_alpha emission lines that should be distinct in their velocity signature from standard H_alpha emission.
FRIDA (inFRared Imager and Dissector for the Adaptative optics system of the GTC) will be a NIR (1-2.5microns) imager and Integral Field Unit spectrograph to operate with the Adaptative Optics system of the 10.4m GTC telescope. FRIDA will offer broad and narrow band diffraction-limited imaging and integral field spectroscopy at low, intermediate and high spectral resolution. The Extragalactic Astrophysics and Astronomical Instrumentation group of the Universidad Complutense de Madrid (GUAIX) is developing the Data Reduction Pipeline for FRIDA. Specific tools for converting output, reduced datacubes to the standard Euro3D FITS format will be developed, in order to allow users to exploit existing VO applications for analysis. FRIDA is to be commissioned on the telescope in 2011.
Many questions are still open regarding the structure and the dynamics of the solar core. By constraining more this region in the solar evolution models, we can reduce the incertitudes on some physical processes and on momentum transport mechanisms. A first big step was made with the detection of the signature of the dipole-gravity modes in the Sun, giving a hint of a faster rotation rate inside the core. A deeper analysis of the GOLF/SoHO data unveils the presence of a pattern of peaks that could be interpreted as dipole gravity modes. In that case, those modes can be characterized, thus bringing better constraints on the rotation of the core as well as some structural parameters such as the density at these very deep layers of the Sun interior.
We present the results of a search for new members of the Taurus star-forming region using data from the Spitzer Space Telescope and the XMM-Newton Observatory. We have obtained optical and near-infrared spectra of 44 sources that exhibit red Spitzer colors that are indicative of stars with circumstellar disks and 51 candidate young stars that were identified by Scelsi and coworkers using XMM-Newton. We also performed spectroscopy on four possible companions to members of Taurus that were reported by Kraus and Hillenbrand. Through these spectra, we have demonstrated the youth and membership of 41 sources, 10 of which were independently confirmed as young stars by Scelsi and coworkers. Five of the new Taurus members are likely to be brown dwarfs based on their late spectral types (>M6). One of the brown dwarfs has a spectral type of L0, making it the first known L-type member of Taurus and the least massive known member of the region (M=4-7 M_Jup). Another brown dwarf exhibits a flat infrared spectral energy distribution, which indicates that it could be in the protostellar class I stage (star+disk+envelope). Upon inspection of archival images from various observatories, we find that one of the new young stars has a large edge-on disk (r=2.5=350 AU). The scattered light from this disk has undergone significant variability on a time scale of days in optical images from the Canada-France-Hawaii Telescope. Using the updated census of Taurus, we have measured the initial mass function for the fields observed by XMM-Newton. The resulting mass function is similar to previous ones that we have reported for Taurus, showing a surplus of stars at spectral types of K7-M1 (0.6-0.8 M_sun) relative to other nearby star-forming regions like IC 348, Chamaeleon I, and the Orion Nebula Cluster.
We report results from tests of $^{83}$Kr$^{\mathrm{m}}$, as a calibration source in liquid argon and liquid neon. $^{83}$Kr$^{\mathrm{m}}$ atoms are produced in the decay of $^{83}$Rb, and a clear $^{83}$Kr$^{\mathrm{m}}$ scintillation peak at 41.5 keV appears in both liquids when filling our detector through a piece of zeolite coated with $^{83}$Rb. Based on this scintillation peak, we observe 6.0 photoelectrons/keV in liquid argon with a resolution of 6% ($\sigma$/E) and 3.0 photoelectrons/keV in liquid neon with a resolution of 19% ($\sigma$/E). The observed peak intensity subsequently decays with the $^{83}$Kr$^{\mathrm{m}}$ half-life after stopping the fill, and we find evidence that the spatial location of $^{83}$Kr$^{\mathrm{m}}$ atoms in the chamber can be resolved. $^{83}$Kr$^{\mathrm{m}}$ will be a useful calibration source for liquid argon and neon dark matter and solar neutrino detectors.
Recent measurements of the surface magnetic fields of classical T Tauri stars (CTTSs) and magnetic cataclysmic variables show that their magnetic fields have a complex structure. The magnetic field associated with the octupole moment may dominate the magnetic field associated with other moments in some stars, such as the CTTS V2129 Oph. Previously, we studied disc accretion onto stars with magnetic fields described by a superposition of aligned or misaligned dipole and quadrupole moments. In this paper, we present results of the first simulations of disc accretion onto stars with an \textit {octupole} field. As examples, we consider stars with a superposition of octupole and dipole fields of different strengths and investigate matter flow around them, the shapes of hot spots on their surfaces, and the light curves produced by their rotation. We investigate two possible mechanisms for producing phase shifts in the light curves of stars with complex fields: (1) change of the star's intrinsic magnetic field and (2) variation of the accretion rate, causing the disc to interact with the magnetic fields associated with different stellar magnetic moments. We also discuss the applicability of the potential approximation for extrapolation of the surface magnetic field to larger distances.
We have analyzed nearly all images of the Taurus star-forming region at 3.6-24um that were obtained during the cryogenic mission of the Spitzer Space Telescope (46 deg^2) and have measured photometry for all known members of the region that are within these data, corresponding to 348 sources. We have classified the members of Taurus according to whether they show evidence of disks and envelopes (classes I, II, and III). The disk fraction in Taurus is 75% for solar-mass stars and declines to 45% for low-mass stars and brown dwarfs (0.01-0.3 M_sun). This dependence on stellar mass is similar to that measured for Cha I, although the disk fraction in Taurus is slightly higher overall, probably because of its younger age (1 vs. 2-3 Myr). In comparison, the disk fraction for solar-mass stars is much lower (20%) in IC 348 and Sigma Ori, which are denser than Taurus and Cha I and are roughly coeval with the latter. These data indicate that disk lifetimes for solar-mass stars are longer in regions that have lower stellar densities. Through an analysis of multiple epochs of photometry that are available for ~200 Taurus members, we find that stars with disks exhibit significantly greater mid-IR variability than diskless stars. Finally, we have used our data in Taurus to refine the criteria for primordial, evolved, and transitional disks. The number ratio of evolved and transitional disks to primordial disks in Taurus is 15/98 for K5-M5, indicating a timescale of 0.15 x tau(primordial)=0.45 Myr for the clearing of the inner regions of optically thick disks. After applying the same criteria to older clusters (2-10 Myr), we find that the proportions of evolved and transitional disks in those populations are consistent with the measurements in Taurus when their star formation histories are properly taken into account. [Abridged]
We numerically investigate orbital evolution of star clusters (SCs) under the influence of dynamical friction by field stars of their host disk galaxies embedded in dark matter halos. We find that SCs with masses larger than 2 * 10^5 M_sun can show significant orbital decay within less than 1 Gyr due to dynamical friction by disk field stars in galaxies with disk masses M_d less than 10^9 M_sun. We also find that orbital decay of SCs due to dynamical friction is more remarkable in disk galaxies with smaller M_d and higher mass-ratios of disks to dark matter halos. The half-number radii R_h, sc and mean masses within R_h,sc of the SC systems (SCSs) in low-mass disk galaxies with M_d < 10^9 M_sun are found to evolve significantly with time owing to dynamical friction of SCs. More massive SCs that can spiral-in to the central regions of disks can form multiple SC systems with smaller velocity dispersions so that they can merge with one another to form single stellar nuclei with their masses comparable to ~0.4% of their host disk masses. Based on these results, we suggest that luminosity functions (LFs) for more massive globular clusters (GCs) with masses larger than 2 * 10^5 M_sun can steepen owing to transformation of the more massive GCs into single stellar nuclei through GC merging in less luminous galaxies. We also suggest that the half-number radii of GC systems can evolve owing to dynamical friction only for galaxies with their total masses smaller than ~ 10^{10} M_sun.
A new formulation of MOND as a modified-potential theory of gravity is propounded. In effect, the theory dictates that the MOND potential phi produced by a mass distribution rho is a solution of the Poisson equation for the modified source density rho*=-(1/4 pi G)divergence(g), where g=nu(|gN|/a0)gN, and gN is the Newtonian acceleration field of rho. This makes phi simply the scalar potential of the algebraic acceleration field g. The theory thus involves solving only linear differential equations, with one nonlinear, algebraic step. It is derivable from an action, satisfies all the usual conservation laws, and gives the correct center-of-mass acceleration to composite bodies. The theory is akin in some respects to the nonlinear Poisson formulation of Bekenstein and Milgrom, but it is different from it, and is obviously easier to apply. The two theories are shown to emerge as natural modifications of a Palatini-type formulation of Newtonian gravity, and are members in a larger class of bi-potential theories.
We present new brightness and magnetic images of the weak-line T Tauri star
V410 Tau, made using data from the NARVAL spectropolarimeter at Telescope
Bernard Lyot (TBL). The brightness image shows a large polar spot and
significant spot coverage at lower latitudes. The magnetic maps show a field
that is predominantly dipolar and non-axisymmetric with a strong azimuthal
component. The field is 50% poloidal and 50% toroidal, and there is very little
differential rotation apparent from the magnetic images.
A photometric monitoring campaign on this star has previously revealed V-band
variability of up to 0.6 magnitudes but in 2009 the lightcurve is much flatter.
The Doppler image presented here is consistent with this low variability.
Calculating the flux predicted by the mapped spot distribution gives an
peak-to-peak variability of 0.04 magnitudes. The reduction in the amplitude of
the lightcurve, compared with previous observations, appears to be related to a
change in the distribution of the spots, rather than the number or area.
This paper is the first from a Zeeman-Doppler imaging campaign being carried
out on V410 Tau between 2009-2012 at TBL. During this time it is expected that
the lightcurve will return to a high amplitude state, allowing us to ascertain
whether the photometric changes are accompanied by a change in the magnetic
field topology.
The spectral signatures of asymmetry in Type Ia Supernova (SN Ia) explosions are investigated, using a sample of late-time nebular spectra. First, a kinematical model is constructed for SN Ia 2003hv, which can account for the main features in its optical, Near-Infrared (NIR), and Mid-Infrared (Mid-IR) late-time spectra. It is found that an asymmetric off-center model can explain the observed characteristics of SN 2003hv. This model includes a relatively high density, Fe-rich region which displays a large velocity off-set, and a relatively low density, extended 56Ni-rich region which is more spherically distributed. The high density region consists of the inner stable Fe-Ni region and outer 56Ni-rich region. Such a distribution may be the result of a delayed-detonation explosion, in which the first deflagration produces the global asymmetry in the innermost ejecta, while the subsequent detonation can lead to the bulk spherical symmetry. This configuration, if viewed from the direction of the off-set, can consistently explain the blueshift in some of the emission lines and virtually no observed shift in other lines in SN 2003hv. For this model, we then explore the effects of different viewing angles and the implications for SNe Ia in general. The model predicts that a variation of the central wavelength, depending on the viewing angle, should be seen in some lines (e.g., [Ni II]7378), while the strongest lines (e.g., [Fe III] blend at 4700A) will not show this effect. By examining optical nebular spectra of 12 SNe Ia, we have found that such a variation indeed exists. We suggest that the global asymmetry in the innermost ejecta, as likely imprint of the deflagration flame propagation, is a generic feature of SNe Ia (abridged).
We present near-infrared imaging and spectroscopic high spatial resolution observations of the SMC region N88 containing the bright, excited, extincted and compact H II region N88A of size ~ 1 pc. To investigate its stellar content and reddening, N88 was observed using spectroscopy and imagery in the JHKs- and L'-band at a spatial resolution of ~ 0.1-0.3", using the VLT UT4 equipped with the NAOS adaptive optics system. In order to attempt to establish if the origin of the infra-red (IR) excess is due to bright nebulosity, circumstellar material and/or local dust, we used Ks vs J-K colour-magnitude (CM) and JHK colour-colour (CC) diagrams, as well as L' imagery.Our IR-data reveal in the N88 area an IR-excess fraction of geq 30 per cent of the detected stars,as well as an unprecedently detailed morphology of N88A. It consists of an embedded cluster of ~3.5" (~ 1 pc) in diameter, of at least thirteen resolved stars superposed with an unusual bright continuum centered on a very bright star. The four brightest stars in this cluster lie red-ward of H-K geq 0.45 mag, and could be classified as young stellar object (YSO) candidates. Four other probable YSO candidates are also detected in N88 along a south-north bow-shaped thin H2 filament at ~ 7" east of the young central bright star. At 0.2" east of this star, a heavily embedded core is detected that could be a massive class I protostar candidate. The 2.12 mu H2 image of N88A resembles a shell of diameter ~ 3" ~ 0.9 pc) centered on the bright star. The line ratios of H2 2-1 S(1) and 1-0 S(0) relative to 1-0 S(1), as well as the presence of high v lines, are indicative of photodissociation regions, rather than shocks.
(Abridged) From photometric observations of $\sim$ 47,000 stars and
spectroscopy of $\sim$ 11,000 stars, we describe the first extensive study of
the stellar population of the famous Double Cluster, h and $\chi$ Persei, down
to subsolar masses. Both clusters have E(B-V) $\sim$ 0.52--0.55 and dM =
11.8--11.85; the halo population, while more poorly constrained, likely has
identical properties. As determined from the main sequence turnoff, the
luminosity of M supergiants, and pre-main sequence isochrones, ages for h
Persei, $\chi$ Persei and the halo population all converge on $\approx$ 14 Myr.
From these data, we establish the first spectroscopic and photometric
membership lists of cluster stars down to early/mid M dwarfs. At minimum, there
are $\sim$ 5,000 members within 10' of the cluster centers, while the entire h
and $\chi$ Persei region has at least $\sim$ 13,000 and as many as 20,000
members. The Double Cluster contains $\approx$ 8,400 M$_{\odot}$ of stars
within 10' of the cluster centers. We estimate a total mass of at least 20,000
M$_{\odot}$. We conclude our study by outlining outstanding questions regarding
the properties of h and $\chi$ Persei. From comparing recent work, we compile a
list of intrinsic colors and derive a new effective temperature scale for O--M
dwarfs, giants, and supergiants.
The low order moments of the large scale peculiar velocity field are sensitive probes of the matter density fluctuations on very large scales. However, peculiar velocity surveys have varying spatial distributions of tracers, and so the moments estimated are hard to model and thus are not directly comparable between surveys. In addition, the sparseness of typical proper distance surveys can lead to aliasing of small scale power into what is meant to be a probe of the largest scales. Here we extend our previous optimization analysis of the bulk flow to include the shear and octupole moments where velocities are weighted to give an optimal estimate of the moments of an idealized survey, with the variance of the difference between the estimate and the actual flow being minimized. These "minimum variance" (MV) estimates can be designed to calculate the moments on a particular scale with minimal sensitivity to small scale power, and thus different surveys can be directly compared. The MV moments were also designed to have almost no correlations between them so that they are virtually orthogonal. Our estimate of the bulk flow on scales of ~ 100 Mpc/h has a magnitude of |v|= 416 +/- 78 km/s towards Galactic l = 282 degree +/- 11 degree and $b = 6 degree +/- 6 degree, in good agreement with our previous result found fitting only the bulk flow, but in disagreement with WMAP5 cosmological parameters at the 99.5% CL. The shear and octupole moments are consistent with WMAP5 power spectrum, but the measurement noise is larger for these moments than for the bulk flow. The relatively low shear moments suggest that the sources responsible for the bulk flow are at large distances.
Comet 133P/Elst-Pizarro is the first-known and currently best-characterised member of the main-belt comets, a recently-identified class of objects that exhibit cometary activity but which are dynamically indistinguishable from main-belt asteroids. We report here on the results of a multi-year monitoring campaign from 2003 to 2008, and present observations of the return of activity in 2007. We find a pattern of activity consistent with the seasonal activity modulation hypothesis proposed by Hsieh et al. (2004, AJ, 127, 2997). Additionally, recomputation of phase function parameters using data in which 133P was inactive yields new IAU parameters of H_R=15.49+/-0.05 mag and G_R=0.04+/-0.05, and linear parameters of m_R(1,1,0)=15.80+/-0.05 mag and Beta=0.041+/-0.005 mag/deg. Comparison between predicted magnitudes using these new parameters and the comet's actual brightnesses during its 2002 and 2007 active periods reveals the presence of unresolved coma during both episodes, on the order of ~0.20 of the nucleus cross-section in 2002 and ~0.25 in 2007. Multifilter observations during 133P's 2007 active outburst yield mean nucleus colours of B-V=0.65+/-0.03 mag, V-R=0.36+/-0.01 mag, and R-I=0.32+/-0.01 mag, with no indication of significant rotational variation, and similar colours for the trail. Finally, while 133P's trail appears shorter and weaker in 2007 than in 2002, other measures of activity strength such as dust velocity and coma contamination of nucleus photometry are found to remain approximately constant. We attribute changes in trail strength to the timing of observations and projection effects, thus finding no evidence of any substantial decrease in activity strength between 2002 and 2007.
We present the results from the first large 3.5mm polarimetric survey of radio loud active galactic nuclei (AGN). The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30m Telescope. Our sample, containing 146 sources, essentially consists of all known flat-radio-spectrum AGN with declination >-30 deg. (J2000.0) and flux density >~1Jy at ~86GHz, as measured at the IRAM 30m Telescope from 1978 to 1994. We detected linear and circular polarization (above 3 sigma levels of ~1.6%, and ~0.3%) for 76%, and 6% of the sample, respectively. We show a clear excess of the linear polarization degree detected at 86GHz with regard to that at 15GHz by a factor of ~2. Quasars and LBAS (LAT Bright AGN Sample) blazars in our sample show larger luminosity of their jets for lower linear polarization degree. Consistent with previous findings claiming larger Doppler factors for brighter gamma-ray blazars, LBAS blazars in our sample show larger luminosity than non detected ones in our sample, but we show that they are only quasars, and not BL Lac objects, which contribute to distribute LBAS blazars towards larger luminosities. We do not find a clear relation between the linear polarization angle and the jet structural position angle of any source class in our sample, that we interpret as a markedly non axisymmetric character of the 3mm emiting region in their jets. We find that intrinsic circular polarization is the most likely mechanism for generation of the circular polarization detected in our observations. Our new data are relevant, and can be used, to estimate the 3.5mm AGN contribution to linear polarization CMB measurements as those performed by the Planck satellite.
(Abridged) The hyperaccreting neutron star or magnetar disks cooled via neutrino emission can be a candidate of gamma-ray burst (GRB) central engines. The strong field $\geq10^{15}-10^{16}$ G of the magnetar can play a significant role in affecting the disk properties and even lead to the funnel accretion process. We investigate the effects of strong fields on the disks around magnetars, and discuss implications of such accreting magnetar systems for GRB and GRB-like events. We discuss quantum effects of the strong fields on the disk, and use the MHD conservation equations to describe the behavior of the disk flow coupled with a large scale field, which is generated by the star-disk interaction. In general, stronger fields give higher disk densities, pressures, temperatures and neutrino luminosity, and change the electron fraction and degeneracy state significantly. A magnetized disk is always viscously stable outside the Alfv\'{e}n radius, but will be thermally unstable near the Alfv\'{e}n radius where the magnetic field plays a more important role in transferring the angular momentum and heating the disk than the viscous stress. The funnel accretion process will be only important for an extremely strong field, which creates a magnetosphere inside the Alfv\'{e}n radius and truncates the plane disk. Because of higher temperature and more concentrated neutrino emission of the magnetar surface ring-like belt region covered by funnel accretion, the neutrino annihilation rate from the accreting magnetars can be much higher than that from accreting neutron stars without fields. Furthermore, the neutrino annihilation mechanism and the magnetically-driven pulsar wind from the magnetar surface can work together to generate and feed an ultra-relativistic jet along the stellar magnetic poles.
We report the first results of a research program to explore the sensitivity of the orbits of Oort cloud comets to changes in the strength of the Galactic tides in the plane of the disk and also to changes in the mass of the host star. We performed 2D simulations that confirm that the effects of the tides on comet orbits are sensitive to a star's distance from the Galactic center. A comet cloud closer to the Galactic center than the Sun will have comet perihelia reduced to the region of the inner planets more effectively by the planar tides alone. Similar results are found for a star of smaller mass. We also show how this phenomenon of comet injection persists for a set of alternative Galactic potential models. These preliminary results suggest a fruitful line of research, one that aims to generalize the study of comet cloud dynamics to systems different from the Solar System. In particular, it will allow us to study the roles played by comet clouds in defining the boundaries of the Galactic Habitable Zone.
The purpose of this review paper is to summarise the pulsar timing method, to provide an overview of recent research into the spin-down of pulsars over decadal timescales and to highlight the science that can be achieved using high-precision timing of millisecond pulsars.
On 2009 June 5, the Gamma-ray Burst Monitor (GBM) onboard the Fermi Gamma-ray Space Telescope triggered on two short, and relatively dim bursts with spectral properties similar to Soft Gamma Repeater (SGR) bursts. Independent localizations of the bursts by triangulation with the Konus-RF and with the Swift satellite, confirmed their origin from the same, previously unknown, source. The subsequent discovery of X-ray pulsations with the Rossi X-ray Timing Explorer (RXTE), confirmed the magnetar nature of the new source, SGR J0418+5729. We describe here the Fermi/GBM observations, the discovery and the localization of this new SGR, and our infrared and Chandra X-ray observations. We also present a detailed temporal and spectral study of the two GBM bursts. SGR J0418+5729 is the second source discovered in the same region of the sky in the last year, the other one being SGR J0501+4516. Both sources lie in the direction of the galactic anti-center and presumably at the nearby distance of ~2 kpc (assuming they reside in the Perseus arm of our galaxy). The near-threshold GBM detection of bursts from SGR J0418+5729 suggests that there may be more such dim SGRs throughout our galaxy, possibly exceeding the population of bright SGRs. Finally, using sample statistics, we conclude that the implications of the new SGR discovery on the number of observable active magnetars in our galaxy at any given time is <10, in agreement with our earlier estimates.
Recently the Fermi GBM and LAT Collaborations reported their new observational data disfavoring quite a number of the quantum gravity theories, including the one suggesting the nonlinear (logarithmic) modification of a quantum wave equation. We show that the latter is still far from being ruled out: it is not only able to explain the new data but also its phenomenological implications turn out to be more vast (and more interesting) than one expected before.
We investigate a series of steady-state models of galaxy clusters, in which the hot intracluster gas is efficiently heated by active galactic nucleus (AGN) feedback and thermal conduction, and in which the mass accretion rates are highly reduced compared to those predicted by the standard cooling flow models. We perform a global Lagrangian stability analysis. We show for the first time that the global radial instability in cool core clusters can be suppressed by the AGN feedback mechanism, provided that the feedback efficiency exceeds a critical lower limit. Furthermore, our analysis naturally shows that the clusters can exist in two distinct forms. Globally stable clusters are expected to have either: 1) cool cores stabilized by both AGN feedback and conduction, or 2) non-cool cores stabilized primarily by conduction. Intermediate central temperatures typically lead to globally unstable solutions. This bimodality is consistent with the recently observed anticorrelation between the flatness of the temperature profiles and the AGN activity (Dunn & Fabian 2008) and the observation by Rafferty et al. (2008) that the shorter central cooling times tend to correspond to significantly younger AGN X-ray cavities.
We use high-res cosmological hydro AMR simulations to predict the hydrogen Lalpha emission from the cold gas streams that fed galaxies in massive haloes at high z. The local emissivities due to collisional excitation are calculated from the simulated gas properties, while photoionization is less important. The Lalpha surface density is mapped assuming that 85% of the Lalpha photons are observed. Typical haloes of mass Mv~10^{12-13}Msun at z ~ 3 emit as Lalpha blobs (LABs) with luminosities 10^{43-44} erg/s and 50-100kpc extent. Most of the Lalpha comes from the extended, narrow, partly clumpy, inflowing, cold streams of (1-5)*10^4K that feed the galaxy. Dust absorption is negligible in the streams. The predicted LAB morphology is irregular, with dense clumps and elongated extensions. The area contained within isophotes with surface brightnesses of 2.2*10^{-18} erg s^{-1} cm^{-2} arcsec^{-2} is ~20-200 arcsec^2. The linewidth is expected to range from a few hundreds to above 1000 km/s with a large variance. The typical Lalpha surface brightness profile is proportional to r^{-1.2}. The Lalpha emission in our simulations is powered by the gravitational energy gained by the streaming into the halo potential well, while the UV background contributes <20%. A toy model of gravitational heating explains the simulated results. The simulated LABs are similar in luminosity, morphology and extent to the observed LABs, and they have distinct kinematic features. The predicted luminosity function is consistent with observations, and the predicted areas and linewidths reproduce the observed scaling relations. The LABs can be regarded as direct detections of the cold streams that drive galaxy evolution at high z. This mechanism for producing LABs appears inevitable in most high-z galaxies.
Since various structural components of planetary nebulae manifest themselves
differently, a combination of optical, infrared, submm, and radio techniques is
needed to derive a complete picture of planetary nebulae. The effects of
projection can also make the derivation of the true 3-D structure difficult.
Using a number of examples, we show that bipolar and multipolar nebulae are
much more common than usually inferred from morphological classifications of
apparent structures of planetary nebulae.
We put forward a new hypothesis that the bipolar and multipolar lobes of PN
are not regions of high-density ejected matter, but the result of ionization
and illumination. The visible bright regions are in fact volume of low
densities (cleared by high-velocity outflows) where the UV photons are being
channelled through. We suggest that multipolar nebulae with similar lobe sizes
are not caused by simultaneous ejection of matter in several directions, but by
leakage of UV photons into those directions.
We investigate strongly interacting dense matter and neutron stars using a flavor-SU(3) approach based on a non-linear realization of chiral symmetry as well as a hadronic flavor-SU(2) parity-doublet model. We study chiral symmetry restoration and the equation of state of stellar matter and determine neutron star properties using different sets of degrees of freedom. Finally, we include quarks in the model approach. We show the resulting phase diagram as well as hybrid star solutions for this model.
We report an indication (3.22 sigma) of ~ 1860 Hz quasi-periodic oscillations from a neutron star low-mass X-ray binary 4U 1636-536. If confirmed, this will be by far the highest frequency feature observed from an accreting neutron star system, and hence could be very useful to understand such systems. This plausible timing feature was observed simultaneously with lower (~ 585 Hz) and upper (~ 904 Hz) kilohertz quasi-periodic oscillations. The two kilohertz quasi-periodic oscillation frequencies had the ratio of ~ 1.5, and the frequency of the alleged ~ 1860 Hz feature was close to the triple and the double of these frequencies. This can be useful to constrain the models of all the three features. In particular, the ~ 1860 Hz feature could be (1) from a new and heretofore unknown class of quasi-periodic oscillations, or (2) the first observed overtone of lower or upper kilohertz quasi-periodic oscillations. Finally we note that, although the relatively low significance of the ~ 1860 Hz feature argues for caution, even a 3.22 sigma feature at such a uniquely high frequency should be interesting enough to spur a systematic search in the archival data, as well as to scientifically motivate sufficiently large timing instruments for the next generation X-ray missions.
We estimate the detection efficiency of binary gravitational lensing events through the channel of high-magnification events. From this estimation, we find that binaries in the separations ranges of 0.1 < s < 10, 0.2 < s < 5, and 0.3 < s < 3 can be detected with ~ 100% efficiency for events with magnifications higher than A=100, 50, and 10, respectively, where s represents the projected separation between the lens components normalized by the Einstein radius. We also find that the range of high efficiency covers nearly the whole mass-ratio range of stellar companions. Due to the high efficiency in wide ranges of parameter space, we point out that majority of binary-lens events will be detected through the high-magnification channel in lensing surveys that focus on high-magnification events for efficient detections of microlensing planets. In addition to the high efficiency, the simplicity of the efficiency estimation makes the sample of these binaries useful in the statistical studies of the distributions of binary companions as functions of mass ratio and separation. We also discuss other importance of these events.
The MAGIC experiment, a very large Imaging Air Cherenkov Telescope (IACT) with sensitivity to low energy (E < 100 GeV) VHE gamma rays, has been operated since 2004. It has been found that the gamma/hadron separation in IACTs becomes much more difficult below 100 GeV [Albert et al 2008] A system of two large telescopes may eventually be triggered by hadronic events containing Cherenkov light from only one electromagnetic subcascade or two gamma subcascades, which are products of the single pi^0 decay. This is a possible reason for the deterioration of the experiment's sensitivity below 100 GeV. In this paper a system of two MAGIC telescopes working in stereoscopic mode is studied using Monte Carlo simulations. The detected images have similar shapes to that of primary gamma-rays and they have small sizes (mainly below 400 photoelectrons (p.e.)) which correspond to an energy of primary gamma-rays below 100 GeV. The background from single or two electromagnetic subcascdes is concentrated at energies below 200 GeV. Finally the number of background events is compared to the number of VHE gamma-ray excess events from the Crab Nebula. The investigated background survives simple cuts for sizes below 250 p.e. and thus the experiment's sensitivity deteriorates at lower energies.
To improve the planet detection efficiency, current planetary microlensing experiments are focused on high-magnification events searching for planetary signals near the peak of lensing light curves. However, it is known that central perturbations can also be produced by binary companions and thus it is important to distinguish planetary signals from those induced by binary companions. In this paper, we analyze the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007-BLG-091, OGLE-2007-BLG-355/MOA-2007-BLG-278, and MOA-2007-BLG-199/OGLE-2007-BLG-419, for all of which exhibit short-term perturbations near the peaks of the light curves. From detailed modeling of the light curves, we find that the perturbations of the events are caused by binary companions rather than planets. From close examination of the light curves combined with the underlying physical geometry of the lens system obtained from modeling, we find that the short time-scale caustic-crossing feature occurring at a low or a moderate base magnification with an additional secondary perturbation is a typical feature of binary-lens events and thus can be used for the discrimination between the binary and planetary interpretations.
We present potential detections of H-band scattered light emission around four young star, selected from a total sample of 45 young stars observed with the CIAO coronagraph of the Subaru telescope. Two CTTS, CI Tau and DI Cep, and two WTTS, LkCa 14 and RXJ 0338.3+1020 were detected. In all four cases, the extended emission is within the area of the residual PSF halo, and is revealed only through careful data reduction. We compare the observed extended emission with simulations of the scattered light emission, to evaluate the plausibility and nature of the detected emission.
We study the impact of cosmic inhomogeneities on the interpretation of SNe observations. We build an inhomogeneous universe model that can confront supernova data and yet is reasonably well compatible with the Copernican Principle. Our model combines a relatively small local void, that gives apparent acceleration at low redshifts, with a meatball model that gives sizeable lensing (dimming) at high redshifts. Together these two elements, which focus on different effects of voids on the data, allow the model to mimic the concordance model.
The magnetic star HD 21699 possesses a unique magnetic field structure where the magnetic dipole is displaced from the centre by 0.4 +/- 0.1 of the stellar radius (perpendicularly to the magnetic axis), as a result, the magnetic poles are situated close to one another on the stellar surface with an angular separation of 55$^o$ and not 180$^o$ as seen in the case of a centred dipole. Respectively, the two magnetic poles form a large "magnetic spot". High-resolution spectra were obtained allowing He I and Si II abundance variations to be studied as a function of rotational phase. The results show that the helium abundance is concentrated in one hemisphere of the star, near the magnetic poles and it is comparatively weaker in another hemisphere, where magnetic field lines are horizontal with respect to the stellar surface. At the same time, the silicon abundance is greatest between longitudes of 180 - 320$^o$, the same place where the helium abundance is the weakest. These abundance variations (with rotational phase) support predictions made by the theory of atomic diffusion in the presence of a magnetic field. Simultaneously, these result support the possibility of the formation of unusual structures in stellar magnetic fields. Analysis of vertical stratification of the silicon and helium abundances shows that the boundaries of an abundance jump (in the two step model) are similar for each element; $\tau_{5000}$ = 0.8-1.2 for helium and 0.5-1.3 for silicon. The elemental abundances in the layers of effective formation of selected absorption lines for various phases are also correlated with the excitation energies of low transition levels: abundances are enhanced for higher excitation energy and higher optical depth within the applied model atmosphere.
We present simulations of dry-merger encounters between pairs of elliptical galaxies with dark matter halos. The aim of these simulations is to study the intergalactic stellar populations produced in both parabolic and hyperbolic encounters. We model progenitor galaxies with total-to-luminous mass ratios M_T/M_L 3 and 11. The initial mass of the colliding galaxies are chosen so that M_1/M_2 and 10. The model galaxies are populated by particles representing stars, as in Stanghellini et al. (2006), and dark matter. Merger remnants resulting from these encounters display a population of unbounded particles, both dark and luminous. The number of particles becoming unbounded depends on orbital configuration, with hyperbolic encounters producing a larger luminous intracluster population than parabolic encounters. Furthermore, in simulations with identical orbital parameters, a lower M_T/M_L of the colliding galaxies produces a larger fraction of unbounded luminous particles. For each modeled collision, the fraction of unbounded to initial stellar mass is the same in all mass-bins considered, similarly to what we found previously by modeling encounters of galaxies without dark halos. The fraction of intergalactic to total luminosity resulting from our simulations is ~ 4% and ~ 6% for dark-to-bright mass rations of 10 and 2 respectively. These unbounded-to-total luminous fractions are down from 17 % that we had previously found in the case of no dark halos. Our results are in broad agreement with intergalactic light observed in groups of galaxies, while the results of our previous models without dark halos better encompass observed intracluster populations. We suggest a possible formation scenario of intergalactic stars.
To investigate the nature and properties of far-infrared (FIR) sources from the AKARI Deep Field South (ADF-S), we performed an extensive search for the counterparts of 1000 ADF-S objects brighter than 0.0301 Jy in the WIDE-S (90 $\mu$m) AKARI band in the public databases (NED and SIMBAD). We analyzed the properties of the resulting sample: statistic of the identified objects, number counts, redshift distribution and morphological types. We also made a crude analysis of the clustering properties of the sources and constructed spectral energy distributions (SEDs) of 47 selected objects with the best photometry. Among 1000 investigated ADF-S sources, 545 were identified at other wavelengths. From them, 518 are known galaxies, and 343 of them were not known previously as infra-red sources. We found redshifts of 48 extragalactic objects and morphological types of 77 galaxies. We conclude that the bright FIR point sources observed in the ADF-S are mostly nearby galaxies.Their properties are very similar to properties of the local population of optically bright galaxies, except an unusually high ratio of peculiar or interacting objects and a smaller percentage of elliptical galaxies. The percentage of lenticular galaxies is the same as in the optically bright population which suggests they may frequently contain a significant amount of cool dust. It is possible that source confusion plays a significant role in more than 34% of measurements. The SEDs display a variety of galaxy types, from very actively star forming to very quiescent. Thanks to the AKARI long wavelength bands it was revealed for the first time that these galaxies form a population of objects with very cool dust.
Deviations from axial symmetry are necessary to maintain self-sustained MRI-turbulence. We define the parameters region where nonaxisymmetric MRI is excited and study dependence of the unstable modes structure and growth rates on the relevant parameters. We solve numerically the linear eigenvalue problem for global axisymmetric and nonaxisymmetric modes of standard-MRI in Keplerian disks with finite diffusion. For small magnetic Prandtl number the microscopic viscosity completely drops out from the analysis so that the stability maps and the growth rates expressed in terms of the magnetic Reynolds number Rm and the Lundquist number S do not depend on the magnetic Prandtl number Pm. The minimum magnetic field for onset of nonaxisymmetric MRI grows with Rm. For given S all nonaxisymmetric modes disappear for sufficiently high Rm. This behavior is a consequence of the radial fine-structure of the nonaxisymmetric modes resulting from the winding effect of differential rotation. It is this fine-structure which presents severe resolution problems for the numerical simulation of MRI at large Rm. For weak supercritical magnetic fields only axisymmetric modes are unstable. Nonaxisymmetric modes need stronger fields and not too fast rotation. If Pm is small its real value does not play any role in MRI.
Positive results of dark matter searches in experiments DAMA/NaI and DAMA/LIBRA taken together with negative results of other groups can imply nontrivial particle physics solutions for cosmological dark matter. Stable particles with charge -2 bind with primordial helium in O-helium "atoms" (OHe), representing a specific Warmer than Cold nuclear-interacting form of dark matter. Slowed down in the terrestrial matter, OHe is elusive for direct methods of underground Dark matter detection like those used in CDMS experiment, but its low energy binding with nuclei can lead to annual variations of energy release in the interval of energy 2-6 keV in DAMA/NaI and DAMA/LIBRA experiments. Schrodinger equation for system of nucleus and OHe is solved for a spherically symmetrical potential, formed by the Yukawa tail of nuclear scalar isoscalar attraction potential, acting on He beyond the nucleus, and dipole Coulomb repulsion between the nucleus and OHe at distances from the nuclear surface, smaller than the size of OHe. The values of coupling strength and mass of meson, mediating scalar isoscalar, are rather uncertain. Within the uncertainties of parameters of nuclear potential we find a range of these parameters, at which the sodium and/or iodine nuclei have a few keV binding energy with OHe. At nuclear parameters, reproducing DAMA results, the energy release predicted for detectors with chemical content other than NaI differ in the most cases from the one in DAMA detector. In particular, it is shown that in the case of CDMS germanium state has binding energy with OHe beyond the range of 2-6 keV and its formation should not lead to ionization in the energy range of DAMA signal. (abridged)
Massive protostars have associated bipolar outflows with velocities of hundreds of km s$^{-1}$. Such outflows can produce strong shocks when interact with the ambient medium leading to regions of non-thermal radio emission. We aim at exploring under which conditions relativistic particles are accelerated at the terminal shocks of the protostellar jets and can produce significant gamma-ray emission. We estimate the conditions necessary for particle acceleration up to very high energies and gamma-ray production in the non-thermal hot spots of jets associated with massive protostars embedded in dense molecular clouds. We show that relativistic Bremsstrahlung and proton-proton collisions can make molecular clouds with massive young stellar objects detectable by the {\it Fermi}{} satellite at MeV-GeV energies and by Cherenkov telescope arrays in the GeV-TeV range. Gamma-ray astronomy can be used to probe the physical conditions in star forming regions and particle acceleration processes in the complex environment of massive molecular clouds.
Characterizing the surfaces of rocky exoplanets via the scattered light will be an essential challenge to investigate the existence of life on habitable exoplanets. We present a simple reconstruction method for fractional areas of different surface types from photometric variations, or colors, of a second Earth. We create mock light curves for Earth without clouds using empirical data. Then these light curves are fitted to the isotropic scattering model consisting of 4 surface types: ocean, soil, snow and vegetation. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. We may be even able to detect a signature of vegetation from the distinct feature of photosynthesis on the Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere has an important effect, and for terrestrial exoplanets with atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously.
Nuclear disks and rings are frequent galaxy substructures, for a wide range of morphological types (from S0 to Sc). We have investigated the possible minor-merger origin of inner disks and rings in spiral galaxies through collisionless N-body simulations. The models confirm that minor mergers can drive the formation of thin, kinematically-cold structures in the center of galaxies out of satellite material, without requiring the previous formation of a bar. Satellite core particles tend to be deposited in circular orbits in the central potential, due to the strong circularization experienced by the satellite orbit through dynamical friction. The material of the satellite core reaches the remnant center if satellites are dense or massive, building up a thin inner disk; whereas it is fully disrupted before reaching the center in the case of low-mass satellites, creating an inner ring instead.
Comet 17P/Holmes was observed for linear polarisation using the optical polarimeter mounted on the 1.2m telescope atop Gurushikhar peak near Mt. Abu during the period November-December 2007. Observations were conducted through the IHW narrow band (continuum) filters. During the observing run the phase angle was near $13^{\circ}$ at which the comet showed negative polarisation. On the basis of the observed polarisation data we find comet 17P/Holmes to be a typical comet with usual dust characteristics. We note that radial rate of change of brightness in coma in red band is higher than that in blue band; it has decreased by a factor of 3.6 and 2.5 respectively in red and blue bands during the November - December run, indicating relative increase in the abundance of smaller dust particles out ward. Radial brightness variation seen near the nucleus on November 6 is indicative of the presence of a blob or shocked region beyond 10" from the nucleus which has gradually smoothened by December 13. The brightness distribution is found steeper during November 5-7 as compared to on December 13.
We investigate the dust size and dust shell structure of the bipolar
proto-planetary nebula M 1--92 by means of radiative transfer modeling. Our
models consists of a disk and bipolar lobes that are surrounded by an AGB
shell, each component having different dust characteristics. The upper limit of
the grain size $a_\mathrm{max}$ in the lobes is estimated to be $0.5 \mu$m from
the polarization value in the bipolar lobe. The $a_\mathrm{max}$ value of the
disk is constrained with the disk mass (0.2 $M_{\sun}$), which was estimated
from a previous CO emission line observation. We find a good model with
$a_\mathrm{max}=1000.0 \mu$m, which provides an approximated disk mass of 0.15
$M_{\sun}$. Even taking into account uncertainties such as the gas-to-dust mass
ratio, a significantly larger dust of $a_\mathrm{max}>100.0 \mu$m, comparing to
the dust in the lobe, is expected.
We also estimated the disk inner radius, the disk outer radius, and the
envelope mass to be 30 $R_\star$(=9 AU), 4500 AU, and 4 $M_{\sun}$,
respectively, where $v_\mathrm{exp}$ is the expansion velocity. If the dust
existing in the lobes in large separations from the central star undergoes
little dust processing, the dust sizes preserves the ones in the dust
formation. Submicron-sized grains are found in many objects besides M 1--92,
suggesting that the size does not depend much on the object properties, such as
initial mass of the central star and chemical composition of the stellar
system. On the other hand, the grain sizes in the disk do. Evidence of large
grains has been reported in many bipolar PPNs, including M 1--92. This result
suggests that disks play an important role in grain growth.
Recent advances in observational performance and numerical simulations have revolutionised our understanding of the solar chromosphere. This concerns in particular the structure and dynamics on small spatial and temporal scales. As a result, the picture of the solar chromosphere changed from an idealised static and plane-parallel stratification to a complex compound of intermittent domains, which are dynamically coupled to the layers below and above. In this picture, the chromosphere in a stricter sense is associated with the typical fibrillar structure shaped by magnetic fields like it is known from images taken in the H alpha line core. In internetwork regions below this layer, there exists a domain with propagating shock waves and weak magnetic fields, which both probably interact with the overlying large scale field. The existence of such a sub-canopy domain certainly depends on the properties of the overlying field. Details of the structure of the lower atmosphere can therefore be expected to vary significantly from location to location. Here, high-resolution observations, which were obtained with the CRISP filter at the Swedish Solar Telescope, are used to derive qualitative constraints for the atmospheric structure of quiet Sun regions.
Recently, high resolution observations with the help of the near-infrared adaptive optics integral field spectrograph SINFONI at the VLT proved the existence of massive and young nuclear star clusters in the centres of a sample of Seyfert galaxies. With the help of high resolution hydrodynamical simulations with the PLUTO-code, we follow the evolution of such clusters, especially focusing on mass and energy feedback from young stars. This leads to a filamentary inflow of gas on large scales (tens of parsec), whereas a turbulent and very dense disc builds up on the parsec scale. Here, we concentrate on the long-term evolution of the nuclear disc in NGC 1068 with the help of an effective viscous disc model, using the mass input from the large scale simulations and accounting for star formation in the disc. This two-stage modelling enables us to connect the tens of parsec scale region (observable with SINFONI) with the parsec scale environment (MIDI observations). At the current age of the nuclear star cluster, our simulations predict disc sizes of the order of 0.8 to 0.9 pc, gas masses of 1.0e6 Msun and mass transfer rates through the inner boundary of 0.025 Msun/yr in good agreement with values derived from observations.
Gamma-Ray Bursts (GRBs) have been regarded as standard candles at very high redshift for cosmology research. We have proposed a new method to calibrate GRB distance indicators with SNe Ia data in a completely cosmology independent way to avoid the circularity problem which limits the direct use of GRBs to probe cosmology. In this paper, a simple method is provided to combine GRB data into the joint observational data analysis to constrain cosmological models; in this method those SNe Ia data points used for calibrating the GRB data are not used to avoid any correlation between them. We find that the $\Lambda$CDM model is consistent with the joint data in 1-$\sigma$ confidence region, using the GRB data at high redshift calibrated with the interpolating method, the Constitution set of Type Ia supernova (SNe Ia), the Cosmic Microwave Background radiation (CMB) from Wilkinson Microwave Anisotropy Probe five year observation (WMAP5), the baryonic acoustic oscillation (BAO) from the spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy sample, the x-ray baryon mass fraction in clusters of galaxies, and the observational Hubble parameter versus redshift data. Comparing to the joint constraints with GRBs and without GRBs, we find that the contribution of GRBs to the joint cosmological constraints is a slight shift in the confidence regions of cosmological parameters to better enclose the $\Lambda$CDM model. Finally, we reconstruct the acceleration history of the Universe up to $z>6$ with the the distance moduli of SNe Ia and GRBs and find some features which deviate from the $\Lambda$CDM model and seem to favor oscillatory cosmology models; however further investigations are needed to better understand the situation.
Aims: We derive the probability density functions (PDFs) of column density for a complete sample of prominent molecular cloud complexes closer than 200 pc. Methods: We derive near-infrared dust extinction maps for 23 molecular cloud complexes, using the "nicest" colour excess mapping technique and data from the 2MASS archive. The extinction maps are then used to examine the column density PDFs in the clouds. Results: The column density PDFs of most molecular clouds are well-fitted by log-normal functions at low column densities (0.5 mag < A_v < 3-5 mag). However, at higher column densities prominent, power-law-like wings are common. In particular, we identify a trend among the PDFs: active star-forming clouds always have prominent non-log-normal wings. In contrast, clouds without active star formation resemble log-normals over the whole observed column density range, or show only low excess of higher column densities. This trend is also reflected in the cumulative PDFs, showing that the fraction of high column density material is significantly larger in star-forming clouds. These observations are in agreement with an evolutionary trend where turbulent motions are the main cloud-shaping mechanism for quiescent clouds, but the density enhancements induced by them quickly become dominated by gravity (and other mechanisms) which is strongly reflected by the shape of the column density PDFs. The dominant role of the turbulence is restricted to the very early stages of molecular cloud evolution, comparable to the onset of active star formation in the clouds.
Isolated galaxies have not been a hot topic over the past four decades. This is partly due to uncertainties about their existence. Are there galaxies isolated enough to be interesting? Do they exist in sufficient numbers to be statistically useful? Most attempts to compile isolated galaxy lists were marginally successful--too small number and not very isolated galaxies. If really isolated galaxies do exist then their value becomes obvious in a Universe where effects of interactions and environment (i.e. nurture) are important. They provide a means for better quantifying effects of nurture. The Catalog of Isolated Galaxies (CIG) compiled by Valentina Karachentseva appeared near the beginning of the review period. It becomes the focus of this review because of its obvious strengths and because the AMIGA project has increased its utility through a refinement (a vetted CIG). It contains almost 1000 galaxies with nearest neighbor crossing times of 1-3Gyr. It is large enough to serve as a zero-point or control sample. The galaxies in the CIG (and the distribution of galaxy types) may be significantly different than those in even slightly richer environments. The AMIGA-CIG, and future iterations, may be able to tell us something about galaxy formation. It may also allow us to better define intrinsic (natural) correlations like e.g. Fisher-Tully and FIR-OPTICAL. Correlations can be better defined when the dispersion added by external stimuli (nurture) is minimized or removed.
Fifty archival radio observations of the supergiant binary Cyg OB2 #5 using the Very Large Array over 20 years are re-examined to determine the location and character of the previously detected variable radio emission. The radio emission from the system consists of a primary component that is associated with the binary, and a non-thermal source (NE) that has been ascribed to a wind-collision region (WCR) between the stellar winds of the binary and that of a B-type star (Star D) to the NE. NE shows no evidence of variation in 23 epochs where it is resolved separately from the primary radio component, demonstrating that the variable emission arises in the primary. Since NE is non-variable, the radio flux from the primary can now be well determined for the first time, most especially in observations that do not resolve both the primary and NE components. The variable radio emission from the primary has a period of 6.7+/-0.3 years which is described by a simple model of a non-thermal source orbiting within the stellar wind envelope of the binary. Such a model implies the presence of a third, unresolved stellar companion (Star C) orbiting the 6.6-day binary with a period of 6.7 years. The variable non-thermal emission arises from either a WCR between Star C and the binary system, or possibly from Star C directly. The model gives a mass-loss rate of 3.4 x 10^{-5} solar mass/yr for Cyg OB2 #5, unusually high for an Of supergiant and comparable to that of WR stars, and consistent with an unusually strong He I 1.083-micron emission line, also redolent of WR stars. An examination of radial velocity observations suggests reflex motion of the binary due to Star C. The natures of NE and Star D are also examined. (abridged)
In this work we present a cosmic ray model that couples primary solar cosmic rays at the top of the Earth's atmosphere with the secondary ones detected at ground level by neutron monitors during Ground Level Enhancements (GLEs). The Neutron Monitor Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) Model constitutes a new version of the already existing NMBANGLE Model, differing in the solar cosmic ray spectrum assumed. The total output of the model is a multi-dimensional GLE picture that reveals part of the characteristics of the big solar proton events recorded at ground level. We apply both versions of the model to the GLE of 15 April 2001 (GLE60) and compare the results.
The main goal of the Andyrchy-BUST experiment is to study the primary cosmic rays spectrum and composition around the knee. The experimental data on the knee, as observed in the electromagnetic and high energy muon components, are presented. The electromagnetic component in our experiment is measured using the "Andyrchy" EAS array. High energy muon component (with 230 GeV threshold energy of muons) is measured using the Baksan Underground Scintillation Telescope (BUST). The location of the "Andyrchy" right above the BUST gives us a possibility for simultaneous measurements of both EAS components.
The Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) provides us with a unique possibility of studying a dwarf galaxy merging event while still in progress. Due to its low distance (25 kpc), the main body of Sgr dSph covers a vast area in the sky (roughly 15 x 7 degrees). Available photometric and spectroscopic studies have concentrated either on the central part of the galaxy or on the stellar stream, but the overwhelming majority of the galaxy body has never been probed. The aim of the present study is twofold. On the one hand, to produce color magnitude diagrams across the extension of Sgr dSph to study its stellar populations, searching for age and/or composition gradients (or lack thereof). On the other hand, to derive spectroscopic low-resolution radial velocities for a subsample of stars to determine membership to Sgr dSph for the purpose of high resolution spectroscopic follow-up. We used VIMOS-VLT to produce V and I photometry and spectroscopy on 7 fields across the Sgr dSph minor and major axis, plus 3 more centered on the associated globular clusters Terzan 7, Terzan 8 and Arp 2. A last field has been centered on M 54, lying in the center of Sgr dSph. We present photometry for 320,000 stars across the main body of Sgr dSph, one of the richest, and safely the most wide-angle sampling ever produced for this fundamental object. We also provide robust memberships for more than one hundred stars, whose high resolution spectroscopic analysis will be the object of forthcoming papers. Sgr dSph appears remarkably uniform among the observed fields. We confirm the presence of a main Sgr dSph population characterized roughly by the same metallicity of 47 Tuc, but we also found the presence of multiple populations on the peripheral fields of the galaxy, with a metallicity spanning from [Fe/H]=-2.3 to a nearly solar value.
We introduce AstroSim, a Second Life based prototype application for synchronous collaborative visualization targeted at astronomers.
Positive results of dark matter searches in DAMA/NaI and DAMA/LIBRA experiments, being put together with negative results of other groups, can imply nontrivial particle physics solutions for cosmological dark matter. Stable particles with charge -2 bind with primordial helium in O-helium "atoms" (OHe), representing a specific Warmer than Cold nuclear-interacting form of dark matter. Slowed down in the terrestrial matter, OHe is elusive for direct methods of underground Dark matter detection like those used in CDMS experiment, but its reactions with nuclei can lead to annual variations of energy release in the interval of energy 2-6 keV in DAMA/NaI and DAMA/LIBRA experiments. Schrodinger equation for system of nucleus and OHe is solved for spherically symmetrical potential well, formed by the Yukawa tail of nuclear scalar isoscalar attraction potential, acting on He beyond the nucleus, and dipole Coulomb repulsion between the nucleus and OHe at distances from the nuclear surface, smaller than the size of OHe. The window of parameters of this potential is found, at which the sodium and/or iodine nuclei have a few keV binding energy with OHe. At nuclear parameters, reproducing DAMA results, the energy release predicted for detectors with chemical content other than NaI differ in the most cases from the one in DAMA detector. In particular, it is shown that in the case of CDMS the energy of OHe-germanium bound state is beyond the range of 2-6 keV and its formation should not lead to ionization in the energy interval of DAMA signal. (abridged)
We investigate models of interacting dark matter and dark energy for the universe in a spatially flat Friedmann-Robertson-Walker (FRW) space-time. We find the "source equation" for the total energy density and determine the energy density of each dark component. We introduce an effective one-fluid description to evidence that interacting and unified models are related with each other, analyze the effective model and obtain the attractor solutions. We study linear and nonlinear interactions, the former comprises a linear combination of the dark matter and dark energy densities, their first derivatives, the total energy density, its first and second derivatives and a function of the scale factor. The latter is a possible generalization of the linear interaction consisting of an aggregate of the above linear combination and a significant nonlinear term built with a rational function of the dark matter and dark energy densities homogeneous of degree one. We solve the evolution equations of the dark components for both interactions and examine exhaustively several examples. There exist cases where the effective one-fluid description produces different alternatives to the $\La$CDM model and cases where the problem of coincidence is alleviated. In addition, we find that some nonlinear interactions yield an effective one-fluid model with a Chaplygin gas equation of state, whereas others generate cosmological models with de Sitter and power-law expansions. We show that a generic nonlinear interaction induces an effective equation of state which depends on the scale factor in the same way that the variable modified Chaplygin gas model, giving rise to the "relaxed Chaplygin gas model".
This paper presents, to the author's knowledge, the first graphics processing unit (GPU) accelerated program that solves the evolution of interacting scalar fields in an expanding universe. We present the implementation in NVIDIA's Compute Unified Device Architecture (CUDA) and compare the performance to other similar programs in chaotic inflation models. We report speedups between one and two orders of magnitude depending on the used hardware and software while achieving small errors in single precision. Simulations that used to last roughly one day to compute can now be done in hours and this difference is expected to increase in the future. The program has been written in the spirit of LATTICEEASY and users of the aforementioned program should find it relatively easy to start using CUDAEASY in lattice simulations. The program is available at this http URL under the GNU General Public License.
We analyze the dependence of the membership probabilities obtained from kinematical variables on the radius of the field of view around open clusters (the sampling radius, Rs). From simulated data, we show that the best discrimination between cluster members and non-members is obtained when the sampling radius is very close to the cluster radius. At higher Rs values more field stars tend to be erroneously assigned as cluster members. From real data of two open clusters (NGC 2323 and NGC 2311) we obtain that the number of identified cluster members always increases with increasing Rs. However, there is a threshold Rs value above which the identified cluster members are severely contaminated by field stars and the effectiveness of membership determination is relatively small. This optimal sampling radius is \sim 14 arcmin for NGC 2323 and \sim 13 arcmin for NGC 2311. We discuss the reasons for such behavior and the relationship between cluster radius and optimal sampling radius. We suggest that, independently of the method used to estimate membership probabilities, several tests using different sampling radius should be performed in order to evaluate the existence of possible biases.
The Transit Timing Variation (TTV) method relies on monitoring changes in timing of transits of known exoplanets. Non-transiting planets in the system can be inferred from TTVs by their gravitational interaction with the transiting planet. The TTV method is sensitive to low-mass planets that cannot be detected by other means. Here we describe a fast algorithm that can be used to determine the mass and orbit of the non-transiting planets from the TTV data. We apply our code, ttvim.f, to a wide variety of planetary systems to test the uniqueness of the TTV inversion problem and its dependence on the precision of TTV observations. We find that planetary parameters, including the mass and mutual orbital inclination of planets, can be determined from the TTV datasets that should become available in near future. Unlike the radial velocity technique, the TTV method can therefore be used to characterize the inclination distribution of multi-planet systems.
The Gas Pixel Detector, recently developed and continuously improved by Pisa INFN in collaboration with IASF-Roma of INAF, can visualize the tracks produced within a low Z gas by photoelectrons of few keV. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the linear polarization of X-rays, while preserving the information on the absorption point, the energy and the time of individual photons. Applied to X-ray Astrophysics, in the focus of grazing incidence telescopes, it can perform angular resolved polarimetry with a huge improvement of sensitivity, when compared with the conventional techniques of Bragg diffraction at 45 degrees and Compton scattering around 90 degrees. This configuration is the basis of POLARIX and HXMT, two pathfinder missions, and is included in the baseline design of IXO, the very large X-ray telescope under study by NASA, ESA and JAXA.
In the Sloan Digital Sky Survey (SDSS) quasars are targeted using colors and anything that can cause the identifying characteristics of the colors to disappear can create problems in the source selection process. Quasar spectra contain strong emission lines that can seriously affect the colors in photometric systems in which the transmission characteristics vary abruptly and significantly with redshift. When a strong line crosses a gap between two filter passbands the color effects induced by the line change abruptly, and there is also a dimming in apparent brightness compared to those redshifts where the strong line is inside a filter passband where the transmission is high. The strong emission lines in quasars, combined with the varying detectability introduced by the transmission pattern of the five filters, will result in a filter-gap footprint being imprinted on the N(z) distribution, with more quasars being missed when a strong line falls in a filter gap. It is shown here that a periodicity of Delta(z)~0.6 is imprinted on the redshift-number distribution by this selection effect. Because this effect cannot be rigorously corrected for, astronomers need to be aware of it in any investigation that uses the SDSS N(z) distribution. Its presence also means that the SDSS quasar data cannot be used either to confirm or to rule out the Delta(z)~0.6 redshift period reported previously in other, unrelated quasar data.
Although recent work in numerical relativity has made tremendous strides in quantifying the gravitational wave luminosity of black hole mergers, very little is known about the electromagnetic luminosity that might occur in immediate conjunction with these events. We show that whenever the heat deposited in the gas near a pair of merging black holes is proportional to its total mass, and the surface density of the gas in the immediate vicinity is greater than the (quite small) amount necessary to make it optically thick, the characteristic scale of the luminosity emitted in direct association with the merger is the Eddington luminosity independent of the gas mass. The duration of the photon signal is proportional to the gas mass, and is generally rather longer than the merger event. At somewhat larger distances, dissipation associated with realigning the gas orbits to the new spin orientation of the black hole can supplement dissipation of the energy gained from orbital adjustment to the mass lost in gravitational radiation; these two heat sources can combine to augment the electromagnetic radiation over longer timescales.
Previously unobservable mirror asymmetry of the solar magnetic field -- a key ingredient of the dynamo mechanism which is believed to drive the 11-year activity cycle -- has now been measured. This was achieved through systematic monitoring of solar active regions carried out for more than 20 years at observatories in Mees, Huairou, and Mitaka. In this paper we report on detailed analysis of vector magnetic field data, obtained at Huairou Solar Observing Station in China. Electric current helicity (the product of current and magnetic field component in the same direction) was estimated from the data and a latitude-time plot of solar helicity during the last two solar cycles has been produced. We find that like sunspots helicity patterns propagate equatorwards but unlike sunspot polarity helicity in each solar hemisphere does not change sign from cycle to cycle - confirming the theory. There are, however, two significant time-latitudinal domains in each cycle when the sign does briefly invert. Our findings shed new light on stellar and planetary dynamos and has yet to be included in the theory.
Over the past 15 years, our knowledge of the interior of the Sun has tremendously progressed by the use of helioseismic measurements. However, to go further in our understanding of the solar core, we need to measure gravity (g) modes. Thanks to the high quality of the Doppler-velocity signal measured by GOLF/SoHO, it has been possible to unveil the signature of the asymptotic properties of the solar g modes, thus obtaining a hint of the rotation rate in the core. However, the quest for the detection of individual g modes is not yet over. In this work, we apply the latest theoretical developments to guide our research using GOLF velocity time series. In contrary to what was thought till now, we are maybe starting to identify individual low-frequency g modes...
The results of speckle interferometric measurements of binary and multiple stars conducted in 2008 and 2009 at the Blanco and SOAR 4-m telescopes in Chile are presented. A total of 1898 measurements of 1189 resolved pairs or sub-systems and 394 observations of 285 un-resolved targets are listed. We resolved for the first time 48 new pairs, 21 of which are new sub-systems in close visual multiple stars. Typical internal measurement precision is 0.3 mas in both coordinates, typical companion detection capability is $\Delta m \sim 4.2$ at 0\farcs15 separation. These data were obtained with a new electron-multiplication CCD camera; data processing is described in detail, including estimation of magnitude difference, observational errors, detection limits, and analysis of artifacts. We comment on some newly discovered pairs and objects of special interest.
A new accelerating cosmology driven only by baryons plus cold dark matter (CDM) is proposed in the framework of general relativity. In this model the present accelerating stage of the Universe is powered by the negative pressure describing the gravitationally-induced particle production of cold dark matter particles. This kind of scenario has only one free parameter and the differential equation governing the evolution of the scale factor is exactly the same of the $\Lambda$CDM model. For a spatially flat Universe, as predicted by inflation ($\Omega_{dm}+\Omega_{baryon}=1$), it is found that the effectively observed matter density parameter is $\Omega_{meff} = 1- \alpha$, where $\alpha$ is the constant parameter specifying the CDM particle creation rate. The supernovae test based on the Union data (2008) requires $\alpha\sim 0.71$ so that $\Omega_{meff} \sim 0.29$ as independently derived from weak gravitational lensing, the large scale structure and other complementary observations.
The fact that one can associate thermodynamic properties with horizons brings together principles of quantum theory, gravitation and thermodynamics and possibly offers a window to the nature of quantum geometry. This review discusses certain aspects of this topic concentrating on new insights gained from some recent work. After a brief introduction of the overall perspective, Sections 2 and 3 provide the pedagogical background on the geometrical features of bifurcation horizons, path integral derivation of horizon temperature, black hole evaporation, structure of Lanczos-Lovelock models, the concept of Noether charge and its relation to horizon entropy. Section 4 discusses several conceptual issues introduced by the existence of temperature and entropy of the horizons. In Section 5 we take up the connection between horizon thermodynamics and gravitational dynamics and describe several peculiar features which have no simple interpretation in the conventional approach. The next two sections describe the recent progress achieved in an alternative perspective of gravity. In Section 6 we provide a thermodynamic interpretation of the field equations of gravity in any diffeomorphism invariant theory and in Section 7 we obtain the field equations of gravity from an entropy maximization principle. The last section provides a summary.
Dark matter decaying or annihilating into mu+mu- or tau+tau- has been proposed as an explanation for the e+e- anomalies reported by PAMELA and Fermi. Recent analyses show that IceCube, supplemented by DeepCore, will be able to significantly constrain the parameter space of decays to mu+mu-, and rule out decays to tau+tau- and annihilations to mu+mu- in less than five years of running. These analyses rely on measuring track-like events in IceCube+DeepCore from down-going nu_mu. In this paper we show that by instead measuring cascade events, which are induced by all neutrino flavors, IceCube+DeepCore can rule out decays to mu+mu- in only three years of running, and rule out decays to tau+tau- and annihilation to mu+mu- in only one year of running. These constraints are highly robust to the choice of dark matter halo profile and independent of dark matter-nucleon cross-section.
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We investigate the physical properties of the 10 blazars at redshift greater than 2 detected in the 3-years all sky survey performed by the Burst Alert Telescope (BAT) onboard the Swift satellite. We find that the jets of these blazars are among the most powerful known. Furthermore, the mass of their central black hole, inferred from the optical-UV bump, exceeds a few billions of solar masses, with accretion luminosities being a large fraction of the Eddington one. We compare their properties with those of the brightest blazars of the 3-months survey performed by the Large Area Telescope (LAT) onboard the Fermi satellite. We find that the BAT blazars have more powerful jets, more luminous accretion disks and larger black hole masses than LAT blazars. These findings can be simply understood on the basis of the blazar sequence, that suggests that the most powerful blazars have a spectral energy distribution with a high energy peak at MeV (or even sub-MeV)energies. This implies that the most extreme blazars can be found more efficiently in hard X-rays, rather than in the high energy gamma-ray band. We then discuss the implications of our findings for future missions, such as the New Hard X-ray Mission (NHXM) and especially the Energetic X-ray Imaging Survey Telescope (EXIST) mission which, during its planned 2 years all sky survey, is expected to detect thousands of blazars, with a few of them at z greater than 6.
We present radial velocities of the very low-mass star VB10 obtained over a time span of 0.61 yr as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the VLT with an ammonia gas cell. The typical internal precision of the measurements is 10 m/s. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo and Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ~1 km/s radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M > 3 M_Jup and the orbital period and inclination suggested by Pravdo and Shaklan at better than 5 sigma confidence. Planets with masses down to 1 M_Jup would need to have unusually large orbital eccentricities (e > 0.7) and be phased in a very specific way to have eluded detection with our data. We conclude that the planet detection claimed by Pravdo and Shaklan is spurious on the basis of these results. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low-mass stars.
(Abridged) OJ287 is a BL Lac object that has shown double-peaked bursts at regular intervals of ~12 yr during the last ~40 yr. We analyse optical photopolarimetric monitoring data from 2005-2009, during which the latest double-peaked outburst occurred. The aim of this study is twofold: firstly, we aim to analyse variability patterns and statistical properties of the optical polarization light-curve. We find a strong preferred position angle in optical polarization. The preferred position angle can be explained by separating the jet emission into two components: an optical polarization core and chaotic jet emission. The optical polarization core is stable on time scales of years and can be explained as emission from an underlying quiescent jet component. The chaotic jet emission sometimes exhibits a circular movement in the Stokes plane. We interpret these events as a shock front moving forwards and backwards in the jet, swiping through a helical magnetic field. Secondly, we use our data to assess different binary black hole models proposed to explain the regularly appearing double-peaked bursts in OJ287. We compose a list of requirements a model has to fulfil. The list includes not only characteristics of the light-curve but also other properties of OJ287, such as the black hole mass and restrictions on accretion flow properties. We rate all existing models using this list and conclude that none of the models is able to explain all observations. We discuss possible new explanations and propose a new approach to understanding OJ287. We suggest that both the double-peaked bursts and the evolution of the optical polarization position angle could be explained as a sign of resonant accretion of magnetic field lines, a 'magnetic breathing' of the disc.
We present a new method to identify large scale filaments and apply it to a cosmological simulation. Using positions of haloes above a given mass as node tracers, we look for filaments between them using the positions and masses of all the remaining dark-matter haloes. In order to detect a filament, the first step consists in the construction of a backbone linking two nodes, which is given by a skeleton-like path connecting the highest local dark matter (DM) density traced by non-node haloes. We estimate the characteristic DM density between two skeleton-candidate haloes using two approximations, i) the Voronoi tessellation density when the distance between haloes is similar or smaller than the sum of their virial radii, and ii) when the distance is larger, using a proxy of the minimum DM density between the two haloes assuming NFW profiles. The filament quality is defined by a density and gap parameters characterising its skeleton, and filament members are selected by their binding energy in the plane perpendicular to the filament. This membership condition is associated to characteristic orbital times; however if one assumes a fixed orbital timescale for all the filaments, the resulting distributions of filament thickness and integrated mass are consistent with the results using the full binding energy condition. Therefore, this simplified set of conditions allows the method to be applied to observational data with no dynamical information, while ensuring a reduced amount of systematic biases. We test the method in the simulation using massive haloes(M>10^14Msun/h) as filament nodes, and study several statistical properties of the resulting filaments. (Abridged)
We argue that the recent groundbreaking discovery by Badenes et al. (2009) of a nearby (~50 pc) white dwarf-neutron star (or black hole) binary (SDSS 1257+5428) with a merger timescale ~500 Myr implies that such systems are common; we estimate that there are of order 10^6 in the Galaxy. Although subject to large uncertainties, the nominal derived merger rate is ~5 x 10^-4 per yr in the Milky Way, just ~3-6 and ~20-40 times less than the Type Ia and core-collapse supernova (SN) rates, respectively. This implies that the merger rate is ~0.5-1 x 10^4 per Gpc^3 per yr in the local universe, ~5000-10000 times more than the observed (beaming-uncorrected) long-duration gamma-ray burst (GRB) rate. We estimate the lower limit on the rate in the Galaxy to be >2.5 x 10^-5 per yr at 95% confidence. We briefly discuss the implications of this finding for the census of long- and short-duration GRBs and their progenitors, the frequency of tight binary companions to Type Ib/c SN progenitors, the origin of ultra-high energy cosmic rays (UHECRs), the formation of rapidly rotating neutron stars and ~2-3 M_sun black holes, the census of faint Ia-like SNe, as well as for upcoming and current transient surveys (e.g., LOSS, PTF, LSST), and for high- (LIGO) and low-frequency (LISA) gravitational wave searches.
In a sample of about 45,700 early-type galaxies extracted from SDSS, we find that the shape, normalization, and dispersion around the mean size-stellar mass relation is the same for young and old systems, provided the stellar mass is greater than 3*10^10 Msun. This is difficult to reproduce in pure passive evolution models, which generically predict older galaxies to be much more compact than younger ones of the same stellar mass. However, this aspect of our measurements is well reproduced by hierarchical models of galaxy formation. Whereas the models predict more compact galaxies at high redshifts, subsequent minor, dry mergers increase the sizes of the more massive objects, resulting in a flat size-age relation at the present time. At lower masses, the models predict that mergers are less frequent, so that the expected anti-correlation between age and size is not completely erased. This is in good agreement with our data: below 3*10^10 Msun, the effective radius R_e is a factor of ~2 lower for older galaxies. These successes of the models are offset by the fact that the predicted sizes have other serious problems, which we discuss.
We examine the impact of environment on the dynamical structure of satellite systems based on the Millennium--II Simulation. Satellite halos are defined as sub--halos within the virial radius of a host halo. The satellite sample is restricted to those sub--halos which showed a maximum circular velocity above 30 km/s at the time of accretion. Host halo masses range from 10^10 to 10^14 Msol/h. We compute the satellites' average accretion redshift, z_acc, velocity dispersion, sigma, and velocity anisotropy parameter, beta, utilising stacked satellite samples of equal mass hosts at similar background densities. The main results are: (1) On average satellites within hosts in high density environments are accreted earlier (Delta z ~ 0.1) compared to their counterparts at low densities. For host masses above 5 times 10^13 Msol/h this trend weakens and may reverse for higher host masses; (2) The velocity dispersion of satellites in low density environments follows that of the host, i.e. no velocity bias is observed for host halos at low densities independent of host mass. However, for low mass hosts in high density environments the velocity dispersion of the satellites can be a few times larger than that of the host halo, i.e. the satellites are dynamically hotter than their host halos. (3) The anisotropy parameter depends on host mass and environment. Satellites of massive hosts show more radially biased velocity distributions. Moreover in low density environments satellites have more radially biased velocities (Delta beta > 0.1) compared to their counterparts in high density environments. We believe that our approach allows one to predict a similar behaviour for observed satellite galaxy systems.
Although the relationship between the far-infrared and cm-wave radio luminosities of normal galaxies is one of the most striking correlations in astronomy, a solid understanding of its physical basis is lacking. In one interpretation, the "calorimeter model," rapid synchrotron cooling of cosmic ray electrons is essential in reproducing the observed linear relationship. Observed radio spectra, however, are shallower than what is expected of cooled synchrotron emission. In Thompson et al. (2006), a simple parameterized model is presented to explain how relatively shallow observed spectra might arise even in the presence of rapid synchrotron cooling by accounting for ionization losses and other cooling mechanisms. During the commissioning of the 42-element Allen Telescope Array, we observed the starburst galaxies M82, NGC 253, and Arp 220 at frequencies ranging from 1 to 7 GHz, obtaining unprecedented broadband continuous radio spectra of these sources. We combine our observations with high-frequency data from the literature to separate the spectra into thermal and nonthermal components. The nonthermal components all steepen in the cm-wave regime and cannot be well-modeled as simple power laws. The model of Thompson et al. is consistent with our M82 results when plausible parameters are chosen, and our results in fact significantly shrink the space of allowed model parameters. The model is only marginally consistent with our NGC 253 data. Assuming the Thompson et al. model, a steep electron energy injection index of p = -2.5 is ruled out in M82 and NGC 253 to >99% confidence. We describe in detail the observing procedures, calibration methods, analysis, and consistency checks used for broadband spectral observations with the Allen Telescope Array.
We study the parameter space of cold dark matter axions in two cosmological scenarios with non-standard thermal histories before Big Bang nucleosynthesis: the Low Temperature Reheating (LTR) cosmology and the kination cosmology. If the Peccei-Quinn symmetry breaks during inflation, we find more allowed parameter space in the LTR cosmology than in the standard cosmology and less in the kination cosmology. On the contrary, if the Peccei-Quinn symmetry breaks after inflation, the Peccei-Quinn scale is orders of magnitude higher than standard in the LTR cosmology and lower in the kination cosmology. We show that the axion velocity dispersion may be used to distinguish some of these non-standard cosmologies. Thus, axion cold dark matter may be a good probe of the history of the Universe before Big Bang nucleosynthesis.
We study the impact of gas motions on the polarization of bright X-ray emission lines from the hot intercluster medium (ICM). The polarization naturally arises from resonant scattering of emission lines owing to a quadrupole component in the radiation field produced by a centrally peaked gas density distribution. If differential gas motions are present then a photon emitted in one region of the cluster will be scattered in another region only if their relative velocities are small enough and the Doppler shift of the photon energy does not exceed the line width. This affects both the degree and the direction of polarization. The changes in the polarization signal are in particular sensitive to the gas motions perpendicular to the line of sight. We calculate the expected degree of polarization for several patterns of gas motions, including a slow inflow expected in a simple cooling flow model and a fast outflow in an expanding spherical shock wave. In both cases, the effect of non-zero gas velocities is found to be minor. We also calculate the polarization signal for a set of clusters, taken from large-scale structure simulations and evaluate the impact of the gas bulk motions on the polarization signal. We argue that the expected degree of polarization is within reach of the next generation of space X-ray polarimeters.
The hadron-quark phase transition in the interior of compact stars is investigated, when the transition proceeds through a mixed phase. The hadronic phase is described in the framework of relativistic mean-field theory, when also the scalar-isovector delta-meson mean-field is taken into account. The changes of the parameters of phase transition caused by the presence of delta-meson field are explored. The results of calculation of structure of the mixed phase(Glendenning construction) are compared with the results of usual first-order phase transition (Maxwell construction).
We present the recently derived Wolf et al. (2009) mass estimator, which is applicable for spherical pressure-supported stellar systems spanning over ten orders of magnitude in luminosity, as a tool to test galaxy formation theories. We show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are consistent with having formed within a halo of mass approximately 3 x 10^9 Msun in LCDM cosmology. The faintest MW dSphs seem to have formed in dark matter halos that are at least as massive as those of the brightest MW dSphs, despite the almost five orders of magnitude spread in luminosity. We expand our analysis to the full range of observed pressure-supported stellar systems and examine their half-light I-band mass-to-light ratios. The M/L vs. half-light mass M_1/2 relation for pressure-supported galaxies follows a U-shape, with a broad minimum near M/L ~ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to M/L ~ 3,200 for ultra-faint dSphs, and a more shallow rise to M/L ~ 800 for galaxy cluster spheroids.
The Kerr spacetime of spinning black holes is one of the most intriguing predictions of Einstein's theory of general relativity. The special role this spacetime plays in the theory of gravity is encapsulated in the no-hair theorem, which states that the Kerr metric is the only realistic black-hole solution of the vacuum field equations. Recent and anticipated advances in the observations of black holes throughout the electromagnetic spectrum have secured our understanding of their basic properties while opening up new opportunities for devising tests of the Kerr metric. In this paper, we argue that imaging and spectroscopic observations of accreting black-holes with current and future instruments can lead to the first direct test of the no-hair theorem.
We present the results of X-ray spectral analysis of two mini-BAL QSOs, PG 1126-041 and PG 1351+640, aimed at getting insights into the physics of quasar outflows. We find strong X-ray spectral variability on timescales of years. These variations can be well reproduced by variations of physical properties as the covering factor and column density of ionized gas along the line of sight, compatible with radiatively-driven accretion disk wind models.
We present the results of a search for galaxy clusters in Subaru-XMM Deep
Field. We reach a depth for a total cluster flux in the 0.5-2 keV band of
2x10^{-15} ergs cm^{-2} s^{-1} over one of the widest XMM-Newton contiguous
raster surveys, covering an area of 1.3 square degrees. Cluster candidates are
identified through a wavelet detection of extended X-ray emission. The red
sequence technique allows us to identify 57 cluster candidates. We report on
the progress with the cluster spectroscopic follow-up and derive their
properties based on the X-ray luminosity and cluster scaling relations. In
addition, 3 sources are identified as X-ray counterparts of radio lobes, and in
3 further sources, X-ray counterpart of radio lobes provides a significant
fraction of the total flux of the source. In the area covered by NIR data, our
identification success rate achieves 86%. We detect a number of radio galaxies
within our groups and for a luminosity-limited sample of radio galaxies we
compute halo occupation statistics using a marked cluster mass function. We
compare the cluster detection statistics in the SXDF with the predictions of
concordance cosmology and current knowledge of the X-ray cluster properties,
concluding that a reduction of concordance sigma_8 value by 5% is required in
order to match the prediction of the model and the data. This conclusion still
needs verification through the completion of cluster follow-up.
It depends on the state of matter at supra-nuclear density to model pulsar's structure, which is unfortunately not certain due to the difficulties in physics. In cold quark matter at realistic baryon densities of compact stars (with an average value of $\sim 2-3\rho_0$), the interaction between quarks is so strong that they would condensate in position space to form quark-clusters. We argue that quarks in quark stars are grouped in clusters, then we apply two phenomenological models for quark stars, the polytropic model and Lennard-Jones model. Both of the two models have stiffer EoS, and larger maximum mass for quark stars (larger than 2 $M_\odot$). The gravitational energy releases during the AIQ process could explain the observed energy of three supergiant flares from soft gamma-ray repeaters ($\sim 10^{47}$ ergs).
We have discovered a remarkable warm (140 - 160 K) molecular hydrogen tail with a mass of approximately 2.5*10^7 M_sun extending 20 kpc from a cluster spiral galaxy, ESO 137-001, in Abell 3627. Some portion of this gas is lost permanently to the intracluster medium, as the tail extends beyond the tidal radius of the galaxy. We also detect a hot (580 - 680 K) component in the tail that is approximately 1% of the mass of the warm component. This discovery is direct evidence that the galaxy is currently undergoing ram-pressure stripping, as also indicated by its X-ray and H\alpha tail found by other studies. We estimate the galaxy is losing its interstellar gas at a rate of at least ~ 1 - 2 M_sun yr^-1. If the galaxy persists to lose mass at this estimated rate, it will exhaust its gas reservoir in a single pass through the cluster core, which will take approximately 0.5 - 1 Gyr. The results produced from the modeling of the ram-pressure stripping timescale are consistent with our upper limit and suggest that the effects of ram-pressure are most likely to be seen when the galaxy approaches the outskirts of the cluster core for the first time. We also study the star forming properties of the galaxy and its tail, and we identify most of the previously discovered external H\alpha sources within the tail in our 8 micron data but not in our 3.6 micron data, confirming these sources are HII regions. IRS spectroscopy of the region containing these H\alpha sources also reveals aromatic features associated with star formation. We conclude that star-formation is not occurring throughout the molecular hydrogen tail but only immediately downstream of the galaxy. Gas-stripping may be a turbulent process where stars form within high density eddies in the stripped gas.
Physical Research Laboratory's (PRL) Optical Polarimeter has been used on various telescopes in India since its development in-house in the mid 1980s. To make the instrument more efficient and effective we have designed the acquisition and control system and written the software to run on the GNU/Linux Operating System. CCD cameras have been used, in place of eyepieces, which allow to observe fainter sources with smaller apertures. The use of smaller apertures provides dramatic gains in the signal-to-noise ratio. The polarimeter is now fully automated resulting in increased efficiency. With the advantage of networking being built-in at the operating system level in GNU/Linux, this instrument can now be controlled from anywhere on the PRL local area network which means that the observer can be stationed in Ahmedabad / Thaltej as well or via ssh anywhere on the internet. The current report provides an overview of the system as implemented.
The ESA gamma-ray observatory INTEGRAL, launched on 17 October 2002, continues to produce a wealth of discoveries and new results on compact high energy Galactic objects, nuclear gamma-ray line emission, diffuse line and continuum emission, cosmic background radiation, AGN, high energy transients and sky surveys. The observing programme, fully open to the scientific community at large, is built from the community's feedback to the Announcements of Opportunity, issued about once per year. The mission's technical status is healthy and INTEGRAL is continuing its scientific operations well beyond its 5-year technical design lifetime. This paper will briefly summarize the overall current status.
We describe a focal plane array (FPA) system, called Apertif, that is being developed for the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is to increase the instantaneous field of view of the WSRT by a factor of 37 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications such as deep imaging surveys of the northern sky of HI and OH emission, of the polarised continuum and efficient searches for pulsars and transients. Such surveys will detect the HI in more than 100,000 galaxies out to z = 0.4, will allow to determine the detailed structure of the magnetic field of the Galaxy, and will discover more than 1,000 pulsars. We present experimental results obtained with a prototype FPA installed in one of the WSRT dishes. These results demonstrate that FPAs do have the performance that is required to make all these surveys possible.
Relatively small amounts (typically between 2-200 parts per million) of presolar grains have been preserved in the matrices of chondritic meteorites. The measured abundances of the different types of grains are highly variable from one chondrite to another, but are higher in unequilibrated chondrites that have experienced little or no aqueous alteration and/or metamorphic heating than in processed meteorites. A general overview of the abundances measured in presolar grains (particularly the recently identified presolar silicates) contained in primitive chondrites is presented. Here we will focus on the most primitive chondrite groups, as typically the highest measured abundances of presolar grains occur in primitive chondrites that have experienced little thermal metamorphism. Looking at the most aqueously altered chondrite groups, we find a clear pattern of decreasing abundance of presolar silicate grains with increasing level of aqueous alteration. We conclude that the measured abundances of presolar grains in altered chondrites are strongly biased by their peculiar histories. Scales quantifying the intensity of aqueous alteration and shock metamorphism in chondrites could correlate with the content in presolar silicates. To do this it would be required to infer the degree of destruction or homogenization of presolar grains in the matrices of primitive meteorites. To get an unbiased picture of the relative abundance of presolar grains in the different regions of the protoplanetary disk where first meteorites consolidated, future dedicated studies of primitive meteorites, IDPs, and collected materials from sample-return missions (like e.g. the planned Marco Polo) are urgently required.
A discussion of the time scales in the s process appears to be an approriate aspect to discuss at the occasion of 70th anniversary of Roberto Gallino, the more as this subject has been repeatedly addressed during the 20 years of collaboration between Torino and Karlsruhe. The two chronometers presented in this text were selected to illustrate the intense mutual stimulation of both groups. Based on a reliable set of accurate stellar (n, gamma) cross sections determined mostly at FZK, the Torino group succeeded to develop a comprehensive picture of the various s-process scenarios, which are most valuable for understanding the composition of the solar system as well as for the interpretation of an increasing number of astronomical observations.
After the first meeting in Copenhagen in 2001 QSQCD II is the second workshop in this series dealing with cosmic matter at very high density and its astrophysical implications. The aim is to bring together reseachers in the physics of compact stars, both theoretical and observational. Consequently a broad range of topics was presented, reviewing extremely energetic cosmological events and their relation to the high-density equation of state of strong-interaction matter. This summary elucidates recent progress in the field, as presented by the participants, and comments on pertinent questions for future developments.
Magnetic-field generation by a relativistic ion beam propagating through an electron-ion plasma along a homogeneous magnetic field is investigated with 2.5D high-resolution particle-in-cell (PIC) simulations. The studies test predictions of a strong amplification of short-wavelength modes of magnetic turbulence upstream of nonrelativistic and relativistic parallel shocks associated with supernova remnants, jets of active galactic nuclei, and gamma-ray bursts. We find good agreement in the properties of the turbulence observed in our simulations compared with the dispersion relation calculated for linear waves with arbitrary orientation of ${\vec k}$. Depending on the parameters, the backreaction on the ion beam leads to filamentation of the ambient plasma and the beam, which in turn influences the properties of the magnetic turbulence. For mildly- and ultra-relativistic beams, the instability saturates at field amplitudes a few times larger than the homogeneous magnetic field strength. This result matches our recent studies of nonrelativistically drifting, hot cosmic-ray particles upstream of supernova-remnant shocks which indicated only a moderate magnetic-field amplification by nonresonant instabilities. We also demonstrate that the aperiodic turbulence generated by the beam can provide efficient particle scattering with a rate compatible with Bohm diffusion. Representing the ion beam as a constant external current, i.e. excluding a backreaction of the magnetic turbulence on the beam, we observe non-resonant parallel modes with wavelength and growth rate as predicted by analytic calculations. In this unrealistic setup the magnetic field is amplified to amplitudes far exceeding the homogeneous field, as observed in recent MHD and PIC simulations.
By coupling a solar surface flux transport model with an extrapolation of the heliospheric field, we simulate the evolution of the Sun's open magnetic flux and the heliospheric current sheet (HCS) based on observational data of sunspot groups since 1976. The results are consistent with measurements of the interplanetary magnetic field near Earth and with the tilt angle of the HCS as derived from extrapolation of the observed solar surface field. This opens the possibility for an improved reconstruction of the Sun's open flux and the HCS into the past on the basis of empirical sunspot data.
We create a model for recovering the intrinsic, absorption-corrected surface
brightness distribution of a galaxy and apply the model to the M31.
We construct a galactic model as a superposition of axially symmetric stellar
components and a dust disc to analyse the intrinsic absorption efects. Dust
column density is assumed to be proportional to the far-infrared flux of the
galaxy. Along each line of sight, the observed far-infrared spectral energy
distribution is approximated with modified black body functions considering
dust components with different temperatures, allowing to determine the
temperatures and relative column densities of the dust components.
We apply the model to the nearby galaxy M31 using the Spitzer Space Telescope
far-infrared observations for mapping dust distribution and temperature. A warm
and a cold dust component are distinguished. The temperature of the warm dust
in M31 varies between 56 and 60 K and is highest in the spiral arms; the
temperature of the cold component is mostly 15-19 K and rises up to about 25 K
at the centre of the galaxy. The intensity-weighted mean temperature of the
dust decreases from T ~32 K at the centre to T ~20 K at R ~7 kpc and outwards.
We also calculate the intrinsic UBVRIL surface brightness distributions and the
spatial luminosity distribution. The intrinsic dust extinction in the V-colour
rises from 0.25 mag at the centre to 0.4-0.5 mag at R = 6-13 kpc and decreases
smoothly thereafter. The calculated total extinction-corrected luminosity of
M31 is L_B = (3.64 pm 0.15) 10^10L_sun, corresponding to an absolute luminosity
M_B = (-20.89 pm 0.04) mag. Of the total B-luminosity, 20% (0.24 mag) is
obscured from us by the dust inside M31. The intrinsic shape of the bulge is
slightly prolate in our best-fit model.
A new accreting millisecond X-ray pulsar, IGR J17511-3057, was discovered in outburst on 2009 September 12 during the INTEGRAL Galactic bulge monitoring programme. To study the evolution of the source X-ray flux and spectral properties during the outburst, we requested a Swift monitoring of IGRJ17511-3057. In this paper we report on the results of the first two weeks of monitoring the source. The persistent emission of IGR J17511-3057 during the outburst is modeled well with an absorbed blackbody (kT~0.9 keV) and a power-law component (photon index~1-2), similar to what has been observed from other previously known millisecond pulsars. Swift also detected three type-I Xray bursts from this source. By assuming that the peak luminosity of these bursts is equal to the Eddington value for a pure helium type-I X-ray burst, we derived an upper limit to the source distance of ~10 kpc. The theoretical, expected recurrence time of the bursts according to the helium burst hypothesis is 0.2-0.9 days, in agreement with the observations.
(Abridged) We report on a consistent and comprehensive spectral analysis of the X-ray emission of 25 Black Hole X-ray Binaries. All publicly available observations of the black hole binaries in the RXTE archive were analysed. Three different types of model were fitted to investigate the spectral changes occurring during an outburst. For the population, as well as each binary and each outburst from each binary, we construct two diagnostic diagrams. The Hardness Intensity/Luminosity Diagram (HID/HLD) is most useful when studying a single binary. However, to compare between different binary systems, the Disc Fraction Luminosity diagram (DFLD) is more useful. We discuss the limitations of both diagnostic diagrams for the study of the X-ray binary outbursts, and we clearly illustrate how the two diagrams map onto each other for real outburst data. We extract the peak luminosities in a single outburst, as well as the luminosities at the transitions away from- and returning to the powerlaw dominated state for each outburst. The distribution of the luminosities at the transition from the powerlaw to the disc dominated state peaks at around 0.3L_Edd, the same as the peak of the distribution of the peak luminosities in an outburst. Using the disc fraction to calculate the transition luminosities shows that the distributions of the luminosities for the transitions away from- and return to the powerlaw dominated state are both broad and appear to overlap. Finally we compare the measured X-ray luminosities with a small number of contemporaneous radio measurements. Overall this is the most comprehensive and uniform global study of black hole X-ray binaries to date.
In past decades a lot of progress has been made towards understanding the main s-process component that takes place in thermally pulsing Asymptotic Giant Branch (AGB) stars. During this process about half of the heavy elements, mainly between 90<=A<=209 are synthesized. Improvements were made in stellar modeling as well as in measuring relevant nuclear data for a better description of the main s process. The weak s process, which contributes to the production of lighter nuclei in the mass range 56<=A<=90 operates in massive stars (M>=8Msolar) and is much less understood. A better characterization of the weak s component would help disentangle the various contributions to element production in this region. For this purpose, a series of measurements of neutron-capture cross sections have been performed on medium-mass nuclei at the 3.7-MV Van de Graaff accelerator at FZK using the activation method. Also, neutron captures on abundant light elements with A<56 play an important role for s-process nucleosynthesis, since they act as neutron poisons and affect the stellar neutron balance. New results are presented for the (n,g) cross sections of 41K and 45Sc, and revisions are reported for a number of cross sections based on improved spectroscopic information.
Since the IUE satellite produced a vast collection of high-resolution UV spectra of central stars of planetary nebulae (CSPNe), there has not been any further systematic study of the stellar winds of these stars. The high spectral resolution, sensitivity and large number of archival observations in the FUSE archive allow the study of the stellar winds of CSPNe in the far UV domain where lines of species spanning a wide excitation range can be observed. We present here a preliminary analysis of the P Cygni profiles of a sample of 60 CSPNe observed by FUSE. P Cygni profiles evidencing fast stellar winds with velocities between 200 and 4,300 km/s have been found in 40 CSPNe. In many cases, this is the first time that fast stellar winds have been reported for these PNe. A detailed study of these far-UV spectra is on-going.
Theoretical arguments suggest that dust grains should grow in the dense cold parts of molecular clouds. Evidence for larger grains has so far been gathered in Near/Mid Infrared extinction and millimeter observations. Interpreting the data is, however, aggravated due to the complex interplay of density and dust properties (as well as temperature for thermal emission). We present new Spitzer data of L183 in bands sensitive and non-sensitive to PAHs. The visual extinction AV map derived in a former paper is fitted by a series of 3D Gaussian distribution. For different dust models, we calculate the scattered MIR radiation images of structures being in agreement with the AV map and compare them to the Spitzer data. The Spitzer data of L183 show emission in the 3.6 and 4.5 micron bands while the 5.8 micron band shows slight absorption. The emission layer of stochastically heated particles should coincide with the layer of strongest scattering of optical interstellar radiation which is seen as an outer surface on I band images different from the emission region seen in the Spitzer images. Moreover, PAH emission is expected to strongly increase from 4.5 to 5.8 micron which is not seen. Hence, we interpret this emission to be MIR cloudshine. Scattered light modeling assuming interstellar medium dust grains without growth does not reproduce flux measurable by Spitzer. On the contrary, models with grains growing with density yield images with a flux and pattern comparable to the Spitzer images in the bands 3.6, 4.5, and 8.0 micron.
Recent work on nearby AGNs has shown that X-ray variability is correlated with the mass and accretion rate onto the central SMBH. Here we present the application of the variability-luminosity relation to high redshift AGNs in the CDFS, making use of XMM-Newton observations. We use Montecarlo simulations in order to properly account for bias and uncertainties introduced by the sparse sampling and the very low statistics. Our preliminary results indicate that BH masses span over the range from 10^5 to 10^9 solar mass while accretion rates range from 10^-3 up to values greater than 1, in unit of Eddington accretion rate.
We present photometry of nine cataclysmic variable stars identified by the Sloan Digital Sky Survey, aimed at measuring the orbital periods of these systems. Four of these objects show deep eclipses, from which we measure their orbital periods. The light curves of three of the eclipsing systems are also analysed using the LCURVE code, and their mass ratios and orbital inclinations determined. SDSS J075059.97+141150.1 has an orbital period of 134.1564 +/- 0.0008 min, making it a useful object with which to investigate the evolutionary processes of cataclysmic variables. SDSS J092444.48+080150.9 has a period of 131.2432 +/- 0.0014 min and is probably magnetic. The white dwarf ingress and egress phases are very deep and short, and there is no clear evidence that this object has an accretion disc. SDSS J115207.00+404947.8 and SDSS J152419.33+220920.1 are nearly identical twins, with periods of 97.5 +/- 0.4 and 93.6 +/- 0.5 min and mass ratios of 0.14 +/- 0.03 and 0.17 +/- 0.03, respectively. Their eclipses have well-defined white dwarf and bright spot ingress and egress features, making them excellent candidates for detailed study. All four of the orbital periods presented here are shorter than the 2-3 hour period gap observed in the known population of cataclysmic variables.
CRESST-II, standing for Cryogenic Rare Events Search with Superconducting Thermometers phase II, is an experiment searching for Dark Matter. In the LNGS facility in Gran Sasso, Italy, a cryogenic detector setup is operated in order to detect WIMPs by elastic scattering off nuclei, generating phononic lattice excitations and scintillation light. The thermometers used in the experiment consist of a tungsten thin-film structure evaporated onto the CaWO4 absorber crystal. The process of evaporation causes a decrease in the scintillation light output. This, together with the need of a big-scale detector production for the upcoming EURECA experiment lead to investigations for producing thermometers on smaller crystals which are glued onto the absorber crystal. In our Run 31 we tested composite detectors for the first time in the Gran Sasso setup. They seem to produce higher light yields as hoped and could provide an additional time based discrimination mechanism for low light yield clamp events.
Magellanic Clouds are of extreme importance to the study of the star formation process in low metallicity environments. In this paper we report on the discovery of pre-main sequence candidates and young embedded stellar objects in N11 located in the Large Magellanic Cloud to cast light on the star formation scenario. We would like to remind that this comparison is complicated by the presence of a large age dispersion detected in the fields. Deep archive HST/ACS photometry is used to derive color-magnitude diagrams of the associations in N~11 and of the foreground field population. These data are complemented by archive IR Spitzer data which allow the detection of young embedded stellar objects. The spatial distribution of the pre-main sequence candidates and young embedded stellar objects is compared with literature data observed at different wavelengths, such as H$_{\alpha}$ and CO maps, and with the distribution of OB and Herbig Ae/Be stars. The degree of clustering is derived using the Minimal Spanning Tree method and the two point correlation function to get insights about the formation process. A large population of pre-main sequence candidates is found in N11. Their masses are in the range of 1.3-2 MSun for ages from 2 to 10 Myr. Young embedded stellar objects having ages of 0.1-1 Myr are found to be intermixed with the candidate pre-main sequence stars. The spatial distribution of the stars shows that this region is the product of clustered star formation. No significant difference is found in the clustering degree of young blue main sequence stars and faint pre-main sequence candidates, suggesting that they might be part of the same formation process. The data suggest that the star formation in the region is a long-lasting process where stars from 0.1 to 10 Myr are widely distributed.
The origin of the high inclination of Uranus' spin-axis (Uranus' obliquity) is one of the great unanswered questions about the Solar system. Giant planets are believed to form with nearly zero obliquity, and it has been shown that the present behaviour of Uranus' spin is essentially stable. Several attempts were made in order to solve this problem. Here we report numerical simulations showing that Uranus' axis can be tilted during the planetary migration, without the need of a giant impact, provided that the planet had an additional satellite and a temporary large inclination. This might have happened during the giant planet instability phase described in the Nice model. In our scenario, the satellite is ejected after the tilt by a close encounter at the end of the migration. This model can both explain Uranus' large obliquity and bring new constraints on the planet orbital evolution.
A front end ASIC (BiCMOS-SiGe 0.35 um) has been developed within the framework of the MIMAC detector project, which aims at directional detection of non-baryonic Dark Matter. This search strategy requires 3D reconstruction of low energy (keV) tracks with a gazeous uTPC. The development of this front end ASIC is a key point in this project, allowing the 3D track reconstruction. Each ASIC monitors 16 strips of pixels with charge preamplifiers and their time over threshold is provided in real time by current discriminators via two serializing LVDS links working at 320 MHz. The charge is summed over the 16 strips and provided via a shaper. These specifications have been chosen in order to build an auto triggered electronic. An acquisition board and the related software were developed in order to validate this methodology on a prototype chamber. The prototype detector presents an anode where 2x96 strips are monitored.
Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short time scale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (omega Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age4,5. Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron content and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.
A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.
X-ray sources with very few counts can be identified with low-noise X-ray detectors such as ACIS onboard the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broad-band X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high S/N spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M17 HII region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of non-linear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic AGN.
Phased array feeds (PAFs) for reflector antennas offer the potential for increased reflector field of view and faster survey speeds. To address some of the development challenges that remain for scientifically useful PAFs, including calibration and beamforming algorithms, sensitivity optimization, and demonstration of wide field of view imaging, we report experimental results from a 19 element room temperature L-band PAF mounted on the Green Bank 20-Meter Telescope. Formed beams achieved an aperture efficiency of 69% and system noise temperature of 66 K. Radio camera images of several sky regions are presented. We investigate the noise performance and sensitivity of the system as a function of elevation angle with statistically optimal beamforming and demonstrate cancelation of radio frequency interference sources with adaptive spatial filtering.
The anticipated high sensitivity and the science goals of the next generation X-ray space missions, like the International X-ray Observatory or Simbol-X, rely on a low instrumental background, which in turn requires optimized shielding concepts. We present Geant4 based simulation results on the IXO Wide Field Imager cosmic ray proton induced background in comparison with previous results obtained for the Simbol-X LED and HED focal plane detectors. Our results show that an improvement in mean differential background flux compared to actually operating X-ray observatories may be feasible with detectors based on DEPFET technology. In addition we present preliminary results concerning the validation of Geant4 based radioactive decay simulation in space applications as a part of the Nano5 project.
3D Magnetohydrodynamic simulations show that when matter accretes onto neutron stars, in particular if the misalignment angle is small, it does not constantly fall at a fixed spot. Instead, the location at which matter reaches the star moves. These moving hot spots can be produced both during stable accretion, where matter falls near the magnetic poles of the star, and unstable accretion, characterized by the presence of several tongues of matter which fall on the star near the equator, due to Rayleigh-Taylor instabilities. Precise modeling with Monte Carlo simulations shows that those movements could be observed as high frequency Quasi Periodic Oscillations. We performed a number of new simulation runs with a much wider set of parameters, focusing on neutron stars with a small misalignment angle. In most cases we observe oscillations whose frequency is correlated with the mass accretion rate $\dot{M}$. Moreover, in some cases double QPOs appear, each of them showing the same correlation with $\dot{M}$.
(Abridged) X-ray observations of clusters of galaxies reveal the presence of edges in surface brightness and temperature, known as ``cold fronts''. In relaxed clusters with cool cores, these commonly observed edges have been interpreted as evidence for the "sloshing" of the core gas in the cluster's gravitational potential. Such sloshing may provide a source of heat to the cluster core by mixing hot gas from the cluster outskirts with the cool core gas. Using high-resolution $N$-body/Eulerian hydrodynamics simulations, we model gas sloshing in galaxy clusters initiated by mergers with subclusters. The simulations include merger scenarios with gas-filled and gasless subclusters. The effect of changing the viscosity of the intracluster medium is also explored. We find that sloshing can facilitate heat inflow to the cluster core, provided that there is a strong enough disturbance. In adiabatic simulations, we find that sloshing can raise the entropy floor of the cluster core by nearly an order of magnitude in the strongest cases. If the ICM is viscous, the mixing of gases with different entropies is decreased and consequently the heat flux to the core is diminished. In simulations where radiative cooling is included, we find that though eventually a cooling flow develops, sloshing can prevent the significant buildup of cool gas in the core for times on the order of a Gyr for small disturbances and a few Gyr for large ones. If repeated encounters with merging subclusters sustain the sloshing of the central core gas as is observed, this process can provide a relatively steady source of heat to the core, which can help to prevent a significant cooling flow.
We use WIYN High-resolution Infrared Camera (WHIRC) H (1.6 micron) band imaging, archival Spitzer, HST, and GALEX data, simulations and data from the literature to argue for the presence of a strong end-on bar in nearby spiral galaxy NGC 6503. The evidence consists of both photometric and kinematic signatures as well as resonant structures present in the galaxy which are most often associated with bars. These include a central peak followed by a plateau in the surface brightness profile, an extreme decrement in the central stellar velocity dispersion (a sigma-drop), and the presence of an inner ring as well as a circumnuclear disk with spiral structure. In this framework the previously identified nuclear star-forming ring is instead a young inner ring spanned in diameter by the strong end-on bar.
The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in
August/September 2005, which reached a maximum X-ray flux of 400mCrab in the
5-100keV range. The outburst was observed by INTEGRAL and RXTE. The energy of
the fundamental cyclotron line has been measured with INTEGRAL and RXTE at
~45keV. Flaring activity was observed during the rise to the peak of the
outburst. RXTE observations during one of these flares found the energy of the
fundamental cyclotron line shifted to a significantly higher position than
during the rest of the outburst, where it remains constant. Also, the
energy-dependent pulse profiles during the flare differ significantly from the
rest of the outburst. These differences have been interpreted with the presence
of magnetospheric instabilities at the onset of the accretion.
A decomposition method is applied to A 0535+26 pulse profiles. Basic
assumptions of the method are that the asymmetry observed in the pulse profiles
is caused by a distorted magnetic dipole field, and that the emission regions
have axisymmetric beam patterns. Using pulse profiles obtained from RXTE
observations, the contribution of the two emission regions has been
disentangled. Constraints on geometry of the pulsar and a possible solution of
the beam pattern are given. First results of the comparison of the
reconstructed beam pattern with a geometrical model that includes relativistic
light deflection are presented.
We obtain modified dispersion relations by requiring the vanishing of determinant of inverse of modified photon propagators in Lorentz invariance violation (LIV) theory. Inspired by these dispersion relations, we give a more general dispersion relation with less assumption and apply it to the recent observed gamma-ray burst GRB090510 to extract various constraints on LIV parameters. We find that the constraint on quantum gravity mass is slightly larger than the Planck mass but is consistent with the other recent observations, so the corresponding LIV coefficient $\xi_1$ has reached the natural order ($o(1)$) as one expects. From our analysis, the linear LIV corrections to photon group velocity might be not excluded yet.
We investigate the leptophilic properties of Dirac gauginos in an R--symmetric N=2 supersymmetric model with extended gauge and Higgs sectors. The annihilation of Dirac gauginos to leptons requires no chirality flip in the final states so that it is not suppressed as in the Majorana case. This implies that it can be sizable enough to explain the positron excess observed by the PAMELA experiment with moderate or no boost factors. When squark masses are heavy, the annihilation of Dirac gauginos to hadrons is controlled by their Higgsino fraction and is driven by the $hZ$ and $W^+W^-$ final states. Moreover, at variance with the Majorana case, Dirac gauginos with a non-vanishing higgsino fraction can also have a vector coupling with the $Z$ gauge boson leading to a sizable spin--independent scattering cross section off nuclei. Saturating the current antiproton limit, we show that Dirac gauginos can leave a signal in direct detection experiments at the level of the sensitivity of dark matter searches at present and in the near future.
We expand the superpotential of $\nu$MSSM to 6th order. This is the order at which all flat directions can be lifted. All 5179 couplings are independent ie. the superpotential cannot be zero for all fields, without all couplings being zero. Likewise, any gauge invariant potential to the 6th order can be made by fixing the constants. A specific and welldefined choice of normalisation has been adopted. The case for investigating this potential, rather than looking at one or several generalised flat directions is made.
We find suitable potentials in the multiple scalar fields scenario by using the Noether symmetry approach. We discussed three models with multiple scalar fields: N-quintessence with positive kinetic terms, N-phantom with negative kinetic terms and N-quintom with both positive and negative kinetic terms. In the N-quintessence case, the exponential potential which could be derived from several theoretic models is obtained from the Noether conditions. In the N-phantom case, the potential $(V_0/2)(1-\cos(\sqrt{3N/2}(\phi/m_{pl})))$, which could be derived from the Pseudo Nambu-Goldstone boson model, is chosen as the Noether conditions required. In the N-quintom case, we derive a relation $DV'_{q}=-\tilde{D}V'_{p}$ between the potential forms for the quintessence-like fields and the phantom-like fields by using the Noether symmetry.
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We report on the first Suzaku observation of IGR J16318-4848, the most
extreme example of a new group of highly absorbed X-ray binaries that have
recently been discovered by the International Gamma-Ray Astrophysics Laboratory
INTEGRAL. The Suzaku observation was carried out between 2006 August 14 and 17,
with a net exposure time of 97 ks.
The average X-ray spectrum of the source can be well described with a
continuum model typical for neutron stars i.e., a strongly absorbed power law
continuum with a photon index of 0.676(42) and an exponential cutoff at 20.5(6)
keV. The absorbing column is 1.95(3)x10e24 cm-2. Consistent with earlier work,
strong fluorescent emission lines of Fe Kalpha, Fe Kbeta, and Ni Kalpha are
observed. Despite the large absorbing column, no Compton shoulder is seen in
the lines, arguing for a non-spherical and inhomogeneous absorber.
Seen at an average 5-60 keV absorbed flux of 3.4x10e-10 erg cm-2 s-1, the
source exhibits significant variability on timescales of hours.
We use 10 orbits of Advanced Camera for Surveys observations to reach the end of the white dwarf cooling sequence in the solar-metallicity open cluster NGC 2158. Our photometry and completeness tests show that the end falls at magnitude m_F606W = 27.5 +/- 0.15, which implies an age between ~1.8 and ~2.0 Gyr, consistent with the age of 1.9 +/- 0.2 Gyr obtained from fits to the main-sequence turn-off. The faintest white dwarfs show a clear turn toward bluer colors, as predicted by theoretical isochrones.
The environment is known to affect the formation and evolution of galaxies considerably best visible through the well-known morphology-density relationship. In this paper we study the effect of environment on the evolution of early-type galaxies by analysing the stellar population properties of 3,360 galaxies morphologically selected by visual inspection from the SDSS in the redshift range 0.05<z<0.06. We find that the distribution of ages is bimodal with a strong peak at old ages and a secondary peak at young ages around ~ 2.5Gyr containing about 10 per cent of the objects. This is analogue to 'red sequence' and 'blue cloud' identified in galaxy populations usually containing both early and late type galaxies. The fraction of the young, rejuvenated galaxies increases with both decreasing galaxy mass and decreasing environmental density up to about 45 per cent. The rejuvenated galaxies have lower alpha/Fe ratios than the average and most of them show signs of ongoing star formation through their emission line spectra. All objects that host AGN in their centres without star formation are part of the red sequence population. We confirm and statistically strengthen earlier results that luminosity weighted ages, metallicities, and alpha/Fe element ratios of the red sequence population correlate well with velocity dispersion and galaxy mass. Most interestingly, however, these scaling relations are not sensitive to environmental densities and are only driven by galaxy mass. We infer that early-type galaxy formation has undergone a phase transition a few billion years ago around z~0.2. A self-regulated formation phase without environmental dependence has recently been superseded by a rejuvenation phase, in which the environment plays a decisive role possibly through galaxy interactions.
An 8.8 solar mass electron-capture supernova (SN) was simulated in spherical symmetry consistently from collapse through explosion to nearly complete deleptonization of the forming neutron star. The evolution time of about 9 s is short because of nucleon-nucleon correlations in the neutrino opacities. After a brief phase of accretion-enhanced luminosities (~200 ms), luminosity equipartition among all species becomes almost perfect and the spectra of electron antineutrinos and muon/tau antineutrinos very similar. We discuss consequences for the neutrino-driven wind as a nucleosynthesis site and for flavor oscillations of SN neutrinos.
Large-scale structure projections are an obstacle in converting the shear signal of clusters detected in weak-lensing maps into virial masses. However, this step is not necessary for constraining cosmology with the shear-peak abundance, if we are able to predict its amplitude. We generate a large ensemble of N-body simulations spanning four cosmological models, with total volume V~1 (Gpc/h)^3 per model. Variations to the matter density parameter and amplitude of fluctuations are considered. We measure the abundance of peaks in the mass density projected in ~100 Mpc/h slabs to determine the impact of structures spatially correlated with the simulation clusters, identified by the 3D friends-of-friends algorithm. The halo model shows that the choice of the smoothing filter for the density field is important in reducing the contribution of correlated projections to individual halo masses. Such contributions are less than 2% in the case of the optimal, compensated filter used throughout this analysis. We measure the change in the mass of peaks when projected in slabs of various thicknesses. Peaks in slabs of 26 Mpc/h and 102 Mpc/h suffer an average mass change of less than 2% compared to their mass in slabs of 51 Mpc/h. We then explore the cosmology dependence of the projected-peak mass function, and find that, for a wide range of slab thicknesses (<500 Mpc/h), it scales with cosmology in exactly the same way as the 3D friends-of-friends mass function and the Sheth-Tormen formula. This extends the earlier result of Marian et al. (2009). Finally, we show that for all cosmological models considered, the low and intermediate mass bins of the peak abundance can be described using a modified Sheth-Tormen functional form to within 10%-20% accuracy.
SN 2006bt displays characteristics unlike those of any other known Type Ia supernova (SN Ia). We present optical light curves and spectra of SN 2006bt which demonstrate the peculiar nature of this object. SN 2006bt has broad, slowly declining light curves indicative of a hot, high-luminosity SN, but lacks a prominent second maximum in the i band as do low-luminosity SNe Ia. Its spectra are similar to those of low-luminosity SNe Ia, containing features that are only present in cool SN photospheres. Light-curve fitting methods suggest that SN 2006bt is reddened by a significant amount of dust; however, it occurred in the outskirts of its early-type host galaxy and has no strong Na D absorption in any of its spectra, suggesting a negligible amount of host-galaxy dust absorption. C II is possibly detected in our pre-maximum spectra, but at a much lower velocity than other elements. The progenitor was likely very old, being a member of the halo population of a galaxy that shows no signs of recent star formation. SNe Ia have been very successfully modeled as a one-parameter family, and this is fundamental to their use as cosmological distance indicators. SN 2006bt is a challenge to that picture, yet its relatively normal light curves allowed SN 2006bt to be included in cosmological analyses. We generate mock SN Ia datasets which indicate that contamination by similar objects will both increase the scatter of a SN Ia Hubble diagram and systematically bias measurements of cosmological parameters. However, spectra and rest-frame i-band light curves should provide a definitive way to identify and eliminate such objects.
At energies above a few TeV, no measurements of the cosmic-ray electron spectrum exist yet. By considering the similarity of air showers induced by electrons and gamma rays as seen by ground-based arrays, we use published limits on isotropic gamma-ray fluxes to place first constraints on the >10 TeV electron spectrum. We demonstrate that, due the proximity of known sources, the flux of such electrons (and positrons) can be large. We show how these smoothly connect to lower-energy positrons measured by PAMELA and relate to exciting new indications from Fermi.
We present a minimally-parametric reconstruction of the primordial power spectrum using the most recent cosmic microwave background and large scale structure data sets. Our goal is to constrain the shape of the power spectrum while simultaneously avoiding strong theoretical priors and over-fitting of the data. We find no evidence for any departure from a power law spectral index. We also find that an exact scale-invariant power spectrum is disfavored by the data, but this conclusion is weaker than the corresponding result assuming a theoretically-motivated power law spectral index prior. The reconstruction shows that better data are crucial to justify the adoption of such a strong theoretical prior observationally. These results can be used to determine the robustness of our present knowledge when compared with forthcoming precision data from Planck.
Abridge-A detection or nondetection of primordial non-Gaussianity by using the CMB data is crucial not only to discriminate inflationary models but also to test alternative scenarios. Non-Gaussianity offers, therefore, a powerful probe of the physics of the primordial universe. The extraction of primordial non-Gaussianity is a difficult enterprise since several effects of non-primordial nature can produce non-Gaussianity. Most of the Gaussianity analyses of CMB data have been performed by using part-sky frequency, where the mask are used to deal with the galactic diffuse foreground emission. However, full-sky map seems to be potentially more appropriate to test for Gaussianity of the CMB data. On the other hand, masks can induce bias in some non-Gaussianity analyses. Here we use two recent large-angle non-Gaussianity indicators, based on skewness and kurtosis of large-angle patches of CMB maps, to examine the question of non-Gaussianity in the available full-sky five-year WMAP maps. We show that these full-sky foreground-reduced maps present a significant deviation from Gaussianity of different levels, which vary with the foreground-reducing procedures. We also make a Gaussianity analysis of the foreground-reduced five-year WMAP maps with a \emph{KQ75} mask, and compare with the similar analysis performed with the full-sky foreground-reduced maps. This comparison shows a significant reduction in the levels of non-Gaussianity when the mask is employed, which provides indications on the suitability of the foreground-reduced maps as Gaussian reconstructions of the full-sky CMB.
We combine SAURON integral field data of a representative sample of local early-type, red sequence galaxies with Spitzer/IRAC imaging in order to investigate the presence of trace star formation in these systems. With the Spitzer data, we identify galaxies hosting low-level star formation, as traced by PAH emission, with measured star formation rates that compare well to those estimated from other tracers. This star formation proceeds according to established scaling relations with molecular gas content, in surface density regimes characteristic of disk galaxies and circumnuclear starbursts. We find that star formation in early-type galaxies happens exclusively in fast-rotating systems and occurs in two distinct modes. In the first, star formation is a diffuse process, corresponding to widespread young stellar populations and high molecular gas content. The equal presence of co- and counter-rotating components in these systems strongly implies an external origin for the star-forming gas, and we argue that these star formation events may be the final stages of (mostly minor) mergers that build up the bulges of red sequence lenticulars. In the second mode of star formation, the process is concentrated into well-defined disk or ring morphologies, outside of which the host galaxies exhibit uniformly evolved stellar populations. This implies that these star formation events represent rejuvenations within previously quiescent stellar systems. Evidence for earlier star formation events similar to these in all fast rotating early-type galaxies suggests that this mode of star formation may be common to all such galaxies, with a duty cycle of roughly 1/10, and likely contributes to the embedded, co-rotating inner stellar disks ubiquitous in this population.
Following our study on the incidence, morphology and kinematics of the ionised gas in early-type galaxies we now address the question of what is powering the observed nebular emission. To constrain the likely sources of gas excitation, we resort to a variety of ancillary data, draw from complementary information on the gas kinematics, stellar populations and galactic potential from the SAURON data, and use the SAURON-specific diagnostic diagram juxtaposing the [OIII]/Hb and [NI]/Hb line ratios. We find a tight correlation between the stellar surface brightness and the flux of the Hb recombination line across our sample, which points to a diffuse and old stellar source as the main contributor of ionising photons in early-type galaxies, with post-asymptotic giant branch (pAGB) stars being still the best candidate based on ionising-balance arguments. Other ionising sources such as a central AGN, OB-stars, shocks or the interaction between the hot and warm phases of the interestellar medium are found to play only a limited or localised role in powering the diffuse nebular emission observed in our sample galaxies. These results lead us to investigate the relative importance of stellar and AGN photoionisation in explaining the ionised-gas emission observed in early-type galaxies by the Sloan Digital Sky Survey (SDSS). By simulating how our sample galaxies would appear if placed at further distance and targeted by the SDSS, we conclude that only in very few, if any, of the SDSS early-type galaxies that display modest values for the equivalent width of the [OIII] line (less than ~2.4\AA) and LINER-like [OIII]/Hb values, the nebular emission is truly powered by an AGN.
We present discovery imaging and spectroscopy for nine new z ~ 6 quasars found in the Canada-France High-z Quasar Survey (CFHQS) bringing the total number of CFHQS quasars to 19. By combining the CFHQS with the more luminous SDSS sample we are able to derive the quasar luminosity function from a sample of 40 quasars at redshifts 5.74 < z < 6.42. Our binned luminosity function shows a slightly lower normalisation and flatter slope than found in previous work. The binned data also suggest a break in the luminosity function at M_1450 approx -25. A double power law maximum likelihood fit to the data is consistent with the binned results. The luminosity function is strongly constrained (1 sigma uncertainty < 0.1 dex) over the range -27.5 < M_1450 < -24.7. The best-fit parameters are Phi(M_1450^*) = 1.14 x 10^-8 Mpc^-3 mag^-1, break magnitude M_1450^* = -25.13 and bright end slope beta = -2.81. However the covariance between beta and M_1450^* prevents strong constraints being placed on either parameter. For a break magnitude in the range -26 < M_1450^* < -24 we find -3.8 < beta < -2.3 at 95% confidence. We calculate the z = 6 quasar intergalactic ionizing flux and show it is between 20 and 100 times lower than that necessary for reionization. Finally, we use the luminosity function to predict how many higher redshift quasars may be discovered in future near-IR imaging surveys.
We present results from the mid-infrared spectral mapping of Stephan's Quintet using the Spitzer Space Telescope. A 1000 km/s collision has produced a group-wide shock and for the first time the large-scale distribution of warm molecular hydrogen emission is revealed, as well as its close association with known shock structures. In the main shock region alone we find 5.0 $\times10^{8}$ M$_{\odot}$ of warm H$_2$ spread over $\sim$ 480 kpc$^2$ and additionally report the discovery of a second major shock-excited H$_2$ feature. This brings the total H$_2$ line luminosity of the group in excess of 10$^42$ erg/s. In the main shock, the H$_2$ line luminosity exceeds, by a factor of three, the X-ray luminosity from the hot shocked gas, confirming that the H$_2$-cooling pathway dominates over the X-ray. [Si II]34.82$\mu$m emission, detected at a luminosity of 1/10th of that of the H$_2$, appears to trace the group-wide shock closely and in addition, we detect weak [FeII]25.99$\mu$m emission from the most X-ray luminous part of the shock. Comparison with shock models reveals that this emission is consistent with regions of fast shocks (100 < $V_{s}$ < 300 km/s) experiencing depletion of iron and silicon onto dust grains. Star formation in the shock (as traced via ionic lines, PAH and dust emission) appears in the intruder galaxy, but most strikingly at either end of the radio shock. The shock ridge itself shows little star formation, consistent with a model in which the tremendous H$_{2}$ power is driven by turbulent energy transfer from motions in a post-shocked layer. The significance of the molecular hydrogen lines over other measured sources of cooling in fast galaxy-scale shocks may have crucial implications for the cooling of gas in the assembly of the first galaxies.
When cosmic structures form, they grow in mass via accretion from their surrounding environment. The energy associated with this transport of material provides a ubiquitous source of internal turbulence. We propose that accretion will drive turbulent motions in a wide range of astrophysical objects and study this process in the case of galaxies, molecular clouds and protoplanetary disks. We use a combination of numerical simulations and analytical arguments to predict the level of turbulence as a function of the accretion rate, the dissipation scale, and the density contrast, and compare with observational data. We find that in Milky Way type galaxies the turbulence in the non star-forming outer parts of the disk can be explained by accretion, provided that the galaxies accrete at a rate comparable to the rate at which they form stars. We note that the extended outer disk carries the bulk of the turbulent energy in the galaxy. Our approach fails for dwarf galaxies and we expect other sources to dominate. We calculate the rate at which molecular clouds grow in mass when they build up from the atomic component of the galactic gas. The very process of cloud formation can drive turbulent motions on small scales via establishing the turbulent cascade. In the case of T-Tauri disks, we show that accretion can drive subsonic turbulence at the observed level if the rate at which gas falls onto the disk is comparable to the rate at which disk material accretes onto the central star. This also explains the observed relation of accretion rate and stellar mass, dM/dt ~ M^1.8. The efficiency required to convert infall motion into turbulence is of order of a few percent in all three cases. We conclude that accretion-driven turbulence is a universal concept with far-reaching implications for a wide range of astrophysical objects.
(Abridged) We studied an exceptional period of activity of the anomalous X-ray pulsar 1E 1547.0-5408 in January 2009, during which about 200 bursts were detected by INTEGRAL. The major activity episode happened when the source was outside the field of view of all the INTEGRAL instruments. But we were still able to study the properties of 84 bursts detected simultaneously by the anti-coincidence shield of the spectrometer SPI and by the detector of the imager ISGRI. We find that the luminosity of the 22 January 2009 bursts of 1E 1547.0-5408 was > 1e42 erg/s. This luminosity is comparable to that of the bursts of soft gamma repeaters (SGR) and is at least two orders of magnitude larger than the luminosity of the previously reported bursts from AXPs. Similarly to the SGR bursts, the brightest bursts of 1E 1547.0-5408 consist of a short spike of ~100 ms duration with a hard spectrum, followed by a softer extended tail of 1-10 s duration, which occasionally exhibits pulsations with the source spin period of ~2 s. The observation of AXP bursts with luminosities comparable to the one of SGR bursts strengthens the conjecture that AXPs and SGRs are different representatives of one and the same source type.
We perform a semi-automated survey for tau>=2 Lyman Limit systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey, Data Release 7. From a starting sample of 2473 quasars with zem=3.6-4.4, we analyze 469 spectra meeting strict seletion criteria for a total redshift path Dz=93.8 and identify 192 intervening systems at z>3.3. The incidence of tau>=2 LLSs per unit redshift, l(z), is well described by a single-power law at these redshifts: l(z) = C_LLS [(1+z)/(1+z_*)]^gamma, with z_*=3.7, C_LLS = 1.9+/-0.2, and gamma = 5.2+/-1.5 (68% c.l.). These values are systematically lower than previous estimates (especially at z<4) but are consistent with recent measurements of the mean free path to ionizing radiation. Extrapolations of this power-law to z=0 are inconsistent with previous estimations of l(z) at z<1 and suggest a break at z~2, similar to that observed for the Lya forest. Our results also indicate that the systems giving rise to LLS absorption decrease by ~50% in comoving number density and/or physical size from z=4 to 3.3, perhaps due to an enhanced extragalactic ultraviolet background. The observations place an integral constraint on the HI frequency distribution f(N_HI,X) and indicate that the power-law slope beta= dln[f(N,X)]/dln[N] is likely shallower than beta = -1 at N_HI=10^18 cm^-2. Including other constraints on f(N_HI,X) from the literature, we infer that beta is steeper than beta = -1.7 at N_HI~10^15 cm^-2, implying at least two inflections in f(N_HI,X). We also perform a survey for proximate LLSs (PLLSs) and find that l(z)_PLLS is systematically lower ~25% than intervening systems. Finally, we estimate that systematic effects impose an uncertainty of 10-20% in the l(z) measurements; these effects may limit the precision of all future surveys.
We present an absorption line analysis of the Lyman limit system (LLS) at z=3.55 in our Magellan/MIKE spectrum of PKS2000-330. Our analysis of the Lyman limit and full HI Lyman series constrains the total HI column density of the LLS (N_HI = 10^[18.0 +/- 0.25] cm^{-2} for b_HI >= 20 km/s) and also the N_HI values of the velocity subsystems comprising the absorber. We measure ionic column densities for metal-line transitions associated with the subsystems and use these values to constrain the ionization state (>90% ionized) and relative abundances of the gas. We find an order of magnitude dispersion in the metallicities of the subsystems, marking the first detailed analysis of metallicity variations in an optically thick absorber. The results indicate that metals are not well mixed within the gas surrounding high $z$ galaxies. Assuming a single-phase photoionization model, we also derive an N_H-weighted metallicity, <[Si/H]> = -1.66 +/- 0.25, which matches the mean metallicity in the neutral ISM in high z damped Lya systems (DLAs). Because the line density of LLSs is ~10 times higher than the DLAs, we propose that the former dominate the metal mass-density at z~3 and that these metals reside in the galaxy/IGM interface. Considerations of a multi-phase model do not qualitatively change these conclusions. Finally, we comment on an anomalously large O^0/Si^+ ratio in the LLS that suggests an ionizing radiation field dominated by soft UV sources (e.g. a starburst galaxy). Additional abundance analysis is performed on the super-LLS systems at z=3.19.
We present new Green Bank Telescope (GBT) 21 cm neutral hydrogen (HI)
observations of a complete distance limited sample of 22 Hickson Compact Groups
(HCGs) with at least four true members. We detected an average HI mass of $8
\times 10^{9} M_{\odot}$ (median= $6\times 10^{9} M_{\odot}$), which is
significantly larger than previous single-dish measurements. Consequently, the
HI-deficiencies for these HCGs have been reduced, although not completely
eliminated. Spectral comparison of the GBT data with complementary Very Large
Array (VLA) data shows significant HI excess in the GBT spectra. The observed
excess is primarily due to the high surface brightness sensitivity of the GBT
detecting diffuse, low column density HI in these groups. % high surface
brightness sensitivity of the GBT, although in a few cases spatial filtration
by the VLA is also plausible. The excess gas forms a faint diffused neutral
medium which is an intermediate stage in the evolution of high-surface
brightness HI tidal debris in the intra-group medium (IGM) before it is fully
ionized. The excess gas mass fraction (ratio of excess HI to total HI) for our
complete sample varies from 5% to 81% with an average of 36% (median=30%). The
excess gas mass fraction is highest in slightly HI deficient groups where the
tidal debris has had enough time to evolve. We also find the excess gas content
increases with the evolutionary phase of the group described in
Verdes-Montenegro et al. 2001.
Theoretical calculations indicate that an HI cloud of radius >200 pc would
survive in an IGM of 2 million Kelvin for more than the typical dynamical
lifetime of a group. However, smaller clouds get evaporated and assimilated
into the hot IGM in a much shorter timescale.
The metallicities implied by collisionally excited lines (CELs) of heavy elements in H II regions are systematically lower than those implied by recombination lines (RLs) by factors ~2, introducing uncertainties of the same order in the metallicities inferred for the interstellar medium of any star-forming galaxy. Most explanations of this discrepancy are based on the different sensitivities of CELs and RLs to electron temperature, and invoke either some extra heating mechanism producing temperature fluctuations in the ionized region or the addition of cold gas in metal-rich inclusions or ionized by cosmic rays or X rays. These explanations will change the temperature structure of the ionized gas from the one predicted by simple photoionization models and, depending on which one is correct, will imply different metallicities for the emitting gas. We select nine H II regions with observed spectra of high quality and show that simple models with metallicities close to the ones implied by oxygen CELs reproduce easily their temperature structure, measured with Te([N II])/Te([O III]), and their oxygen CELs emission. We discuss the strong constraints that this agreement places on the possible explanations of the discrepancy and suggest that the simplest explanation, namely errors in the line recombination coefficients by factors ~2, might be the correct one. In such case, CELs will provide the best estimates of metallicity.
In this paper, after briefly reviewing the theory of vectorial vortices, we describe our technological approach to generating the necessary phase helix, and report results obtained with the first optical vectorial vortex coronagraph (OVVC) in the laboratory. To implement the geometrical phase ramp, we make use of Liquid Crystal Polymers (LCP), which we believe to be the most efficient technological path to quickly synthesize optical vectorial vortices of virtually any topological charge. With the first prototype device of topological charge 2, a maximum peak-to-peak attenuation of 1.4e-2 and a residual light level of 3e-5 at an angular separation of 3.5 l/d (at which point our current noise floor is reached) have been obtained at a wavelength of 1.55 microns. These results demonstrate the validity of using space-variant birefringence distributions to generate a new family of coronagraphs usable in natural unpolarized light, opening a path to high performance coronagraphs that are achromatic and have low-sensitivity to low-order wavefront aberrations.
A galaxy's metallicity provides a record of star formation, gas accretion, and gas outflow, and is therefore one of the most informative measurements that can be made at high redshift. It is also one of the most difficult. I review methods of determining chemical abundances in distant star-forming galaxies, and summarize results for galaxies at 1<z<3. I then focus on the mass-metallicity relation, its evolution with redshift, and its uses in constraining inflows and outflows of gas, and conclude with a brief discussion of future prospects for metallicity measurements at high redshift.
The GeV light curve of a pulsar is an important probe to detect acceleration regions in its magnetosphere. Motivated by the recent reports on the observations of pulsars by {\it Fermi} Large Area Telescope (LAT), we restudy the two-pole caustic model and revise it to investigate the properties of the light curves in the GeV band. In the revised model, although acceleration gaps can extend from the star surface to the light cylinder along near the last open field lines, the extension of the gaps along the azimuthal direction is limited because of photon-photon pair production process. In such gaps, high-energy photons are emitted uniformly and tangentially to the field lines but cannot be efficiently produced along these field lines where the distances to the null charge surface are larger than $\sim0.9$ times of the distance of the light cylinder, and the effective azimuth extension of the gaps is about $230^\circ$. The model is applied to the four pulsars Vela, PSR J1028-5819, PSR J0205+6449, and PSR J2021+3651 whose light curves obtained with {\it Fermi} have been recently released. The model is successful in reproducing the general feature of the light curves for the four pulsars, and the radial distances of the radio pulse for the four pulsars are estimated.
We perform a non-radial adiabatic perturbation analysis on homologous conventional polytropic stellar core collapses. The core collapse features a polytropic exponent $\Gamma=4/3$ relativistic gas under self-gravity of spherical symmetry while three-dimensional perturbations involve an adiabatic exponent $\gamma$ with $\gamma\neq\Gamma$ such that the Brunt-V$\ddot{\rm a}$is$\ddot{\rm a}$l$\ddot{\rm a}$ buoyancy frequency ${\cal N}$ does not vanish. With proper boundary conditions, we derive eigenvalues and eigenfunctions for different modes of oscillations. In reference to stellar oscillations and earlier results, we examine behaviours of different modes and the criterion for instabilities. The acoustic p$-$modes and surface f$-$modes remain stable. For $\gamma<\Gamma$, convective instabilities appear as unstable internal gravity g$^{-}-$modes. For $\gamma>\Gamma$, sufficiently low-order internal gravity g$^{+}-$modes are stable, whereas sufficiently high-order g$^{+}-$modes, which would have been stable in a static star, become unstable during self-similar core collapses. For supernova explosions, physical consequences of such inevitable g$-$mode instabilities are speculated.
We present a study of the star cluster formation in M51 based on the image data taken with Advanced Camera for Surveys (ACS) and Wide Field Planetary Camera 2 (WFPC2) of Hubble Space Telescope (HST). We have derived the star cluster formation rate using the ages and masses of about 2,000 star clusters estimated by comparing photometric data (F336W, F435W, F555W, and F814W) with theoretical population synthesis models. The star cluster formation rate increased significantly during the period of 100 ~ 250 Myr ago. This period roughly coincides with the epoch of dynamical encounters of two galaxies, NGC 5194 and NGC 5195, expected by theoretical models. The age distribution of the star clusters also shows two peaks at about 100 Myr and 250 Myr ago. The star cluster mass ranges from 10^3 to 10^6 M_{\odot} and the mass function can be represented by a power law with an index ranging from \alpha = -2.23 \pm 0.34 for t<10 Myr to \alpha = -1.37 \pm 0.11 for t>100 Myr. The mass function of star clusters older than 10 Myr also appears to display the steepest distribution with \alpha \approx -1.50 at around 200 Myr ago, near the expected epoch of the galaxy interaction. We also confirm the correlations of cluster size increasing with cluster mass (with a best fit slope of 0.16 \pm 0.02), and with cluster age (0.14 \pm 0.03).
We present chemical abundances of 57 metal-poor stars that are likely constituents of the outer stellar halo in the Milky Way. Almost all of the sample stars have an orbit reaching a maximum vertical distance (Z_max) of >5 kpc above and below the Galactic plane. High-resolution, high signal-to-noise spectra for the sample stars obtained with Subaru/HDS are used to derive chemical abundances of Na, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y and Ba with an LTE abundance analysis code. The resulting abundance data are combined with those presented in literature that mostly targeted at smaller Z_max stars, and both data are used to investigate any systematic trends in detailed abundance patterns depending on their kinematics. It is shown that, in the metallicity range of -2<[Fe/H]<-1, the [Mg/Fe] ratios for the stars with Z_max>5 kpc are systematically lower (~0.1 dex) than those with smaller Z_max. This result of the lower [alpha/Fe] for the assumed outer halo stars is consistent with previous studies that found a signature of lower [alpha/Fe] ratios for stars with extreme kinematics. A distribution of the [Mg/Fe] ratios for the outer halo stars partly overlaps with that for stars belonging to the Milky Way dwarf satellites in the metallicity interval of -2<[Fe/H]<-1 and spans a range intermediate between the distributions for the inner halo stars and the stars belonging to the satellites. Our results confirm inhomogeneous nature of chemical abundances within the Milky Way stellar halo depending on kinematic properties of constituent stars as suggested by earlier studies. Possible implications for the formation of the Milky Way halo and its relevance to the suggested dual nature of the halo are discussed.
Recently, the distribution of velocity dispersion as far as 400kpc around red isolated galaxies was derived from statistical studies of satellites in the SDSS (Klypin & Prada 2009). This could help to constrain dark matter models at intermediate scales. We compare the predictions of different DM distributions, LCDM with NFW or cored profiles, and also modified gravity models, with observations. It is shown how the freedom in the various parameters (radial distribution of satellites, velocity anisotropy, external field effect), prevents to disentangle the models, which all can give pretty good fits to the data. In all cases, realistic radial variations of velocity anisotropy are used for the satellites, and a constant stellar-mass to light ratio for the host galaxies.
A long XMM-Newton observation of the mini-BAL QSO PG 1126-041 allowed us to detect a highly ionized phase of X-ray absorbing gas outflowing at v~15000 km/s. Physical implications are briefly discussed.
IGR J01583+6713 is a new transient source discovered by the INTEGRAL/IBIS hard X-ray surveys. Optical observations suggested that it should be a high mass X-ray binary, but its nature is still unclear. We used the INTEGRAL/IBIS data to study the nature of the transient hard X-ray source IGR J01583+6713 during its outburst. Temporal profiles and spectral properties of IGR J01583+6713 around its outburst on 2005 Dec 6 were obtained. During the outburst, the mean X-ray luminosity reached around 4\times 10^{35} erg s^{-1} in the energy range of 20 -- 100 keV. The continuum spectrum can be fitted by a bremsstrahlung model of kT\sim 45 keV or a power-law model of \Gamma\sim 2.1, and the electron resonant cyclotron absorption lines at \sim 35 keV and possible at \sim 63 keV were detected, suggesting that a magnetic neutron star of B\sim 4\times 10^{12} G is located in IGR J01583+6713. Timing analysis of the outburst light curve found a pulsation period of \sim 5.47 hr. Then we identify IGR J01583+6713 as a transient slow-pulsation X-ray pulsar with a magnetic neutron star. After the outburst, the flux of IGR J01583+6713 was decreasing and it could not be detected by IBIS after 2005 Dec 10. This property of a highly magnetized neutron star with a long pulsation period suggested that the transient X-ray pulsar IGR J01583+6713 could be a wind-fed accretion system.
We present a spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy NGC 4636 in the Virgo cluster. We selected target GC candidates using the Washington photometry derived from the deep CCD images taken at the KPNO 4m. Then we obtained the spectra of 164 target objects in the field of NGC 4636 using the Multi-Object Spectroscopy (MOS) mode of Faint Object Camera and Spectrograph (FOCAS) on the SUBARU 8.2m Telescope. We have measured the velocities for 122 objects: 105 GCs in NGC 4636, the nucleus of NGC 4636, 11 foreground stars, 2 background galaxies, and 3 probable intracluster GCs in the Virgo cluster. The GCs in NGC 4636 are located in the projected galactocentric radius within 10arcmin (corresponding to 43 kpc). The measured velocities for the GCs range from 300km/s to 1600km/s, with a mean value of 932_{-22}^{+25} km/s, which is in good agreement with the velocity for the nucleus of NGC 4636, 928\pm 45 km/s. The velocity dispersion of the GCs in NGC 4636 is derived to be 231_{-17}^{+15} km/s and the velocity dispersion of the blue GCs is slightly larger than that of the red GCs. Combining our results with data in the literature, we produce a master catalog of radial velocities for 238 GCs in NGC 4636. The velocity dispersion of the GCs in the master catalog is found to be 225_{-9}^{+12} km/s for the entire sample, 251_{-12}^{+18} km/s for 108 blue GCs, and 205_{-13}^{+11} km/s for 130 red GCs.
The solar transition region (TR), in which above the photosphere the tempera- ture increases rapidly and the density drops dramatically, is believed to play an important role in coronal heating and solar wind acceleration. Long-lasting up-flows are present in the upper TR and interpreted as signatures of mass supply to large coronal loops in the quiet Sun. Coronal bright points (BPs) are local heating phenomena and we found a different Doppler-shift pattern at TR and coronal temperatures in one BP, which might be related to the twisted loop system. The dominant energy loss in the lower TR is the Ly-alpha emission. It has been found that most Ly-alpha radiance profiles are stronger in the blue peak, an asymmetry opposite to higher order Lyman lines. This asymmetry is stronger when the downflow in the middle TR is stronger, indicating that the TR flows play an important role in the line formation process. The peak separation of Ly-alpha is found to be larger in coronal holes than in the quiet Sun, reflecting the different magnetic structures and radiation fields between the two regions. The Lyman line profiles are found to be not reversed in sunspot plume and umbra regions, while they are obviously reversed in the surrounding plage region. At TR temperatures, the densities of the sunspot plume and umbra are a factor of 10 lower than of the plage, indicating that the sunspot plasma emitting at TR temperatures is higher and possibly more extended above sunspots than above the plage region.
We present {\it Spitzer} IRAC mid-infrared photometry on the massive star forming region AFGL 437 (IRAS 03035+5819). From the IRAC colour-colour diagram, we identify several new embedded YSOs within 90 arcsec of the central compact cluster. Using the IRAC ratio images, we investigate the molecular outflows associated with the highly embedded young stellar object WK34 in the central cluster. We attribute the lobes seen (extended to $\sim$ 0.22 pc in the north) in the ratio map to shocked molecular hydrogen emission. IRAC images reveal a large diffuse nebulosity associated with the central cluster and extending up to $\sim$ 11.29 pc from south-west to north-east direction with its brightness gradually increasing from 3.6 to 8.0 $\mu$m. A dense box-car-shaped nebula (more than 2.0 pc in size) situated to the south-west of the cluster shows molecular hydrogen emission that may have been caused by shock waves from the compact cluster sources. It seems that these sources are also responsible for the infrared-bright nebulosity. Using a 2D radiative transfer model, we derive from the spectral energy distributions, the mass, age and luminosity of all the YSOs identified within the central cluster. The SED modelling shows that the driving engine of the outflows, WK34, appears to be massive but very young and deeply embedded. The weighted mean values of the masses and ages of the 21 YSOs derived from the model are in the range 1-10 \msun and 10$^{4.1 - 6.4}$ yr respectively; while their luminosities are in the range of 10$^{0.47-3.48}$ L$_{\odot}$.
From a model-independent point of view, we address the possibility that quark clustering could occur in cold quark matter at realistic baryon densities because of the likely strong coupling between quarks in compact stars.
We analyze pulsar fluxes at 1400 MHz ($S_{1400}$) and distances ($d$) extracted from the Parkes Multibeam Survey. Under the assumption that distribution of pulsar luminosities is distance-independent, we find that either (a) pulsar fluxes diminish with distance according to a non-standard power law, due, we suggest, to the presence of a component with $S_{1400} \propto 1/d$, or (b) that there are very significant (i.e. order of magnitude) errors in the dispersion-measure method for estimating pulsar distances. The former conclusion (a) supports a model for pulsar emission that has also successfully explained the frequency spectrum of the Crab and 8 other pulsars over 16 orders of magnitude of frequency, whilst alternative (b) would necessitate a radical re-evaluation of both the dispersion-measure method and current ideas about the distribution of free electrons within our Galaxy.
Motivated by theoretical studies of gravitational clustering in the Universe, we compute propagators (response functions) in the adhesion model. This model, which is able to reproduce the skeleton of the cosmic web and includes nonlinear effects in both Eulerian and Lagrangian frameworks, also corresponds to the Burgers equation of hydrodynamics. Focusing on the one-dimensional case with power-law initial conditions, we obtain exact results for Eulerian and Lagrangian propagators. We find that Eulerian propagators can be expressed in terms of the one-point velocity probability distribution and show a strong decay at late times and high wavenumbers, interpreted as a "sweeping effect" but not a genuine damping of small-scale structures. By contrast, Lagrangian propagators can be written in terms of the shock mass function -- which would correspond to the halo mass function in cosmology -- and saturate to a constant value at late times. Moreover, they show a power-law dependence on scale or wavenumber which depends on the initial power-spectrum index and is directly related to the low-mass tail of the shock mass function. These results strongly suggest that Lagrangian propagators are much more sensitive probes of nonlinear structures in the underlying density field and of relaxation processes than their Eulerian counterparts.
We determine the average mass profile of galaxy clusters at two different redshifts and compare its evolution with cosmological model predictions. We use two samples of galaxy clusters spanning similar (evolutionary corrected) mass ranges at different redshifts. The sample of low-redshift (z ~ 0.0-0.1) clusters is extracted from the ESO Nearby Abell Cluster Survey (ENACS) catalog. The sample of high-redshift (z ~ 0.4-0.8) clusters is mostly made of clusters from the ESO Distant Cluster Survey (EDisCS). We determine the average mass-profiles for these two cluster samples by solving the Jeans equation for hydrostatic equilibrium, using galaxies as tracers. By using two cluster galaxy populations, characterized by the presence and, respectively, absence of emission-lines in their spectra ('ELGs' and 'nELGs' hereafter), we are able to partially break the mass-profile orbital-anisotropy degeneracy. We find that the mass-profiles of both the nearby and the distant clusters are reasonably well fitted by a Navarro, Frenk and White (NFW) model. The best-fit values of the NFW concentration parameter are as predicted by cosmological numerical simulations; cluster mass-density profiles become more concentrated with time. The evolution of the number-density profile of nELGs proceeds in the opposite sense, becoming less concentrated with time. In our analysis we also recover the orbital anisotropy of nELGs and ELGs . We find that in low-z clusters nELGs follow almost isotropic orbits and ELGs have more radially-elongated orbits. In high-z clusters both nELGs and ELGs follow radially-elongated orbits. We discuss these results in terms of the predicted secular mass growth of galaxy clusters and the transformation of ELGs into nELGs.
We present a new determination of the solar nitrogen abundance making use of 3D hydrodynamical modelling of the solar photosphere, which is more physically motivated than traditional static 1D models. We selected suitable atomic spectral lines, relying on equivalent width measurements already existing in the literature. For atmospheric modelling we used the co 5 bold 3D radiation hydrodynamics code. We investigated the influence of both deviations from local thermodynamic equilibrium (non-LTE effects) and photospheric inhomogeneities (granulation effects) on the resulting abundance. We also compared several atlases of solar flux and centre-disc intensity presently available. As a result of our analysis, the photospheric solar nitrogen abundance is A(N) = 7.86 +/- 0.12.
The largest galaxies acquire their mass early on, when the Universe is still youthful. Cold streams violently feed these young galaxies a vast amount of fresh gas, resulting in very efficient star formation. Using a well resolved hydrodynamical simulation of galaxy formation, we demonstrate that these mammoth galaxies are already in place a couple of billion years after the Big Bang. Contrary to local starforming galaxies, where dust re-emits a large part of the stellar ultraviolet (UV) light at infrared and sub-millimetre wavelengths, our self-consistent modelling of dust extinction predicts that a substantial fraction of UV photons should escape from primordial galaxies. Such a model allows us to compute reliably the number of high redshift objects as a function of luminosity, and yields galaxies whose UV luminosities closely match those measured in the deepest observational surveys available. This agreement is remarkably good considering our admittedly still simple modelling of the interstellar medium (ISM) physics. The luminosity functions (LF) of virtual UV luminous galaxies coincide with the existing data over the whole redshift range from 4 to 7, provided cosmological parameters are set to their currently favoured values. Despite their considerable emission at short wavelengths, we anticipate that the counterparts of the brightest UV galaxies will be detected by future sub-millimetre facilities like ALMA
High-energy emissions are good indicators of peculiar behaviours in stars. We have therefore obtained an XMM-Newton observation of HD155806 and 1RXSJ171502.4-333344, and derived their spectral properties for the first time. The X-ray spectrum of HD155806 appears soft, even slightly softer than usual for O-type stars (as shown by a comparison with the O9 star HD155889 in the same XMM field). It is well-fitted with a two-component thermal model with low temperatures (0.2 and 0.6 keV), and it shows no overluminosity (log[LX/Lbol]=-6.75). The high-resolution spectrum, though noisy, reveals a few broad, symmetric X-ray lines (FWHM ~ 2500 km/s). The X-ray emission is compatible with the wind-shock model and therefore appears unaffected by the putative dense equatorial regions at the origin of the Oe classification. 1RXSJ171502.4-333344 is a nearby flaring source of moderate X-ray luminosity (log[LX/Lbol]=-3), with a soft thermal spectrum composed of narrow lines and presenting a larger abundance of elements (e.g. Ne) with a high first ionization potential (FIP) compared to lower-FIP elements. All the evidence indicates a coronal origin for the X-ray emission, in agreement with the dMe classification of this source.
We describe an hierarchical, frequency-domain beamforming architecture for synthesising a sky beam from the wideband antenna feeds of digital aperture arrays. The development of densely-packed, all-digital aperture arrays is an important area of research required for the Square Kilometre Array (SKA) radio telescope. The design of real-time signal processing systems for digital aperture arrays is currently a central challenge in pathfinder projects worldwide. In particular, this work describes a specific implementation of the beamforming architecture to the 2-Polarisation All-Digital (2-PAD) aperture array demonstrator.
Determining radiation location observationally plays a very important role in testing the pulsar radiation models. One-photon pair production in the strong magnetic field, $\gamma-e^{+}e^{1}$, is one of the important physical processes in pulsar radiation mechanisms. Photons near pulsar surface with sufficient energy will be absorbed in the magnetosphere and the absorption optical depth for these GeV $\gamma$-ray photons is usually large. In this paper, we include the aberrational, rotational and general relativistic effects and calculate the $\gamma$-B optical depth for $\gamma$-ray photons. Then we use the derived optical depth to determine the radiation altitude lower bounds for photons with given energies. As a case study, we calculate the lower bounds of radiation altitudes of Crab pulsar for photons with energy from 5 GeV to 1 TeV.
We discuss different ways that neutron stars can generate gravitational waves, describe recent improvements in modelling the relevant scenarios in the context of improving detector sensitivity, and show how observations are beginning to test our understanding of fundamental physics. The main purpose of the discussion is to establish promising science goals for third-generation ground-based detectors, like the Einstein Telescope, and identify the various challenges that need to be met if we want to use gravitational-wave data to probe neutron star physics.
Using the Tibet-III air shower array, we search for TeV gamma-rays from 27 potential Galactic sources in the early list of bright sources obtained by the Fermi Large Area Telescope at energies above 100 MeV. Among them, we observe 7 sources instead of the expected 0.61 sources at a significance of 2 sigma or more excess. The chance probability from Poisson statistics would be estimated to be 3.8 x 10^-6. If the excess distribution observed by the Tibet-III array has a density gradient toward the Galactic plane, the expected number of sources may be enhanced in chance association. Then, the chance probability rises slightly, to 1.2 x 10^-5, based on a simple Monte Carlo simulation. These low chance probabilities clearly show that the Fermi bright Galactic sources have statistically significant correlations with TeV gamma-ray excesses. We also find that all 7 sources are associated with pulsars, and 6 of them are coincident with sources detected by the Milagro experiment at a significance of 3 sigma or more at the representative energy of 35 TeV. The significance maps observed by the Tibet-III air shower array around the Fermi sources, which are coincident with the Milagro >=3sigma sources, are consistent with the Milagro observations. This is the first result of the northern sky survey of the Fermi bright Galactic sources in the TeV region.
This note gives a correction to the standard analysis of the delay pattern in the radio signals from a pulsar in a binary system; the same coordinate frame should be used for the transmission of the signal as for the motion of the pulsar in the field of its companion.
If the equation of state of dark energy is anisotropic there will be additional quadrupole anisotropy in the cosmic microwave background induced by the time dependent anisotropic stress quantified in terms of $\Delta w$. Assuming that the entire amplitude of the observed quadrupole is due to this anisotropy, we conservatively impose a limit of $|\Delta w| < 2.1\times 10^{-4}$ for any value of $w\ge -1$ assuming that $\Omega_{\rm m}<0.5$. This is considerably tighter than that which comes from SNe. Stronger limits, upto a factor of 10, are possible for specific values of $\Omega_{\rm m}$ and $w$. Since we assume this component is uncorrelated with the stochastic component from inflation, we find that both the expectation value and the sample variance are increased. There no improvement in the likelihood of an anomalously low quadrupole as suggested by previous work on an elliptical universe.
The astrometry technique is an important tool for detecting and characterizing exoplanets of different type. In this review, the different projects which are either operating, in construction or in discussion are presented and their performance discussed in the framework of the Blue Dots study. We investigate the sensitivity of astrometry to different sources of noise and we show that astrometry is a key technique in the path of discovering and characterizing new types of planets including the very challenging category of Earth-like planets orbiting the habitable zone of solar-type stars.
With the elementary energy release events introduced in a previous paper (Liu & Fletcher 2009) we model the chromospheric evaporation in flaring loops. The thick-target hard X-ray (HXR) emission produced by electrons escaping from the acceleration region dominates the impulsive phase and the thin-target emission from the acceleration region dominates the low-energy thermal component in the gradual phase, as observed in early impulsive flares. Quantitative details depend on properties of the thermal background, which leads to variations in the correlation between HXR flux and spectral index. For lower temperature and/or higher density of the background electrons, the HXRs both rise and decay more quickly with a plateau near the peak. The plateau is less prominent at higher energies. Given the complexity of transport of mass, momentum, and energy along loops in the impulsive phase, we propose a strategy to apply this single-zone energy release and electron acceleration model to observations of flares associated with single loops so that the energy release, electron acceleration, and evaporation processes may be studied quantitatively.
The SIM Lite mission will undertake several planet surveys. One of them, the Deep Planet Survey, is designed to detect Earth-mass exoplanets in the habitable zones of nearby main sequence stars. A double blind study has been conducted to assess the capability of SIM to detect such small planets in a multi-planet system where several giant planets might be present. One of the tools which helped in deciding if the detected planets were actual was an orbit integrator using the publicly available HNBody code so that the orbit solutions could be analyzed in terms of temporal stability over many orbits. In this contribution, we describe the implementation of this integrator and analyze the different blind test solutions. We discuss also the usefulness of this method given that some planets might be not detected but still affect the overall stability of the system.
High resolution spectral models for simple stellar populations (SSP) developed in the past few years have become a standard ingredient in studies of stellar population of galaxies. As more such models become available, it becomes increasingly important to test them. In this and a companion paper, we test a suite of publicly available evolutionary synthesis models using integrated optical spectra in the blue-near-UV range of 27 well studied star clusters from the work of Leonardi & Rose (2003) spanning a wide range of ages and metallicities. Most (23) of the clusters are from the Magellanic clouds. This paper concentrates on methodological aspects of spectral fitting. The data are fitted with SSP spectral models from Vazdekis and collaborators, based on the MILES library. Best-fit and Bayesian estimates of age, metallicity and extinction are presented, and degeneracies between these parameters are mapped. We find that these models can match the observed spectra very well in most cases, with small formal uncertainties in t, Z and A_V. In some cases, the spectral fits indicate that the models lack a blue old population, probably associated with the horizontal branch. This methodology, which is mostly based on the publicly available code STARLIGHT, is extended to other sets of models in Paper II, where a comparison with properties derived from spatially resolved data (color-magnitude diagrams) is presented. The global aim of these two papers is to provide guidance to users of evolutionary synthesis models and empirical feedback to model makers.
High spectral resolution evolutionary synthesis models have become a routinely used ingredient in extragalactic work, and as such deserve thorough testing. Star clusters are ideal laboratories for such tests. This paper applies the spectral fitting methodology outlined in Paper I to a sample of clusters, mainly from the Magellanic Clouds and spanning a wide range in age and metallicity, fitting their integrated light spectra with a suite of modern evolutionary synthesis models for single stellar population. The combinations of model plus spectral library employed in this investigation are Galaxev/STELIB, Vazdekis/MILES, SED@/GRANADA, and Galaxev/MILES+GRANADA, which provide a representative sample of models currently available for spectral fitting work. A series of empirical tests are performed with these models, comparing the quality of the spectral fits and the values of age, metallicity and extinction obtained with each of them. A comparison is also made between the properties derived from these spectral fits and literature data on these nearby, well studied clusters. These comparisons are done with the general goal of providing useful feedback for model makers, as well as guidance to the users of such models. We find that new generation of models using the GRANADA and MILES libraries are superior to STELIB-based models both in terms of spectral fit quality and regarding the accuracy with which age and metallicity are retrieved. Accuracies of about 0.1 dex in age and 0.3 dex in metallicity can be achieved as long as the models are not extrapolated beyond their expected range of validity.
We present a study of the intermediate regime between ultra-relativistic and nonrelativistic flow for gamma-ray burst afterglows. The hydrodynamics of spherically symmetric blast waves is numerically calculated using the AMRVAC adaptive mesh refinement code. Spectra and light curves are calculated using a separate radiation code that, for the first time, links a parametrisation of the microphysics of shock acceleration, synchrotron self-absorption and electron cooling to a high-performance hydrodynamics simulation.
Does light trace the mass? The generic answer is: NO. We thus need to understand how this could bias the clustering statistics we infer from data using different tracers. A first step to understand this is to study how dark matter halos, which host galaxies, trace the dark matter distribution. In this paper we explore the biasing in the clustering statistics of halos in simulations. We do so by looking at the two and three point correlation functions at large scales, as well as at the variance and skewness of one of the big (intermediate) simulations run by the MICE consortium. We find that we can predict the large scale halo clustering to better than 10% precision using the local (non-linear) biasing model and peak-background split anstaz. We also test directly the local bias prescription T = f(delta) between the mass fluctuations, delta, and its trace, T. We find the local linear, b1, and quadratic, c2, biasing parameters by fitting the f(delta) scattered relation directly from the halo-mass measurements in the simulation. These biases are then compared with the corresponding biases inferred from clustering measurements and with the peak-background split prediction, from the measured mass function. Differences in the b1 and c2 estimates can be as large as 10%. The discrepancy between the values of b1 from clustering and from the scatter relation can be attributed in part to the next to leading order correction in the local bias expansion. Using the peak-background split prediction results in a 5-10% systematic (and similar statistical) errors in the halo mass estimation out of these bias measurements. Although this is a potential warning for dark energy experiments, these systematics effects can in principle be calibrated using simulations.
Long Suzaku X-ray observations of the active galaxy NGC 4051 from 2005 and 2008 are analysed, in an attempt to reach a self-consistent understanding of the spectral variability on long timescales and at high time resolution. Principal components analysis and a maximum likelihood method of power spectrum analysis are used. In common with other type I AGN, the spectral variability is dominated by a varying-normalisation power-law component together with a quasi-steady, hard-spectrum offset component that contains Fe K atomic features. NGC 4051 displays a strong excess over a power-law at energies above 20 keV, some fraction of which also appears to vary with the power-law continuum. The power spectrum has a shape consistent with previous determinations, but significant differences are found between the low and high flux states of the source, demonstrating that the power spectrum is non-stationary. Frequency-dependent time lags between the hard and soft bands of up to 970+/-225s are measured. The existence of the observed lags excludes the possibility that the hard spectral component originates as reflection from the inner accretion disk. We instead show that the frequency- and energy-dependent time lags may be explained as reverberation, caused by reflection from a thick shell of material with maximum lags of about 10,000s. If the reflecting material surrounds the AGN, it extends to a distance about 1.5x10^14 cm, 600 gravitational radii, from the illuminating source and the global covering factor is C(g) >~ 0.4, confirming suggestions that type I AGN have high covering factors of absorbing and reflecting material. Given the spectral and timing similarities with other type I AGN, we infer that this structure is common in the type I population. [abridged]
We consider the growth of cosmological perturbations in modified gravity models where a scalar field mediates a non-universal Yukawa force between different matter species. The growth of the density contrast is altered for scales below the Compton wave-length of the scalar field. As the universe expands, the Compton wave-length varies in time in such a way that scales which where outside the range of the scalar field force may feel it at a lower redshift. In this case, both the exponent $\gamma$ measuring the growth of Cold Dark Matter perturbations and the shift function representing the ratio of the two Newtonian potentials $\psi$ and $\phi$ may differ from their values in General Relativity at low redshift.
The Large Underground Xenon (LUX) dark matter search experiment is currently being deployed at the Homestake Laboratory in South Dakota. We will highlight the main elements of design which make the experiment a very strong competitor in the field of direct detection, as well as an easily scalable concept. We will also present its potential reach for supersymmetric dark matter detection, within various timeframes ranging from 1 year to 5 years or more.
The mathematical theory of gravitational lensing has revealed many generic and global properties. Beginning with multiple imaging, we review Morse-theoretic image counting formulas and lower bound results, and complex-algebraic upper bounds in the case of single and multiple lens planes. We discuss recent advances in the mathematics of stochastic lensing, discussing a general formula for the global expected number of minimum lensed images as well as asymptotic formulas for the probability densities of the microlensing random time delay functions, random lensing maps, and random shear, and an asymptotic expression for the global expected number of micro-minima. Multiple imaging in optical geometry and a spacetime setting are treated. We review global magnification relation results for model-dependent scenarios and cover recent developments on universal local magnification relations for higher order caustics.
For purposes of stellar population analysis, emission corrections for Balmer series indices on the Lick index system in Sloan Digital Sky Survey (SDSS) stacked quiescent galaxy spectra are derived, along with corrections for continuum shape and gross stellar content, as a function of the Mg $b$ Lick index strength. These corrections are obtained by comparing the observed Lick index measurements of the SDSS with new observed measurements of 13 Virgo Cluster galaxies, and checked with model grids. From the H$\alpha$ Mg $b$ diagram a linear correction for the observed measurement is constructed using best fit trend lines. Corrections for H$\beta$, H$\gamma$ and H$\delta$ are constructed using stellar population models to predict continuum shape changes as a function of Mg $b$ and Balmer series emission intensities typical of H{\sc II} regions. The corrections themselves are fairly secure, but the interpretation for H$\delta$ and H$\gamma$ indices is complicated by the fact that the H$\delta$ and H$\gamma$ indices are sensitive to elemental abundances other than hydrogen.
We study the backreaction on the mean field geometry due to a non-conformal quantum field in a Robertson-Walker background. In the regime of small mass and small deviation from conformal coupling, we compute perturbatively the expectation value of the stress tensor of the field for a variety of vacuum states, and use it to obtain explicitly the semiclassical gravity solutions for isotropic perturbations around de Sitter spacetime, which is found to be stable. Our results show clearly the crucial role of the non-local terms that appear in the effective action: they cancel the contribution from local terms proportional to the logarithm of the scale factor which would otherwise become dominant at late times and prevent the existence of a stable self-consistent de Sitter solution. Finally, the opposite regime of a strongly non-conformal field with a large mass is also considered.
The GammeV experiment has constrained the couplings of chameleon scalar fields to matter and photons. Here we present a detailed calculation of the chameleon afterglow rate underlying these constraints. The dependence of GammeV constraints on various assumptions in the calculation is studied. We discuss GammeV--CHASE, a second-generation GammeV experiment, which will improve upon GammeV in several major ways. Using our calculation of the chameleon afterglow rate, we forecast model-independent constraints achievable by GammeV--CHASE. We then apply these constraints to a variety of chameleon models, including quartic chameleons and chameleon dark energy models. The new experiment will be able to probe a large region of parameter space that is beyond the reach of current tests, such as fifth force searches, constraints on the dimming of distant astrophysical objects, and bounds on the variation of the fine structure constant.
We propose a model of asymmetric dark matter (DM) where the dark sector is an identical copy of both forces and matter of the standard model (SM) as in the mirror universe models discussed in literature. In addition to being connected by gravity, the SM and DM sectors are also connected at high temperature by a common set of heavy right-handed Majorana neutrinos via their Yukawa couplings to leptons and Higgs bosons. The lightest nucleon in the dark (mirror) sector is a candidate for dark matter. The out of equilibrium decay of right-handed neutrino produces equal lepton asymmetry in both sectors via resonant leptogenesis which then get converted to baryonic and dark baryonic matter. The dark baryon asymmetry due to higher dark nucleon masses leads to higher dark matter density compared to the familiar baryon density that is observed. The standard model neutrinos in this case acquire masses from the inverse seesaw mechanism. A kinetic mixing between the U(1) gauge fields of the two sectors is introduced to guarantee the success of Big-Bang Nucleosynthesis.
A simple theory of supersymmetric dark matter (DM) naturally linked to neutrino flavour physics is studied. The DM sector comprises a spectrum of mixed lhd-rhd sneutrino states where both the sneutrino flavour structure and mass splittings are determined by the associated neutrino masses and mixings. Prospects for indirect detection from solar capture are good due to a large sneutrino-nucleon cross-section afforded by the inelastic splitting (solar capture limits exclude an explanation of DAMA/LIBRA). We find parameter regions where all heavier states will have decayed, leaving only one flavour mixture of sneutrino as the candidate DM. Such regions have a unique `smoking gun' signature--sneutrino annihilation in the Sun produces a pair of neutrino mass eigenstates free from vacuum oscillations, with the potential for detection at neutrino telescopes through the observation of a hard spectrum of nu_mu and nu_tau (for a normal neutrino hierarchy). Next generation direct detection experiments can explore much of the parameter space through both elastic and inelastic scattering. We show in detail that the observed neutrino masses and mixings can arise as a consequence of supersymmetry breaking effects in the sneutrino DM sector, consistent with all experimental constraints.
Coincident detections of electromagnetic (EM) and gravitational wave (GW) signatures from coalescence events of supermassive black holes are the next observational grand challenge. Such detections will provide the means to study cosmological evolution and accretion processes associated with these gargantuan compact objects. More generally, the observations will enable testing general relativity in the strong, nonlinear regime and will provide independent cosmological measurements to high precision. Understanding the conditions under which coincidences of EM and GW signatures arise during supermassive black hole mergers is therefore of paramount importance. As an essential step towards this goal, we present results from the first fully general relativistic, hydrodynamical study of the late inspiral and merger of equal-mass, spinning supermassive black hole binaries in a gas cloud. We find that variable EM signatures correlated with GWs can arise in merging systems as a consequence of shocks and accretion combined with the effect of relativistic beaming. The most striking EM variability is observed for systems where spins are aligned with the orbital axis and where orbiting black holes form a stable set of density wakes, but all systems exhibit some characteristic signatures that can be utilized in searches for EM counterparts. In the case of the most massive binaries observable by the Laser Interferometer Space Antenna, calculated luminosities imply that they may be identified by EM searches to z = 1, while lower mass systems and binaries immersed in low density ambient gas can only be detected in the local universe.
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We present the angular correlation function measured from photometric samples comprising 1562800 LRGs. Three LRG samples were extracted from the SDSS imaging data, based on colour-cut selections at z 0.35, 0.55 and 0.7 as calibrated by the spectroscopic surveys, SDSS-LRG, 2SLAQ, and the AAOmega LRG survey. The intermediate scale correlation functions show significant deviations from a single power-law fit with a break at ~1Mpc. For r=1-20Mpc and at fixed luminosity, we see virtually no evolution of the clustering with redshift and the data is consistent with a simple high peaks biasing model where the comoving LRG space density is constant with z. At fixed z, the LRG clustering amplitude increases with luminosity in accordance with the simple high peaks model, with a typical LRG dark matter halo mass > 10^13 Msun. For r < 1Mpc, the clustering evolution is faster and consistent with a virialised clustering model. Again this result is consistent with a model where the space density is constant with redshift. At large scales, our highest S/N combined w(theta) result, in its raw form, shows an apparent peak in reasonable agreement with the acoustic peak detected by Eisenstein et al. However, this feature does not scale with depth in the expected manner. Furthermore, when corrections for possible systematics are taken into account the correlation function may not be consistent with as high amplitude a peak as claimed by Eisenstein et al. This conclusion is strongly supported by independent angular power-spectral analyses of similar LRG samples. The w(theta) shape may then still be consistent with what is expected from the linear structure growth of a scale-invariant spectrum of initial perturbations, perhaps including a lower amplitude acoustic peak.
In this paper, we compare the relative sensitivities of gamma-ray and neutrino observations to the dark matter annihilation cross section in leptophilic models such as have been designed to explain PAMELA data. We investigate whether the high energy neutrino telescope IceCube will be competitive with current and upcoming searches by gamma-ray telescopes, such as the Atmospheric Cerenkov Telescopes (ACTs) (HESS, VERITAS and MAGIC), or the Fermi Gamma Ray Space Telescope, in detecting or constraining dark matter particles annihilating in dwarf spheroidal galaxies. We find that after ten years of observation of the most promising nearby dwarfs, IceCube will have sensitivity comparable to the current sensitivity of gamma-ray telescopes only for very heavy (m_X > 7 TeV) or relatively light (m_X < 200 GeV) dark matter particles which annihilate primarily to mu+mu-. If dark matter particles annihilate primarily to tau+tau-, IceCube will have superior sensitivity only for dark matter particle masses below the 200 GeV threshold of current ACTs. If dark matter annihilations proceed directly to neutrino-antineutrino pairs a substantial fraction of the time, IceCube will be competitive with gamma-ray telescopes for a much wider range of dark matter masses.
We study the growth of massive galaxies from z=2 to the present using data from the NEWFIRM Medium Band Survey. The sample is selected at a constant number density of n=2x10^-4 Mpc^-3, so that galaxies at different epochs can be compared in a meaningful way. We show that the stellar mass of galaxies at this number density has increased by a factor of ~2 since z=2, following the relation log(M)=11.45-0.15z. In order to determine at what physical radii this mass growth occurred we construct very deep stacked rest-frame R-band images at redshifts z=0.6, 1.1, 1.6, and 2.0. These image stacks of typically 70-80 galaxies enable us to characterize the stellar distribution to surface brightness limits of ~28.5 mag/arcsec^2. We find that massive galaxies gradually built up their outer regions over the past 10 Gyr. The mass within a radius of r=5 kpc is nearly constant with redshift whereas the mass at 5-75 kpc has increased by a factor of ~4 since z=2. Parameterizing the surface brightness profiles we find that the effective radius and Sersic n parameter evolve as r_e~(1+z)^-1.3 and n~(1+z)^-1.0 respectively. The data demonstrate that massive galaxies have grown mostly inside-out, assembling their extended stellar halos around compact, dense cores with possibly exponential radial density distributions. Comparing the observed mass evolution to the average star formation rates of the galaxies we find that the growth is likely dominated by mergers, as in-situ star formation can only account for ~20% of the mass build-up from z=2 to z=0. The main uncertainties in this study are possible redshift-dependent systematic errors in the total stellar masses and the conversion from light-weighted to mass-weighted radial profiles.
A nearby star having a near-transit of a galaxy will cause a time-dependent weak lensing of the galaxy. Because the effect is small, we refer to this as weak microlensing. This could provide a useful method to weigh low-mass stars and brown dwarfs. We examine the feasibility of measuring masses in this way and we find that a star causes measurable weak microlensing in a galaxy even at 10 Einstein radii away. Of order one magnitude I < 25 galaxy comes close enough to one or other of the ~100 nearest stars per year.
A valuable amount of information is available in peculiar velocities of galaxies. Peculiar velocity surveys have recently allowed the discovery of potential problems with LCDM. Nonetheless, their direct observation through distance measurements remains a daunting task. Another way of considering the problem is to use orbit reconstruction methods assuming some mass-to-light assignment for galaxies. We give here two applications of this procedure for the study of large-scale bulk flows and the dynamics of voids in the Local Universe. We concentrate our study on the use of the Monge-Ampere-Kantorovitch reconstruction technique. Using peculiar velocities reconstructed from the 2MASS Galaxy Redshift Survey, and after comparison with the NGB-3k peculiar velocity catalog, we look in the details of these peculiar velocities. More particularly, we estimate the constraints that the peculiar velocities put on the cosmology. The information on dynamics that is included in reconstructed orbits of galaxies also allows us to have a much better prescription for defining and identifying voids in simulations and redshift catalogs. We present this new technique and how voids may give us additional constraints on cosmology with current and future surveys.
We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass subgiants (1.5 < M*/Msun < 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26 (+9,-8)%, which is significantly higher than the ~5-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} MJup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around intermediate-mass stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ~ M^{alpha}P^{beta} dlnM dlnP, the observed planet frequency, and the detection limits we derived. We find that the values of alpha and beta for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4 sigma level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~ 50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.
We analyse cosmological hydrodynamic simulations that include observationally-constrained prescriptions for galactic outflows. If these simulated winds accurately represent winds in the real Universe, then material previously ejected in winds provides the dominant source of gas infall for new star formation at redshifts z<1. This recycled wind accretion, or wind mode, provides a third physically distinct accretion channel in addition to the "hot" and "cold" modes emphasised in recent theoretical studies. Because of the interaction between outflows and gas in and around halos, the recycling timescale of wind material (t_rec) is shorter in higher-mass systems, which reside in denser gaseous environments. In these simulations, this differential recycling plays a central role in shaping the present-day galaxy stellar mass function (GSMF). If we remove all particles that were ever ejected in a wind, then the predicted GSMFs are much steeper than observed; galaxy masses are suppressed both by the direct removal of gas and by the hydrodynamic heating of their surroundings, which reduces subsequent infall. With wind recycling included, the simulation that incorporates our favoured momentum-driven wind scalings reproduces the observed GSMF for stellar masses 10^9 < M < 5x10^10 Msolar. At higher masses, wind recycling leads to excessive galaxy masses and excessive star formation rates relative to observations. In these massive systems, some quenching mechanism must suppress the re-accretion of gas ejected from star-forming galaxies. In short, as has long been anticipated, the form of the GSMF is governed by outflows; the unexpected twist here for our simulated winds is that it is not primarily the ejection of material but how the ejected material is re-accreted that governs the GSMF.
We present constraints on canonical single-field inflation derived from WMAP five year, ACBAR, QUAD, BICEP data combined with the halo power spectrum from SDSS LRG7. Models with a non-scale-invariant spectrum and a red tilt n_s < 1 are now preferred over the Harrison-Zel'dovich model (n_s = 1, tensor-to-scalar ratio r = 0) at high significance. Assuming no running of the spectral indices, we derive constraints on the parameters (n_s, r) and compare our results with the predictions of simple inflationary models. The marginalised credible intervals read n_s = 0.962^{+0.028}_{-0.026} and r < 0.17 (at 95% confidence level). Interestingly, the 68% c.l. contours favour mainly models with a convex potential in the observable region, but the quadratic potential model remains inside the 95% c.l. contours. We demonstrate that these results are robust to changes in the datasets considered and in the theoretical assumptions made. We then consider a non-vanishing running of the spectral indices by employing different methods, non-parametric but approximate, or parametric but exact. With our combination of CMB and LSS data, running models are preferred over power-law models only by a Delta chi^2 ~ 5.8, allowing inflationary stages producing a sizable negative running -0.063^{+0.061}_{-0.049} and larger tensor-scalar ratio r < 0.33 at the 95% c.l. This requires large values of the third derivative of the inflaton potential within the observable range. We derive bounds on this derivative under the assumption that the inflaton potential can be approximated as a third order polynomial within the observable range.
Using the published WMAP 5-year data, we first show how sensitive the WMAP power spectra are to the form of the WMAP beam. It is well known that the beam profile derived from observations of Jupiter is non-Gaussian and indeed extends, in the W band for example, well beyond its 12.'6 FWHM core out to more than 1 degree. This means that even though the core width corresponds to wavenumber l=1800, the form of the beam still significantly affects the WMAP results even at l=200 which is the scale of the first acoustic peak. The difference between the raw C_l and the de-beamed C_l is ~70% at the scale of the first peak rising to ~400% at the scale of the second. New estimates of the Q, V and W-band beam profiles are then presented, based on a stacking analysis of the WMAP5 radio source catalogue and the temperature map. The radio sources show a significantly broader beam profile on scales of 10'-30' than that found by the WMAP team whose beam analysis is based on measurements of Jupiter. Beyond these scales the beam profiles from the radio sources are too noisy to give useful information. Furthermore, we find evidence that fainter radio sources imply wider beam profiles than the brighter sources and also tentative evidence for a non-linear relation between WMAP and ATCA/IRAM 95 GHz source fluxes. We discuss whether the wide beam profiles could be caused either by radio source extension or clustering and find that neither explanation is likely. The reasons for the difference between the radio source and the Jupiter beam profiles are still unclear. If the radio source profiles were then used to define the WMAP beam, there could be a dramatic change in the amplitude and position of even the first acoustic peak. It is therefore important to identify the reasons for the differences between these two beam profile estimates.
Massive black holes are nowadays believed to reside in most local galaxies. Studies have also established a number of relations between the MBH mass and properties of the host galaxy such as bulge mass and velocity dispersion. These results suggest that central MBHs, while much less massive than the host (~0.1%), are linked to the evolution of galactic structure. When did it all start? In hierarchical cosmologies, a single big galaxy today can be traced back to the stage when it was split up in hundreds of smaller components. Did MBH seeds form with the same efficiency in small proto-galaxies, or did their formation had to await the buildup of substantial galaxies with deeper potential wells? I briefly review here some of the physical processes that are conducive to the evolution of the massive black hole population. I will discuss black hole formation processes for `seed' black holes that are likely to place at early cosmic epochs, and possible observational tests of these scenarios.
We present a simple, largely empirical but physically motivated model, which is designed to interpret consistently multi-wavelength observations from large samples of galaxies in terms of physical parameters, such as star formation rate, stellar mass and dust content. Our model is both simple and versatile enough to allow the derivation of statistical constraints on the star formation histories and dust contents of large samples of galaxies using a wide range of ultraviolet, optical and infrared observations. We illustrate this by deriving median-likelihood estimates of a set of physical parameters describing the stellar and dust contents of local star-forming galaxies from the Spitzer Infrared Nearby Galaxy Sample (SINGS) and from a newly-matched sample of SDSS galaxies observed with GALEX, 2MASS, and IRAS. The model reproduces well the observed spectral energy distributions of these galaxies across the entire wavelength range from the far-ultraviolet to the far-infrared. We find important correlations between the physical parameters of galaxies which are useful to investigate the star formation activity and dust properties of galaxies. Our model can be straightforwardly applied to interpret observed ultraviolet-to-infrared spectral energy distributions (SEDs) from any galaxy sample.
We discuss our current understanding of the interior structure and thermal evolution of giant planets. This includes the gas giants, such as Jupiter and Saturn, that are primarily composed of hydrogen and helium, as well as the "ice giants," such as Uranus and Neptune, which are primarily composed of elements heavier than H/He. The effect of different hydrogen equations of state (including new first-principles computations) on Jupiter's core mass and heavy element distribution is detailed. This variety of the hydrogen equations of state translate into an uncertainty in Jupiter's core mass of 18 M_Earth. For Uranus and Neptune we find deep envelope metallicities up to 0.95, perhaps indicating the existence of an eroded core, as also supported by their low luminosity. We discuss the results of simple cooling models of our solar system's planets, and show that more complex thermal evolution models may be necessary to understand their cooling history. We review how measurements of the masses and radii of the ~50 transiting extrasolar giant planets are changing our understanding of giant planets. In particular a fraction of these planets appear to be larger than can be accommodated by standard models of planetary contraction. We review the proposed explanations for the radii of these planets. We also discuss very young giant planets, which are being directly imaged with ground- and space-based telescopes.
Plausibly spacetime is "foamy" on small distance scales, due to quantum fluctuations. We elaborate on the proposal to detect spacetime foam by looking for seeing disks in the images of distant quasars and AGNs. This is a null test in the sense that the continued presence of unresolved "point" sources at the milli-arc second level in samples of distant compact sources puts severe constraints on theories of quantized spacetime foam at the Planckian level. We discuss the geometry of foamy spacetime, and the appropriate distance measure for calculating the expected angular broadening. We then deal with recent data and the constraints they put on spacetime foam models. Thus far, images of high-redshift quasars from the Hubble Ultra-Deep Field (UDF) provide the most stringent test of spacetime foam theories. While random walk models (alpha = 1/2) have already been ruled out, the holographic (alpha=2/3) model remains viable. Here alpha~1 parametrizes the different spacetime foam models according to which the fluctuation of a distance L is given by ~ L^(1 - alpha) l_P^alpha, with l_P being the Planck length. Indeed, we see a slight wavelength-dependent blurring in the UDF images selected for this study. Using existing data in the HST archive we find it is impossible to rule out the alpha=2/3 model, but exclude all models with alpha<0.65.
Double-peaked broad lines in Active Galactic Nuclei (AGNs) may indicate the existence of a supermassive black hole (SMBH) binary whose two broad line regions (BLRs) contribute together to the line profile. An alternative interpretation of the double-peaked broad line feature is a disk origin for the line emission. We calculate the expected broad line profiles for a SMBH binary with various separations, using simple BLR models. Under reasonable assumptions that both BLRs are illuminated by the two black holes (BHs) and that the ionizing flux at the BLR position is roughly constant, we confirm the emergence of double-peaked features and radial velocity drifts of the two peaks due to the binary orbital motion when the two BHs are close enough such that the light-of-sight orbital velocity difference is larger than the FWHM of individual broad components. However, when the two BHs are even closer such that the two BLRs are no longer distinct, the line profile becomes more complex and there are no coherent radial velocity drifts in the two peaks with time. We discuss the temporal variations of the broad line profile for binary SMBHs and highlight the different behaviors of reverberation mapping in the binary and disk emitter scenarios.
We discuss the origin of the optical variations in the Narrow line Seyfert 1 galaxy NGC 4051 and present the results of a cross-correlation study using X-ray and optical light curves spanning more than 12 years. The emission is highly variable in all wavebands, and the amplitude of the optical variations is found to be smaller than that of the X-rays, even after correcting for the contaminating host galaxy flux falling inside the photometric aperture. The optical power spectrum is best described by an unbroken power law model with slope $\alpha=1.4^{+0.6}_{-0.2}$ and displays lower variability power than the 2-10 keV X-rays on all time-scales probed. We find the light curves to be significantly correlated at an optical delay of $1.2^{+1.0}_{-0.3}$ days behind the X-rays. This time-scale is consistent with the light travel time to the optical emitting region of the accretion disc, suggesting that the optical variations are driven by X-ray reprocessing. We show, however, that a model whereby the optical variations arise from reprocessing by a flat accretion disc cannot account for all the optical variability. There is also a second significant peak in the cross-correlation function, at an optical delay of $39^{+2.7}_{-8.4}$ days. The lag is consistent with the dust sublimation radius in this source, suggesting that there is a measurable amount of optical flux coming from the dust torus. We discuss the origin of the additional optical flux in terms of reprocessing of X-rays and reflection of optical light by the dust.
NGC1275, the central galaxy in the Perseus cluster, is the host of gigantic hot bipolar bubbles inflated by AGN jets observed in the radio as Perseus A. It presents a spectacular $H{\alpha}$-emitting nebulosity surrounding NGC1275, with loops and filaments of gas extending to over 50 kpc. The origin of the filaments is still unknown, but probably correlates with the mechanism responsible for the giant buoyant bubbles. We present 2.5 and 3-dimensional MHD simulations of the central region of the cluster in which turbulent energy, possibly triggered by star formation and supernovae (SNe) explosions is introduced. The simulations reveal that the turbulence injected by massive stars could be responsible for the nearly isotropic distribution of filaments and loops that drag magnetic fields upward as indicated by recent observations. Weak shell-like shock fronts propagating into the ICM with velocities of 100-500 km/s are found, also resembling the observations. The isotropic outflow momentum of the turbulence slows the infall of the intracluster medium, thus limiting further starburst activity in NGC1275. As the turbulence is subsonic over most of the simulated volume, the turbulent kinetic energy is not efficiently converted into heat and additional heating is required to suppress the cooling flow at the core of the cluster. Simulations combining the MHD turbulence with the AGN outflow can reproduce the temperature radial profile observed around NGC1275. While the AGN mechanism is the main heating source, the supernovae are crucial to isotropize the energy distribution.
We use three-dimensional numerical simulations to study self-organization in supersonic turbulence in molecular clouds. Our numerical experiments describe decaying and driven turbulent flows with an isothermal equation of state, sonic Mach numbers from 2 to 10, and various degrees of magnetization. We focus on properties of the velocity field and, specifically, on the level of its potential (dilatational) component as a function of turbulent Mach number, magnetic field strength, and scale. We show how extreme choices of either purely solenoidal or purely potential forcing can reduce the extent of the inertial range in the context of periodic box models for molecular cloud turbulence. We suggest an optimized forcing to maximize the effective Reynolds number in numerical models.
We report the results of a search for an emission line from radiatively decaying dark matter in the Chandra X-ray Observatory spectrum of the ultra-faint dwarf spheroidal galaxy Willman 1. 99% confidence line flux upper limits over the 0.4-7 keV Chandra bandpass are derived and mapped to an allowed region in the sterile neutrino mass-mixing angle plane that is consistent with recent constraints from Suzaku X-ray Observatory and Chandra observations of the Ursa Minor and Draco dwarf spheroidals. A significant excess to the continuum, detected by fitting the particle-background-subtracted source spectrum, indicates the presence of a narrow emission feature with energy 2.51 +/- 0.07 (0.11) keV and flux [3.53 +/- 1.95 (2.77)] X 10^(-6) photons/cm^2/s at 68% (90%) confidence. Interpreting this as an emission line from sterile neutrino radiative decay, we derive the corresponding allowed range of sterile neutrino mass and mixing angle using two approaches. The first assumes that dark matter is solely composed of sterile neutrinos, and the second relaxes that requirement. The detection is consistent with the sterile neutrino mass of 5.0 +/- 0.2 keV and a mixing angle in a narrow range for which neutrino oscillations can produce all of the dark matter and for which sterile neutrino emission from the cooling neutron stars can explain pulsar kicks, thus bolstering both the statistical and physical significance of our measurement.
We report an optimal extraction methodology, for the reduction of multi-object fibre spectroscopy data, operating in the regime of tightly packed (and hence significantly overlapping) fibre profiles. The routine minimises crosstalk between adjacent fibres and statistically weights the extraction to reduce noise. As an example of the process we use simulations of the numerous modes of operation of the AAOmega fibre spectrograph and observational data from the SPIRAL Integral Field Unit at the Anglo-Australian Telescope.
CARMENES, Calar Alto high-Resolution search for M dwarfs with Exo-earths with a Near-infrared Echelle Spectrograph, is a study for a next-generation instrument for the 3.5m Calar Alto Telescope to be designed, built, integrated, and operated by a consortium of nine German and Spanish institutions. Our main objective is finding habitable exoplanets around M dwarfs, which will be achieved by radial velocity measurements on the m/s level in the near-infrared, where low-mass stars emit the bulk of their radiation.
We review the results from multi-dimensional, time-dependent simulations of gas dynamics in AGN. We will focus on two types of outflows powered by radiation emitted from the AGN central engine: (i) outflows driven from the innermost part of an accretion disk and (2) outflows driven from a large-scale inflow that is likely the main supplier of material to the central engine. We discuss the relevance of both types of outflows to the so-called AGN feedback problem. However, the AGN feedback should not be considered separately from the AGN physics. Therefore, we also discuss the issue whether the properties of the same outflows are consistent with the gas properties in broad- and narrow-line regions.
One of the important microlensing applications to stellar atmospheres is the study of spots on stellar surface provided by the high resolution of caustic-crossing binary-lens events. In this paper, we investigate the characteristics of spot-induced perturbations in microlensing light curves and explain the physical background of the characteristics. We explore the variation of the spot-induced perturbations depending on various parameters characterizing the spot and investigate how well these parameters can be retrieved from observations in high-cadence future lensing surveys. From this, we find that although it would not be easy to precisely constrain the shape and the surface brightness contrast, the size and location of the spot on the stellar surface can be fairly well constrained from the analysis of lensing light curves.
With an orbital period of about 3.078 days, the double-lined spectroscopic binary HD 48099 is, still now, the only short-period O+O system known in the Mon OB2 association. Even though an orbital solution has already been derived for this system, few information are available about the individual stars. We present, in this paper, the results of a long-term spectroscopic campaign. We derive a new orbital solution and apply a disentangling method to recover the mean spectrum of each star. To improve our knowledge concerning both components, we determine their spectral classifications and their projected rotational velocities. We also constrain the main stellar parameters of both stars by using the CMFGEN atmosphere code and provide the wind properties for the primary star through the study of IUE spectra. This investigation reveals that HD 48099 is an O5.5 V((f))+O9 V binary with M_1 sin^3 i = 0.70 M_{\sun} and M_2 sin^3 i = 0.39 M_{\sun}, implying a rather low orbital inclination. This result, combined with both a large effective temperature and log g, suggests that the primary star (v sini ~ 91 km s^-1) is actually a fast rotator with a strongly clumped wind and a nitrogen abundance of about 8 times the solar value.
The incidence of sub-galactic level substructures is an important quantity, as it is a generic prediction of high-resolution Cold Dark Matter (CDM) models which is susceptible to observational test. Confrontation of theory with observations is currently in an uncertain state. In particular, gravitational lens systems appear to show evidence for flux ratio anomalies, which are expected from CDM substructures although not necessarily in the same range of radius as observed. However, the current small samples of lenses suggest that the lens galaxies in these systems are unusually often accompanied by luminous galaxies. Here we investigate a large sample of unlensed elliptical galaxies from the COSMOS survey, and determine the fraction of objects with satellites, in excess of background counts, as a function of satellite brightness and separation from the primary object. We find that the incidence of luminous satellites within 20 kpc is typically a few tenths of one percent for satellites of a few tenths of the primary flux, comparable to what is observed for the wider but shallower SDSS survey. Although the environments of lenses in the SLACS survey are compatible with this observation, the CLASS radio survey lenses are significantly in excess of this.
We present polarization measurements at 8.4, 22, and 43 GHz made with the VLA of a complete sample of extragalactic sources stronger than 1 Jy in the 5-year WMAP catalogue and with declinations north of -34 degrees. The observations were motivated by the need to know the polarization properties of radio sources at frequencies of tens of GHz in order to subtract polarized foregrounds for future sensitive Cosmic Microwave Background (CMB) experiments. The total intensity and polarization measurements are generally consistent with comparable VLA calibration measurements for less-variable sources, and within a similar range to WMAP fluxes for unresolved sources. A further paper will present correlations between measured parameters and derive implications for CMB measurements.
We undertake another attempt towards seismic modelling of the most intensive studied main sequence pulsators of the early B spectral type, $\nu$ Eridani. Our analysis is extended by a requirement of fitting not only pulsational frequencies but also the complex amplitude of the bolometric flux variation, $f$, related to each mode frequency. This approach, called {\it complex asteroseismology}, provides a unique test of stellar parameters, atmospheres and opacities. In particular, the concordance of the empirical and theoretical values of $f$ we obtained for the high-order g mode opens a new gate in seismic studies of the main-sequence hybrid pulsators. The most intriguing and challenging result is that whereas an agreement of the theoretical and empirical values of $f$ for the radial mode can be achieved only with the OPAL data, a preference for the OP tables is derived from the analysis of the high-order gravity mode.
To investigate the transient nature of supersoft sources (SSSs) in M 31, we compared SSS candidates of the XMM-Newton Deep Survey, ROSAT PSPC surveys and the Chandra catalogues in the same field. We found 40 SSSs in the XMM-Newton observations. While 12 of the XMM-Newton sources were brighter than the limiting flux of the ROSAT PSPC survey, only two were detected with ROSAT ~10 yr earlier. Five correlate with recent optical novae which explains why they were not detected by ROSAT. The remaining 28 XMM-Newton SSSs have fluxes below the ROSAT detection threshold. Nevertheless we found one correlation with a ROSAT source, which had significantly larger fluxes than during the XMM-Newton observations. Ten of the XMM-Newton SSSs were detected by Chandra with <1-~6 yr between the observations. Five were also classified as SSSs by Chandra. Of the 30 ROSAT SSSs three were confirmed with XMM-Newton, while for 11 sources other classifications are suggested. Of the remaining 16 sources one correlates with an optical nova. Of the 42 Chandra very-soft sources five are classified as XMM-Newton SSSs, while for 22 we suggest other classifications. Of the remaining 15 sources, nine are classified as transient by Chandra, one of them correlates with an optical nova. These findings underlined the high variability of the sources of this class and the connection between SSSs and optical novae. Only three sources, were detected by all three missions as SSSs. Thus they are visible for more than a decade, despite their variability.
Lagrangian smoothed particle hydrodynamics (SPH) is a well-established approach to model fluids in astrophysical problems, thanks to its geometric flexibility and ability to automatically adjust the spatial resolution to the clumping of matter. However, a number of recent studies have emphasized inaccuracies of SPH in the treatment of fluid instabilities. The origin of these numerical problems can be traced back to spurious surface effects across contact discontinuities, and to SPH's inherent prevention of mixing at the particle level. We here investigate a new fluid particle model where the density estimate is carried out with the help of an auxiliary mesh constructed as the Voronoi tessellation of the simulation particles instead of an adaptive smoothing kernel. This Voronoi-based approach improves the ability of the scheme to represent sharp contact discontinuities. We show that this eliminates spurious surface tension effects present in SPH and that play a role in suppressing certain fluid instabilities. We find that the new `Voronoi Particle Hydrodynamics' described here produces better results than SPH especially in shocks and turbulent regimes of pure hydrodynamical simulations. We also discuss formulations of the artificial viscosity needed in this scheme and how judiciously chosen correction forces can be derived in order to maintain a high degree of particle order and hence a regular Voronoi mesh. This is especially helpful in simulating self-gravitating fluids with existing gravity solvers used for N-body simulations.
We compile position and inclination angles for tilted ring fits to the warped dusty and gaseous disk spanning radius 1.8 to 6500 pc from recent observations. For radii exterior to a kpc, tilted ring orientations lie on an arc on a polar inclination versus position angle plot, suggesting that precession following a merger can account for the ring morphology. Three kinks in the ring orientations are seen on the polar plot, the one at radius of about 1.3 kpc we suspect corresponds to the location where self-gravity in the disk affects the ring precession rate. Another at a radius of about 600 pc may be associated with a gap in the gas distribution. A third kink is seen at a radius of 100 pc. A constant inclination tilted disk precessing about the jet axis may describe the disk between 100 and 20 pc but not interior to this. A model with disk orientation matching the molecular circumnuclear disk at 100 pc that decays at smaller radii to an inner flat disk perpendicular to the jet may account for disk orientations within 100 pc. Neither model would account for the cusps or changes in disk orientation at 100 or 600 pc.
Based on a new version of the Hipparcos catalogue and an updated Geneva-Copenhagen survey of F and G dwarfs, we analyze the space velocity field of about 17000 single stars in the solar neighborhood. The main known clumps, streams, and branches (Pleiades, Hyades, Sirius, Coma Berenices, Hercules, Wolf 630-alpha Ceti, and Arcturus) have been identified using various approaches. The evolution of the space velocity field for F and G dwarfs has been traced as a function of the stellar age. We have managed to confirm the existence of the recently discovered KFR08 stream. We have found 19 Hipparcos stars, candidates for membership in the KFR08 stream, and obtained an isochrone age estimate for the stream, 13 Gyr. The mean stellar ages of the Wolf 630-alpha Ceti and Hercules streams are shown to be comparable, 4--6 Gyr. No significant differences in the metallicities of stars belonging to these streams have been found. This is an argument for the hypothesis that these streams owe their origin to a common mechanism.
Shortly after birth, open clusters start dissolving; gradually losing stars into the surrounding star field. The time scale for complete disintegration depends both on their initial membership and location within the Galaxy. Open clusters undergoing the terminal phase of cluster disruption or open cluster remnants (OCRs) are notoriously difficult to identify. From an observational point, a combination of low number statistics and minimal contrast against the general stellar field conspire to turn them into very challenging objects. To make the situation even worst, random samples of field stars often display features that may induce to classify them erroneously as extremely evolved open clusters. In this paper, we provide a detailed study of the stellar content and kinematics of NGC 6863, a compact group of a few stars located in Aquila and described by the POSS as a non existent cluster. Nonetheless, this object has been recently classified as OCR. The aim of the present work is to either confirm or disprove its OCR status by a detailed star-by-star analysis. The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC3 catalogue, and high resolution spectroscopy as well as results from extensive $N$-body calculations. Our results show that the four brightest stars commonly associated to NGC 6863 form an asterism, a group of non-physically associated stars projected together, leading to the conclusion that NGC 6863 is not a real open cluster.
The DAMA/LIBRA set-up (about 250 kg highly radiopure NaI(Tl) sensitive mass) is running at the Gran Sasso National Laboratory of the I.N.F.N.. The first DAMA/LIBRA results confirm the evidence for the presence of a Dark Matter particle component in the galactic halo, as pointed out by the former DAMA/NaI set-up; cumulatively the data support such evidence at 8.2 sigma C.L. and satisfy all the many peculiarities of the Dark Matter annual modulation signature. The main aspects and prospects of this model independent experimental approach will be outlined.
We consider the diffuse gamma ray data from FERMI first year observations and compare them to the gamma ray fluxes predicted by Dark Matter annihilation or decay (both from prompt emission and from Inverse Compton Scattering), for different observation regions of the sky and a range of Dark Matter masses, annihilation/decay channels and Dark Matter galactic profiles. We find that the data exclude large regions of the Dark Matter parameter space not constrained otherwise and discuss possible directions for future improvements. Also, we further constrain Dark Matter interpretations of the e+e- PAMELA/FERMI spectral anomalies, both for the annihilating and the decaying Dark Matter case: under very conservative assumptions, only models producing dominantly mu+mu- and assuming a cored Dark Matter galactic profile can fit the lepton data with masses around 2 TeV.
We discuss the rest-frame UV emission between 5< z < 7 from the MareNostrum High-z Universe, a SPH simulation done with more than 2 billion particles. Cosmological simulations of galaxy formation generally overpredict the UV restframe luminosity function at high redshift, both at the bright and faint ends. In this Letter we explore a dust attenuation model where a larger extinction is applied to star populations younger than a given age, mimicking the effect of a clumpy interstellar medium. We show that this scenario fits reasonably well both the UV luminosity functions and the UV-continuum slopes derived from observations. The model assumes a large obscuration for stars younger than 25 Myr from the gas clouds where they should be embedded at their formation time. We find that the optical depth in these clouds should be between 30 and 100 times larger than the mean optical depth for the homogeneous part of the interstellar medium. These values are one order of magnitude larger than those estimated in local galaxies. Therefore, we conclude that LambdaCDM predictions for the high-z UV emission can accommodate the current observations if we consider a dust extinction model based on the assumption of a clumpy environment at high redshift.
This paper is the second in a series in which we present intermediate-resolution spectra for a complete sample of 14 compact radio sources, taken with the aim of investigating the impact of the nuclear activity on the cirumnuclear interstellar medium (ISM) in the early stages of radio source evolution. In the first paper we presented the kinematic results from the line modelling and reported fast outflows in the circumnuclear gas. Here, we use the line fluxes to investigate the physical conditions and dominant ionisation mechanisms of the emission line gas. We find evidence for large electron densities and high reddening in the nuclear regions, particularly in the broader, blueshifted components. These results are consistent with the idea that the young, recently triggered radio sources still reside in dense and dusty cocoons deposited by the recent activity triggering event. In addition, we find that the quiescent nuclear and extended narrow components are consistent with AGN photoionisation. For the nuclear broader and shifted components the results are less clear. Whilst there are suggestions that the broader components may be closer to shock plus precursor models on the diagnostic diagrams (with high electron temperatures and densities), we are unable to unambiguously distinguish the dominant ionisation mechanism using the optical emission line ratios. This is surprising given the strong evidence for jet-cloud interactions (broad emission lines, large outflow velocities and strong radio-optical alignments), which favours the idea that the warm gas has been accelerated in shocks driven by the radio lobes expanding through a dense cocoon of gas deposited during the triggering event.
We have obtained metallicities of ~ 360 red giant stars distributed in 15 Small Magellanic Cloud (SMC) fields from near-infrared spectra covering the CaII triplet lines using the VLT + FORS2. The errors of the derived [Fe/H] values range from 0.09 to 0.35 dex per star, with a mean of 0.17 dex. The metallicity distribution of the whole sample shows a mean value of [Fe/H] = -1.00 +- 0.02, with a dispersion of 0.32 +- 0.01, in agreement with global mean [Fe/H] values found in previous studies. We find no evidence of a metallicity gradient in the SMC. In fact, on analysing the metallicity distribution of each field, we derived mean values of [Fe/H] = -0.99 +- 0.08 and [Fe/H] = -1.02 +- 0.07 for fields located closer and farther than 4 deg. from the center of the galaxy, respectively. In addition, there is a clear tendency for the field stars to be more metal-poor than the corresponding cluster they surround, independent of their positions in the galaxy and of the clusters' age. We argue that this most likely stems from the field stars being somewhat older and therefore somewhat more metal-poor than most of our clusters.
TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) is a monitoring program to study the parsec-scale structures and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Long Baseline Array and associated telescopes. Extragalactic jets south of -30 degrees declination are observed at 8.4 GHz and 22 GHz every two months at milliarcsecond resolution. The initial TANAMI sample is a hybrid radio and gamma-ray selected sample since the combination of VLBI and gamma-ray observations is crucial to understand the broadband emission characteristics of AGN.
The Galactic population of Open Clusters provides an insight into star formation in the Galaxy. The Open Cluster catalogue by Dias et al.(2002) provides a rich source of data, including kinematic information that enabled us to calculate the orbit of 481 Open Clusters. This large sample made it possible to carry out a systematic analysis of Open Cluster orbits, using parameters based on orbit eccentricity and separation from the Galactic plane. We show that these two parameters may be indicative of origin, and find them to be correlated. We also find them to be correlated with metallicity, another parameter suggested elsewhere to be a marker for origin. We also find that high values of any of these two parameters entail a low metallicity ([Fe/H]$<-$0.2). The resulting analysis points to four Open Clusters in the catalogue being of extra-Galactic origin by impact of High Velocity Cloud on the disk: Berkeley21, 32, 99, and Melotte66, with a further four being possibly due to this origin (NGC2158, 2420, 7789, IC1311). A further three may be due to Galactic Globular Cluster impact on the disk i.e of internal Galactic origin (NGC6791, 1817, and 7044).
We study the evolution of galaxy structure since z ~ 1 to the present. From a
GOODS-S multi-band catalog we define (blue) luminosity- and mass-weighted
samples, limited by M_B <= -20 and M_star >= 10^10 M_Sun, comprising 1122 and
987 galaxies, respectively. We extract early-type (E/S0/Sa) and late-type
(Sb-Irr) subsamples by their position in the concentration-asymmetry plane, in
which galaxies exhibit a clear bimodality.
We find that the early-type fraction, f_ET, rises with cosmic time, with a
corresponding decrease in the late-type fraction, f_LT, in both luminosity- and
mass-selected samples. However, the evolution of the comoving number density is
very different: the decrease in the total number density of M_B <= -20 galaxies
since z = 1 is due to the decrease in the late-type population, which accounts
for ~75% of the total star-formation rate in the range under study, while the
increase in the total number density of M_star >= 10^10 M_Sun galaxies in the
same redshift range is due to the evolution of early types. This suggests that
we need a structural transformation between late-type galaxies that form stars
actively and early-type galaxies in which the stellar mass is located.
Comparing the observed evolution with the gas-rich major merger rate in
GOODS-S, we infer that only ~20% of the new early-type galaxies with M_star >=
10^10 M_Sun appeared since z ~ 1 can be explained by this kind of mergers,
suggesting that minor mergers and secular processes may be the driving
mechanisms of the structural evolution of intermediate-mass (M_star ~ 4x10^10
M_Sun) galaxies since z ~ 1.
The origin of Earth oceans is controversial. Earth could have acquired its water either from hydrated silicates (wet Earth scenario) or from comets (dry Earth scenario). [HDO]/[H2O] ratios are used to discriminate between the scenarios. High [HDO]/[H2O] ratios are found in Earth oceans. These high ratios are often attributed to the release of deuterium enriched cometary water ice, which was formed at low gas and dust temperatures. Observations do not show high [HDO]/[H2O] in interstellar ices. We investigate the possible formation of high [HDO]/[H2O] ratios in dense (nH> 1E6 cm^{-3}) and warm gas (T=100-1000 K) by gas-phase photochemistry in the absence of grain surface chemistry. We derive analytical solutions, taking into account the major neutral-neutral reactions for gases at T>100 K. The chemical network is dominated by photodissociation and neutral-neutral reactions. Despite the high gas temperature, deuterium fractionation occurs because of the difference in activation energy between deuteration enrichment and the back reactions. The analytical solutions were confirmed by the time-dependent chemical results in a 1E-3 MSun disc around a typical TTauri star using the photochemical code ProDiMo. The ProDiMo code includes frequency-dependent 2D dust-continuum radiative transfer, detailed non-LTE gas heating and cooling, and hydrostatic calculation of the disc structure. Both analytical and time-dependent models predict high [HDO]/[H2O] ratios in the terrestrial planet forming region (< 3 AU) of circumstellar discs. Therefore the [HDO]/[H2O] ratio may not be an unique criterion to discriminate between the different origins of water on Earth.
The high accuracy and long time span of photoelectric observations allow them to be used for multifactor analyses and refining some of the "fine" photometric effects in the light curves of close binary systems. The results obtained can be subsequently interpreted in terms of the model of mass flow from the optical component of the close binary systems onto the accretion disk of the neutron star, which can explain satisfactorily the irregularities of the gaseous flow, the "hot spot", and the presence of splashes moving in individual Keplerian trajectories about the outer parts of the accretion disk of the neutron star Her X-1.
We invert directly the redshift - luminosity distribution of observed long Swift GRBs to obtain their rate and luminosity function. Our best fit rate is described by a broken power law that rises like (1+z)^2.1{+0.5 -0.6} for 0<z<3 and decrease like (1+z)^-1.4{+2.4-1.0} for z>3. This transition begins earlier and its amplitude is somewhat smaller than the corresponding transition in the SFR. The local rate is 1.3{+0.6 -0.7} [Gpc^-3 yr^-1]. The luminosity function is well described by a broken power law with a break at L* = 10^52.5+-0.2[erg/sec] and with indices alpha = 0.2{+0.2 -0.1} and beta = 1.4{+0.3 -0.6}. The recently detected GRB 090423, with redshift 8, fits nicely into the model's prediction, verifying that we are allowed to extend our results to high redshifts. For non evolving luminosity functions we can rule out a GRB rate that follows the star formation rate (SFR), unless the latter is steeply rising at large redshifts.
In previous work it was shown that MOND theories predict anomalously strong tidal stresses near the saddle points of the Newtonian gravitational potential. An analytical examination of the saddle between two bodies revealed a linear and a non-linear solution, valid for the outer and inner regions. Here we present a numerical algorithm for solving the MOND equations. We check the code against the two-body analytical solutions and explore the region transitioning between them. We then develop a a realistic model for the MONDian effects on the saddles of the Sun-Earth-Moon system (including further sources is straightforward). For the Sun-Earth saddle we find that the two-body results are almost unchanged, with corrections increasing from full to new Moon. In contrast, the Moon saddle is an intrinsically three-body problem, but we numerically find a recipe for adapting the two-body solution to this case, by means of a suitable re-scaling and axis re-orientation. We explore possible experimental scenarios for LISA Pathfinder, and the prospect of a visit to the saddle(s) at the end of the mission. Given the chaotic nature of the orbits, awareness of the full range of the possibilities is crucial for a realistic prediction. We conclude that even with very conservative assumptions on the impact parameter, the accelerometers are abundantly sensitive to vindicate or rule out the theory.
Taking into account the experimental results of the HiRes and AUGER collaborations, the present status of bounds on Lorentz symmetry violation (LSV) patterns is discussed. Although significant constraints will emerge, a wide range of models and values of parameters will still be left open. Cosmological implications of allowed LSV patterns are discussed focusing on the origin of our Universe, the cosmological constant, dark matter and dark energy. Superbradyons (superluminal preons) may be the actual constituents of vacuum and of standard particles, and form equally a cosmological sea leading to new forms of dark matter and dark energy.
Just comparing with the scenario that the (3+1)-dimensional "real world" of
the Calabi-Yau compactification has a tremendous landscape, we conjecture that
a (4+1)-dimensional holographic theory may also hold a landscape of its vacua.
Unlike the traditional studies of the AdS/CFT phenomenology where the vacua are
always constructive, we discuss the proper holographic vacua and their flux
compactification, starting from some general compact Einstein manifolds. The
proper vacua should be restricted by (i) a consistent worldsheet theory that
possesses the superconformal symmetry, (ii) some definite symmetries to
keep/break the corresponding symmetries of the dual field theory, (iii) certain
brane/flux configurations to cancel anomalies, and (iv) stabilities. We
consider diverse fundamental parameters of the dual field theory, fixed by some
special vacuum moduli.
In an opposite way, if some field theory such as QCD holds an AdS dual, it
may also possesses various fundamental parameters by an "landscape" of its
vacuum. Different vacua may be adjacent with each other, and divided by domain
walls. If the size of a single vacuum region is smaller than the visible
universe, it may be testable. We discuss the consequences of this conjecture in
the astrophysical environments, include but not limit to: (i) consistency with
the critical energy density of the universe, (ii) the behaviors of cosmic rays,
(iii) the stability and abundance of deuterons and other nuclei in the big-bang
nucleosynthesis and the star burning scenarios, and (iv) the existence of
strange/charm stars.
Several authors have recently argued that a satisfactory inflationary scenario can be implemented in the Standard Model (SM) by introducing a strong non-minimal coupling of the Higgs doublet to gravity. It is shown here that type I seesaw physics containing right handed neutrinos at intermediate scales can have a significant impact on the inflationary predictions of these models. For one such model, values of the scalar spectral index lower than the tree level prediction of 0.968 are realized for plausible values of the seesaw parameters and a SM Higgs boson mass close to 130 GeV. A precise measurement of n_s by PLANCK, as well as measurement of the Higgs boson mass by LHC should provide stringent tests of this SM based inflationary scenario supplemented by type I seesaw physics.
I present recent work on gravitational waves (GWs) from a generic Standard Model-like effective potential for the electroweak phase transition. We derive a semi-analytic expression for the approximate tunneling temperature, and analytic and approximate expressions for the two GW parameters $\alpha$ and $\beta$. A quick summary of our analysis and general results, as well as a list of some specific models which easily fit into this framework, are presented. The work presented here has been done in collaboration with Stefano Profumo (arXiv:0911.0687).
We systematically study spherically symmetric static spacetimes filled with a fluid in the Horava-Lifshitz theory of gravity with projectability, but without a detailed balance condition. We first show that all static solutions can be brought into a canonical Arnowitt-Deser-Misner form, which explicitly satisfies the projectability condition, if we momentarily restore the broken diffeomorphisms. Then we establish that when the spacetime is spatially Ricci flat the unique vacuum solution is the Schwarzshcild-de Sitter solution, while when the spacetime has a non-zero constant curvature, there exist two different vacuum solutions; one is an (Einstein) static universe, and the other is a new spacetime. This latter space is maximally symmetric, is not flat and free of spacetime singularities. We find all the perfect fluid solutions for such spacetimes, in addition to a class of anisotropic fluid solutions of the spatially Ricci flat spacetimes. All these solutions are free of a spacetime singularity at the center. To construct spacetimes that represent stars, we investigate junction conditions across the surfaces of stars and obtain the general matching conditions with or without the presence of infinitely thin shells. It is remarkable that, in contrast to General Relativity, the radial pressure of a star does not necessarily vanish on its surface even without the presence of a thin shell. Applying the junction conditions to our explicit solutions, we show that it is possible to match smoothly these solutions (all with non-zero radial pressures) to vacuum spacetimes without the presence of thin matter shells on the surfaces of stars.
We study the phenomenology of a realistic version of the chaotic inflationary model, which can be fully and directly explored in particle physics experiments. The inflaton mixes with the Standard Model Higgs boson via the scalar potential, and no additional scales above the electroweak scale are present in the model. The inflaton-to-Higgs coupling is responsible for both reheating in the Early Universe and the inflaton production in particle collisions. We find the allowed range of the light inflaton mass, 270 MeV <~ m_chi <~ 1.8 GeV, and discuss the ways to find the inflaton. The most promising are two-body kaon and B-meson decays with branching ratios of orders 10^{-9} and 10^{-6}, respectively. The inflaton is unstable with the lifetime 10^{-9}--10^{-10} s. The inflaton decays can be searched for in a beam-target experiment, where, depending on the inflaton mass, from several billions to several tenths of millions inflatons can be produced per year with modern high-intensity beams.
The topic of Lorentz invariance violation is a fundamental question in physics that has taken on particular interest in theoretical explorations of quantum gravity scenarios. I discuss various gamma-ray observations that give limits on predicted potential effects of Lorentz invariance violation. Among these are spectral data from ground based observations of the multi-TeV gamma-rays from nearby AGN, INTEGRAL detections of polarized soft gamma-rays from the vicinity of the Crab pulsar, Fermi Gamma Ray Space Telescope studies of photon propagation timing from gamma-ray bursts, and Auger data on the spectrum of ultrahigh energy cosmic rays. These results can be used to seriously constrain or rule out some models involving Planck scale physics. Possible implications of these limits for quantum gravity and Planck scale physics will be discussed.
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