In this letter we present a study of the size luminosity relation of 475 early-type galaxies in the Virgo Cluster with Sloan Digital Sky Survey imaging data. The analysis of our homogeneous, model-independent data set reveals that giant and dwarf early-type galaxies do not form one common sequence in this relation. The dwarfs seem to show weak or no dependence on luminosity, and do not fall on the extension of the rather steep relation of the giants. Under the assumption that the light profile shape varies continuously with magnitude, a curved relation of size and magnitude would be expected. While the galaxies do roughly follow this trend overall, we find that the dwarf galaxies are significantly larger and the low-luminosity giants are significantly smaller than what is predicted. We come to the conclusion that in this scaling relation there is not one common sequence from dwarfs to giants, but a dichotomy which can not be resolved by varying profile shapes. The comparison of our data to a semi-analytic model supports the idea of a physical origin of this dichotomy.
It has been claimed that Period-Luminosity relations derived from infrared observations of Large Magellanic Cloud (LMC) Cepheids are less dependent on the metallicity of the Cepheids. In this work, infrared observations of LMC Cepheids from the SAGE survey are combined with OGLE II optical observation to model and predict mass-loss rates. The mass-loss rates are fit to the data and are predicted to range from about 10^{-12} to 10^{-7}M_\odot/yr; however, the rates depend on the assumed value of the dust-to-gas ratio. By comparing the relations derived from observations to the relations derived from predicted infrared stellar luminosities from the mass-loss model, it is shown mass loss affects the structure and scatter of the infrared Period-Luminosity relation. Mass loss produces shallower slopes of the infrared relations and a lower zero point. There is also evidence for non-linearity in the predicted Period-Luminosity relations, and it is argued that mass loss produces larger infrared excess at lower periods, which affects the slope and zero point, making the PL relations more linear in the wavelength range of 3.6 to 5.8 micron. Because the dust-to-gas ratio is metallicity dependent and mass loss may have a metallicity dependence, infrared Period-Luminosity relations have additional uncertainty due to metallicity.
We show that, by studying the arrival times of radio pulses from highly-magnetized pulsars, it may be possible to detect light spin-0 bosons (such as axions and axion-like particles) with a much greater sensitivity, over a broad particle mass range than is currently reachable by terrestrial experiments and indirect astrophysical bounds. In particular, we study the effect of splitting of photon-boson beams under intense magnetic field gradients in magnetars and show that radio pulses (at meter wavelengths) may be split and shift by a discernible phase down to a photon-boson coupling constant of g ~ 1e-14 [1/GeV]; i.e., about four orders of magnitude lower than current upper limits on g. The effect increases linearly with photon wavelength with split pulses having equal fluxes and similar polarizations. These properties make the identification of beam-splitting and beam deflection effects straightforward with currently available data. Better understanding of radio emission from magnetars is, however, required to confidently exclude regions in the parameter space when such effects are not observed.
We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7 M_sun. We present here the first results from this project -- the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hbeta lag measurement in this object of 4.25(+0.68/-0.66) days in the observed frame. Coupled with the width of the Hbeta emission line in the variable spectrum, we determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hbeta emission line which clearly shows infalling gas in the Hbeta-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.
A quantitative theory of spectral lags for $\gamma$-ray bursts (GRBs) is given. The underlying hypothesis is that GRB subpulses are photons that are scattered into our line of sight by local concentrations of baryons that are accelerated by radiation pressure. For primary spectra that are power laws with exponential cutoffs, the width of the pulse and its fast rise, slow decay asymmetry is found to increase with decreasing photon energy, and the width near the exponential cutoff scales approximately as $E_{ph}^{-\eta}$, with $\eta\sim 0.4$, as observed. The spectral lag time is naturally inversely proportional to luminosity, all else being equal, also as observed.
When gauged cosmic strings form in a symmetry-breaking phase transition, the gauge field configuration at the time becomes imprinted in the spatial string distribution by the flux trapping mechanism. It is shown that quantum and thermal gauge field fluctuations give rise to long-range superhorizon correlations in the string network. Numerical simulations in the Abelian Higgs model confirm this finding. In contrast, the Kibble-Zurek mechanism, which most cosmic string studies are based on, only gives rise to short-distance subhorizon correlations. The potential observable effects of the correlations are discussed.
We examine the properties of galaxies in compact groups identified in a mock galaxy catalogue based upon the Millennium Run simulation. The overall properties of groups identified in projection are in general agreement with the best available observational constraints. However, only ~30% of these simulated groups are found to be truly compact in 3 dimensions, suggesting that interlopers strongly affect our observed understanding of the properties of galaxies in compact groups. These simulations predict that genuine compact group galaxies are an extremely homogeneous population, confined nearly exclusively to the red sequence: they are best described as `red and dead' ellipticals. When interlopers are included, the population becomes much more heterogeneous, due to bluer, star-forming, gas-rich, late-type galaxies incorrectly identified as compact group members. These models suggest that selection of members by redshift, such that the line-of-sight velocity dispersion of the group is less than 1000 km/s, significantly reduces contamination to the 30% level. Selection of members by galaxy colour, a technique used frequently for galaxy clusters, is also predicted to dramatically reduce contamination rates for compact group studies.
We propose a new method to search for light (pseudo-)scalar particles in the spectra of compact astrophysical objects such as magnetars, pulsars, and quasars. On accounts of compact astrophysical objects having intense magnetic fields extending over large volumes, they provide good conditions for efficient photon-particle oscillations via the Primakoff process. In particular, we show that if the coupling constant for light (<1e-2 eV) axions, g>1e-13 [1/GeV] then it is likely that absorption-like features would be detectable in the spectrum of compact astrophysical sources.
It is noted that X-ray tails (XRTs) of short, hard $\gamma$-ray bursts (SHBs) are similar to X-ray flashes (XRFs). We suggest a universal central engine hypothesis, as a way of accounting for this curiosity, in which SHBs differ from long $\gamma$-ray bursts (GRBs) in prompt emission because of the differences in the host star and attendant differences in the environment they present to the compact central engine (as opposed to differences in the central engine itself). Observational constraints and implications are discussed, especially for confirming putative detections of gravitational waves from merging compact objects.
We present the global distribution of fine structure infrared line emission in the Cassiopeia A supernova remnant using data from the Spitzer Space Telescope's Infrared Spectrograph. We identify emission from ejecta materials in the interior, prior to their encounter with the reverse shock, as well as from the post-shock bright ring. The global electron density increases by >~100 at the shock to ~10^4 cm^-3, providing evidence for strong radiative cooling. There is also a dramatic change in ionization state at the shock, with the fading of emission from low ionization interior species like [SiII], giving way to [SIV] and, at even further distances, high-energy X-rays from hydrogenic silicon. Two compact, crescent-shaped clumps with highly enhanced neon abundance are arranged symmetrically around the central neutron star. These neon crescents are very closely aligned with the "kick" direction of the compact object from the remnant's expansion center, tracing a new axis of explosion asymmetry. They indicate that much of the apparent macroscopic elemental mixing may arise from different compositional layers of ejecta now passing through the reverse shock along different directions.
The motivation and the current status of top-down models as sources of ultrahigh energy cosmic rays (UHECR) are reviewed. Stimulated by the AGASA excess, they were proposed as the main source of UHECRs beyond the GZK cutoff. Meanwhile searches for their signatures have limited their contribution to the UHECR flux to be subdominant, while the theoretical motivation for these searches remained strong: Topological defects are a generic consequence of Grand Unified Theories and superheavy particles are a creditable dark matter candidate. While Fermi/GLAST results should help to improve soon bounds on topological defects from the diffuse gamma-ray background, the most promising detection method are UHE neutrino searches. Superheavy dark matter can be restricted or detected by its characteristic galactic anisotropy combined with searches for UHE photons.
In this article we review the theory of cosmological inflation with a particular focus on the beautiful connection it provides between the physics of the very small and observations of the very large. We explain how quantum mechanical fluctuations during the inflationary era become macroscopic density fluctuations which leave distinct imprints in the cosmic microwave background (CMB). We describe the physics of anisotropies in the CMB temperature and polarization and discuss how CMB observations can be used to probe the primordial universe.
This is the third of a series of papers in which the structure and kinematics
of disk galaxies is studied. Employing direct tilted-ring fits to the data cube
as introduced in Paper I, we perform an analysis of the "Spindle" galaxy NGC
2685, previously regarded as two-ringed polar ring galaxy.
Deep HI and optical (i'-band) observations are presented. The HI observations
strongly suggest that the gaseous structure of NGC 2685 does not consist of two
separate mutually inclined regions, but forms a coherent, extremely warped
disk, the appearance of two rings being due to projection effects. By comparing
the HI total-intensity maps with the optical image we demonstrate that at large
radii a faint stellar disk is well aligned with the outer HI disk. The shape of
the dust-lanes obscuring the NE part of the inner stellar body indicates that
also at smaller radii NGC 2685 possesses a disk containing gas, dust, and stars
in which the various constituents are aligned. At smaller radii, this disk is
kinematically decoupled from the central stellar body. Hence, in the region of
the bright, central stellar body, NGC 2685 appears to consist of two disks that
share a common centre, but have different orientation: a bright stellar
lenticular body apparently devoid of dust and gas, and a heavily warped
low-surface brightness disk containing stars, gas and dust. The
low-surface-brightness disk changes its orientation gradually and at large
radii assumes the orientation of the central stellar S0 disk. Since, according
to our analysis, the intrinsic orientation of the low-surface-brightness disk
changes through 70 degrees, the gaseous disk is coherent, and is at no radius
orientated perpendicularly with respect to the central stellar body, NGC 2685
is likely not a classical polar-ring galaxy.
We develop a simple semi-analytic model of the star formation rate (SFR) as a function of time. We estimate the SFR for a wide range of values of the cosmological constant, spatial curvature, and primordial density contrast. Our model can predict such parameters in the multiverse, if the underlying theory landscape and the cosmological measure are known.
We present a new efficient method for computing the non-linearity parameters of the higher order correlation functions of local type curvature perturbations in inflation models having a $\cal N$-component scalar field, focusing on the non-Gaussianity generated during the evolution on super-horizon scales. In contrast to the naive expectation that the number of operations necessary to compute the $n$-point functions is proportional to ${\cal N}^n$, it grows only linearly in ${\cal N}$ in our formalism. Hence, our formalism is particularly powerful for the inflation models composed of a multi-component scalar field. Explicit formulas obtained by applying our method are provided for $n=2,3,4$ and 5, which correspond to power-, bi-, tri- and {\it quad}-spectra, respectively. We also discuss how many parameters we need to parameterize the amplitude and the shape of the higher order correlation functions of local type.
The results of a study of the AGB phase of stellar evolution are presented. Abundances have been determined for Fe, C, O, the light s-process elements, Y and Zr, the heavy s-process elements, La and Nd, and the r-process element, Eu. The expected relationship between enhanced C, increasing C/O ratio and enhanced s-process elements has been quantified. Results are presented to provide observational data with which to compare theoretical predictions. The results in this paper confirm previously suggested relationships between C, C/O and s-process element enhancements. It is seen that AGB stars show C/O ratios from C/O around 0.4 to 1.0, while C enhancements lie between [C/Fe]=0.1 to 0.9 dex. Enhancements of s-process elements are as much as [s/Fe] around 1.0 dex for the stars in which C is also greatly enhanced.
We conducted a target of opportunity X-ray observation of the classical nova V458 Vulpeculae 88 days after the explosion using the Suzaku satellite. With a 20 ks exposure, the X-ray Imaging Spectrometer detected X-ray emission significantly harder than typical super-soft source emission. The X-ray spectrum shows K lines from N, Ne, Mg, Si, and S, and L-series emission from Fe in highly ionized states. The spectrum can be described by a single temperature (0.64 keV) thin thermal plasma model in collisional equilibrium with a hydrogen-equivalent extinction column density of ~3e21/cm2, a flux of ~1e-12 erg/s/cm2, and a luminosity of ~6e34 erg/s in the 0.3-3.0 keV band at an assumed distance of 13 kpc. We found a hint of an enhancement of N and deficiencies of O and Fe relative to other metals. The observed X-ray properties can be interpreted as the emission arising from shocks of ejecta from an ONe-type nova.
We present the serendipitous discovery of z=4.05 molecular gas CO emission lines with the IRAM Plateau de Bure interferometer coincident with GN20 and GN20.2, two luminous submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North field (GOODS-N). These are currently the most distant submillimeter-selected galaxies reliably identified through CO emission and also some of the most luminous known. In terms of CO to bolometric luminosities, stellar mass and star formation rates (SFRs), these newly discovered z>4 SMGs are similar to z~1.5-3 SMGs studied to date. These z~4 SMGs have much higher specific SFRs than typical B-band dropout Lyman break galaxies at the same redshift. The stellar mass-SFR correlation for normal galaxies does not seem to evolve much further, between z~2 and z~4. A significant z=4.05 spectroscopic redshift spike is observed in GOODS-N, and a strong spatial overdensity of B-band dropouts and IRAC selected z>3.5 galaxies appears to be centered on the GN20 and GN20.2 galaxies. This suggests a proto-cluster structure with total mass ~10^14 Msun. Using photometry at mid-IR, submm and radio wavelengths, we show that reliable photometric redshifts (Dz/(1+z)~0.1) can be derived for SMGs over 1<z<4. This new photometric redshift technique has been used to provide a first estimate of the space density of 3.5<z<6 hyper-luminous starburst galaxies, and to show that they contribute substantially to the SFR density at early epochs. Many of these high-redshift starbursts will be within reach of Herschel. We find that the radio to mid-IR flux density ratio can be used to select z>3.5 starbursts, regardless of their submm/mm emission [abridged].
Hydrous silicates occur in various cosmic environments, and are among the minerals with the most pronounced bands in the far infrared (FIR) spectral region. Given that Herschel and ALMA will open up new possibilities for astronomical FIR and sub-mm spectroscopy, data characterizing the dielectric properties of these materials at long wavelengths are desirable. We aimed at examining the FIR spectra of talc, picrolite, montmorillonite, and chamosite, which belong to four different groups of phyllosilicates. We tabulated positions and band widths of the FIR bands of these minerals depending on the dust temperature. By means of powder transmission spectroscopy, spectra of the examined materials were measured in the wavelength range 25-500 mum at temperatures of 300, 200, 100, and 10 K. Room-temperature measurements yield the following results. For talc, a previously unknown band, centered at 98.5 mum, was found, in addition to bands at 56.5 and 59.5 mum. For montmorillonite, several bands at wavelengths <110 mum were detected, including a band at 105 mum with an FWHM of about 10 mum. Picrolite shows a sharp 77 mum FIR band. Chamosite is characterized by bands in the 72-92 mum range, and a prominent band at 277 mum. At decreasing temperature, most of the bands shift to shorter wavelengths. Examining a potential counterpart of the 105mum band in the spectra of HD 142527 and HD 100546, we find that the broad band in the spectra of these young stars - extending from 85 to 125 mum - cannot be due to montmorillonite or any of the hydrous silicates we studied, since these materials have sharper bands in the FIR wavelength range than previously assumed, especially at low temperatures.
Aims. We investigate the evolution of large- and small-scale magnetic fields in galaxies at high redshifts during the time of galaxy evolution. Methods. We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Turbulence in protogalactic halos generated by thermal virialization can drive an efficient turbulent dynamo. Results from simulations of hierarchical structure formation cosmology provide a tool to develop an evolutionary model of regular magnetic fields coupled to galaxy formation and evolution. Results. The turbulent (small-scale) dynamo was able to amplify a weak seed magnetic field in halos of protogalaxies to a few microG strength within a few 10^8 yr. This turbulent field served as a seed for the mean-field (large-scale) dynamo. Galaxies similar to the Milky Way formed their disks at z~4 and regular fields of microG strength and a few kpc coherence length were generated within 2 Gyr (at z~3), but field ordering up to the coherence scale of the galaxy size took another 6 Gyr (at z~0.5). Giant galaxies formed their disk already at z~10, allowing more efficient dynamo generation of strong regular fields (with kpc coherence length) already at z~4. However, the age of the Universe is short to achieve fully coherent fields in giant galaxies larger than 15 kpc. Dwarf galaxies should have hosted fully coherent fields already at ~1. After a major merger the strength of the turbulent field is enhanced by a factor of a few. Conclusions. This evolutionary scenario can be tested by measurements of polarized synchrotron emission and Faraday rotation with the planned Square Kilometre Array (SKA). We predict an anticorrelation between galaxy size and coherence scale (abridged).
The NEMO prototype detector, called "NEMO Phase-1", has been successfully operated at 2000 m depth from December 2006 to May 2007. The apparatus comprises a \emph{Junction Box} and a \emph{Mini-Tower} hosting 16 optical sensors. Preliminary results are presented. Positions of the optical sensors in the Mini-Tower were reconstructed through the acoustic positioning system with high level accuracy. Environmental parameters were analyzed. From data corresponding to a livetime of 11.3 hours, atmospheric muon tracks have been reconstructed and their angular distributions were measured and compared with Monte Carlo simulations.
We examine the internal dynamics and caustic structure of the rich cluster A1689, combining VLT/VIMOS spectroscopy with Subaru/Suprime-Cam imaging. The radial velocity distribution of $\sim 500$ cluster members is bounded by a pair of clearly defined velocity caustics, with a maximum amplitude of $\sim|4000|$ km/s at $\simeq$ 300 h$^{-1}$ kpc, beyond which the amplitude steadily declines, meeting at zero velocity at a limiting radius of $\simeq$ 2.1 h$^{-1}$ Mpc. We derive a 3D velocity anisotropy using a model-independent method to solve the Jeans equation,simultaneously incorporating the observed velocity dispersion profile, the galaxy counts from deep Subaru imaging, and our previously derived mass profile from a joint lensing/X-ray analysis. The velocity anisotropy is found to be predominantly radial at large radius and becomes increasing tangential towards the center, in agreement with physical expectations. We also solve the Jeans equation by assuming an NFW form for the mass distribution, finding a high concentration, $c_{vir}>9.75$, which is consistent with our joint lensing and X-ray estimate, $c_{vir}=12.2_{-1}^{+0.9}$. The caustic amplitude provides an independent mass profile via the escape velocity, after applying a small velocity anisotropy based correction. This mass profile is also in very good agreement with our earlier work and with the Jeans based dynamical analysis. The virial mass derived by both these dynamical methods is also in good agreement with our earlier lensing/X-ray analysis, providing an accurate combined constraint, $1.5<M_{vir}/(10^{15} h^{-1} M_{\odot})<1.65$. The inferred virial radius coincides with the limiting radius where the caustics meet at zero velocity and where the counts of cluster members ends, implying infall is not significant.
In the neutron-rich internal shocks model for gamma-ray bursts (GRBs), the Lorentz factors (LFs) of ion shells are variable, and so are the LFs of accompanying neutron shells. For slow neutron shells with a typical LF of approximate tens, the typical $\beta$-decay radius is $\sim 10^{14}-10^{15}$ cm. As GRBs last long enough [$T_{90}>14(1+z)$ s], one earlier but slower ejected neutron shell will be swept successively by later ejected ion shells in the range $\sim10^{13}-10^{15}$ cm, where slow neutrons have decayed significantly. Part of the thermal energy released in the interaction will be given to the electrons. These accelerated electrons will be mainly cooled by the prompt soft $\gamma-$rays and give rise to GeV emission. This kind of GeV emission is particularly important for some very long GRBs and is detectable for the upcoming satellite {\it Gamma-Ray Large Area Space Telescope} (GLAST).
The possible contribution of primordial black holes (PBHs) to the dark matter in the Universe has been discussed in various ways, implying consequences for observational astronomy. In this paper, we investigate probabilities and possible observational signatures of hypothetical collisions of PBHs with main sequence stars, red giants, white dwarfs, and neutron stars in our Galaxy. This has previously been discussed to lead to an observable photon eruption due to the shock produced in the passage. We find that such collisions are either too rare to be observed if masses of PBHs are typically larger than about 1e20 g, or they produce too little power to be detected if the PBHs masses are smaller than about 1e20 g. Apart from signals from those interactions, the only methods to probe their existence are the observation of their evaporation of the PBHs at masses of m~1e15 g and micro-lensing at masses around >1e26 g. Thus, the mass region between 1e15 g < m < 1e25 g remains unexplored and leaves space for some contribution of PBHs to the dark matter.
We present the current status of the QUIJOTE (Q-U-I JOint TEnerife) CMB Experiment, a new instrument which will start operations early 2009 at Teide Observatory, with the aim of characterizing the polarization of the CMB and other processes of galactic and extragalactic emission in the frequency range 10-30 GHz and at large angular scales. QUIJOTE will be a valuable complement at low frequencies for the PLANCK mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r=0.05.
We have constructed an optical photometer with microsecond time resolution, which is currently being operated on one of the H.E.S.S. telescopes. H.E.S.S. is an array of four Cherenkov telescopes, each with a 107 m^2 mirror, located in the Khomas highland in Namibia. In its normal mode of operation H.E.S.S. observes Cherenkov light from air showers generated by very high energy gamma-rays in the upper atmosphere. Our detector consists of seven photomultipliers, one in the center to record the lightcurve from the target and six concentric photomultipliers as a veto system to reject disturbing signals e.g. from meteorites or lightning at the horizon. The data acquisition system has been designed to continuously record the signals with zero deadtime. The Crab pulsar has been observed to verify the performance of the instrument and the GPS timing system. Compact galactic targets were observed to search for flares on timescales of a few microseconds to ~ 100 milliseconds. The design and sensitivity of the instrument as well as the data analysis method are presented.
Concatenating data from the millimetre regime to the infrared, we have
performed spectral energy distribution modelling for 227 of the 405 millimetre
continuum sources of Hill et al. (2005) which are thought to contain young
massive stars in the earliest stages of their formation. Three main parameters
are extracted from the fits: temperature, mass and luminosity. The method
employed was Bayesian inference, which allows a statistically probable range of
suitable values for each parameter to be drawn for each individual protostellar
candidate. This is the first application of this method to massive star
formation.
The cumulative distribution plots of the SED modelled parameters in this work
indicate that collectively, the sources without methanol maser and/or radio
continuum associations (MM-only cores) display similar characteristics to those
of high mass star formation regions. Attributing significance to the marginal
distinctions between the MM-only cores and the high-mass star formation sample
we draw hypotheses regarding the nature of the MM-only cores, including the
possibility that the population itself is comprised of different types of
source, and discuss their role in the formation scenarios of massive star
formation. In addition, we discuss the usefulness and limitations of SED
modelling and its application to the field. From this work, it is clear that
within the valid parameter ranges, SEDs utilising current far-infrared data can
not be used to determine the evolution of massive protostars or massive young
stellar objects.
The timescale over which planets may form in the circumstellar disks of young stars is one of the main issues of current planetary formation models. We present here new constraints on planet formation timescales derived from the rotational evolution of exoplanet host stars.
A spectroscopic support survey of 103 objects observed by the MOST satellite is presented; 96 are variable stars with 83 of them being new MOST variable-star detections or stars with variability types verified and/or modified on the basis of the MOST data. Analysis of 241 medium-resolution spectra using the broadening-functions formalism yielded radial velocities, projected rotational velocities (for 31 targets for which it was possible) and spectral type estimates. Seven new spectroscopic binaries were discovered; orbital solutions are given for two of them (HD73709, and GSC 0814-0323). The visual binary HD46180 was found to be composed of two close binary stars (eclipsing and non-eclipsing one) very probably forming a physical quadruple system.
We present an analysis of the spatial distribution of various stellar populations within the Large Magellanic Cloud. We combine mid-infrared selected young stellar objects, optically selected samples with mean ages between ~9 and ~1000 Myr, and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC. For the analysis we use Fractured Minimum Spanning Trees, the statistical Q parameter, and the two-point correlation function. Restricting our analysis to young massive (OB) stars we confirm our results obtained for M33, namely that the luminosity function of the groups is well described by a power-law with index -2, and that there is no characteristic length-scale of star-forming regions. We find that stars in the LMC are born with a large amount of substructure, consistent with a 2D fractal distribution with dimension ~1.8 and evolve towards a uniform distribution on a timescale of ~175 Myr. This is comparable to the crossing time of the galaxy and we suggest that stellar structure, regardless of spatial scale, will be eliminated in a crossing time. This may explain the smooth distribution of stars in massive/dense young clusters in the Galaxy, while other, less massive, clusters still display large amounts of structure at similar ages. By comparing the stellar and star cluster distributions and evolving timescales, we show that infant mortality of clusters (or 'popping clusters') have a negligible influence on galactic structure. Finally, we quantify the influence of the elongation, differential extinction, and contamination of a population on the measured Q value.
Centimeter and meter sized solid particles in protoplanetary disks are trapped within long lived high pressure regions, creating opportunities for collapse into planetesimals and planetary embryos. We study the accumulations in the stable Lagrangian points of a giant planet, as well as in the Rossby vortices launched at the edges of the gap it carves. We employ the Pencil Code, tracing the solids with a large number of interacting Lagrangian particles, usually 100,000. For particles of 1 cm to 10 cm radii, gravitational collapse occurs in the Lagrangian points in less than 200 orbits. For 5 cm particles, a 2 Earth mass planet is formed. For 10 cm, the final maximum collapsed mass is around 3 Earth masses. The collapse of the 1 cm particles is indirect, following the timescale of depletion of gas from the tadpole orbits. In the edges of the gap vortices are excited, trapping preferentially particles of 30 cm radii. The rocky planet that is formed is as massive as 17 Earth masses, constituting a Super-Earth. By using multiple particle species, we find that gas drag modifies the streamlines in the tadpole region around the classical L4 and L5 points. As a result, particles of different radii have their stable points shifted to different locations. Collapse therefore takes longer and produces planets of lower mass. Three super-Earths are formed in the vortices, the most massive having 4.4 Earth masses. We conclude that A Jupiter mass planet can induce the formation of other planetary embryos in the outer edge of its gas gap. Trojan Earth mass planets are readily formed, and although not existing in the solar system, might be common in the exoplanetary zoo.
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Several recent studies have considered modifications to the standard weakly-interacting massive particle (WIMP) scenario in which the cross section (times relative velocity v) for pair annihilation is enhanced by a factor 1/v. Since v~10^{-3} in the Galactic halo, this may boost the annihilation rate into photons and/or electron-positron pairs enough to explain several puzzling Galactic radiation signals. Here we show that if the annihilation cross section scales as 1/v, then there is a burst of WIMP annihilation in the first dark-matter halos that form at redshifts z ~ 100-200. If the annihilation is to gamma rays in the energy range 100 keV - 300 GeV, or to electron-positron pairs in the energy range GeV - 2 TeV, then there remains a contribution to the diffuse extragalactic gamma-ray background today. Upper limits to this background provide constraints to the annihilation cross section. If the photon or electron-positron energies fall outside these energy ranges, then the radiation is absorbed by the intergalactic medium (IGM) and thus ionizes and heats the IGM. In this case, cosmic microwave background constraints to the ionization history also put limits on the annihilation cross section.
We explore the nature of systematic errors that can arise in measurement of black hole masses from single-epoch spectra of active galactic nuclei (AGNs) by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio, S/N), and blending of spectral features by comparing the precision and accuracy of single-epoch mass measurements to those of recent reverberation mapping studies. We calculate masses by characterizing the broad Hbeta emission line by both the full width at half maximum and the line dispersion and demonstrate the importance of removing narrow emission-line components and host starlight. We find that the reliability of line width measurements rapidly decreases for S/N lower than ~10 to 20 (per pixel) and that fitting the line profiles instead of direct measurement of the data does not mitigate this problem but can, in fact, introduce systematic errors. We also conclude that a full spectral decomposition to deblend the AGN and galaxy spectral features is unnecessary except to judge the contribution of the host galaxy to the luminosity and to deblend any emission lines that may inhibit accurate line width measurements. Finally, we present an error budget which summarizes the minimum observable uncertainties as well as the amount of additional scatter and/or systematic offset that can be expected from the individual sources of error investigated. In particular, we find that the minimum observable uncertainty in single-epoch mass estimates due to variability is <~ 0.1 dex for high S/N (>~ 20 per pixel) spectra.
Because structure in the Universe is built up through galaxy mergers and nearly all galaxies host a central supermassive black hole (SMBH), some galaxies should possess two SMBHs near their centers as the result of a recent merger. These SMBHs spiral to the center of the resultant merger-remnant galaxy, and one or both of the SMBHs may power active galactic nuclei (AGN). Using the DEEP2 Galaxy Redshift Survey we have examined 1881 early-type galaxies, of which 107 exhibit [O III] and Hbeta emission lines indicative of AGN activity. Of these, 37 AGN have [O III] emission-line redshifts significantly different from the redshifts of the host galaxies' stars, corresponding to velocity offsets of ~50 km/s to ~300 km/s. Two of these AGN exhibit double-peaked [O III] emission lines, while the remaining 35 AGN each exhibit a single set of velocity-offset [O III] emission lines. These AGN velocity offsets cannot be readily explained by outflows, but rather are most likely the result of recent galaxy mergers. Based on this interpretation we find that roughly half of early-type galaxies hosting AGN are also merger remnants, which implies that mergers may trigger AGN activity in early-type galaxies. Our result sets a hard lower limit of 2.0% on the fraction of early-type galaxies at redshifts 0.34 < z < 0.82 that have recently undergone mergers. We also find a merger rate of ~3 mergers/Gyr, which includes both minor and major mergers, for early-type galaxies at redshifts 0.34 < z < 0.82.
If damped Lyman alpha systems (DLAs) contain even modest amounts of dust, the
ultraviolet luminosity of the background quasar can be severely diminished.
When the spectrum is redshifted, this leads to a bias in optical surveys for
DLAs. Previous estimates of the magnitude of this effect are in some tension;
in particular, the distribution of DLAs in the column-density -- metallicity
plane has led to claims that we may be missing a considerable fraction of metal
rich, high column density DLAs, whereas radio surveys do not unveil a
substantial population of otherwise hidden systems. Motivated by this tension,
we perform a Bayesian parameter estimation analysis of a simple dust
obscuration model. We include radio and optical observations of DLAs in our
overall likelihood analysis and show that these do not, in fact, constitute
conflicting constraints.
Our model gives statistical limits on the biasing effects of dust, predicting
that only 7% of DLAs are missing from optical samples due to dust obscuration;
at 2 sigma confidence, this figure takes a maximum value of 17%. This contrasts
with recent claims that DLA incidence rates are underestimated by 30 -- 50%.
Optical measures of the mean metallicities of DLAs are found to underestimate
the true value by just 0.1 dex (or at most 0.4 dex, 2 sigma confidence limit),
in agreement with the radio survey results of Akerman et al. The quantity most
affected by dust biasing is the total cosmic density of metals in DLAs,
Omega_{Z,DLA}, which is underestimated in optical surveys by a factor of
approximately two.
(Abridged.)
We present line-strength measurements for 74 early-type galaxies in the core of the Coma cluster reaching down to velocity dispersions, sigma, of 30 km/s. The index-sigma relations for our sample, including galaxies with sigma<100 km/s (low-sigma), differ in shape depending on which index is used. We notice two types of relations for the metallic indices: one showing a break in the slope around ~100 km/s, and another group with strong linear relations between an index and log sigma. We find no connection between the behavior of index-sigma relations with either alpha- or Fe-peak elements. However, we find indications that the relations are tighter for indices which do not depend on the micro-turbulent velocities of stellar atmospheres. We confirm previous results that low-sigma galaxies including dE/dS0s are on average younger, less metal rich, and have lower [alpha/Fe] in comparison to E/S0s. Our data show that these trends derived for high-sigma galaxies extend down to dE/dS0s. This is a factor of ~2 lower in sigma than previously published work. We confirm that the observed anti-correlation between age and metallicity for high-sigma galaxies is consistent with the effects of correlated errors. Low-sigma galaxies also show a similar relation between age and metallicity as a result of correlated errors. However, they are offset from this relationship so that, on average, they are less metal rich and younger than their high-sigma counterparts.
We have defined a new H_\beta absorption index definition, H$_{\beta_o}$, which has been optimized as an age indicator for old and intermediate age stellar populations. Rather than using stellar spectra, we employed for this purpose a library of stellar population SEDs of different ages and metallicities at moderately high spectral resolution. H$_{\beta_o}$ provides us with improved abilities for lifting the age-metallicity degeneracy affecting the standard Hbeta Lick index definition. The new index, which has also been optimized against photon noise and velocity dispersion, is fully characterized with wavelength shift, spectrum shape, dust extinction and [alpha/Fe] abundance ratio effects. H_\beta requires spectra of similar qualites as those commonly used for measuring the standard Hbeta Lick index definition. Aiming at illustrating the use and capabilities of H$_{\beta_o}$ as an age indicator we apply it to Milky Way globular clusters and to a well selected sample of early-type galaxies covering a wide range in mass. The results shown here are particularly useful for applying this index and understand the involved uncertainties.
We present new red optical spectra of V592 Cas aimed at exploring the properties of the outflow of this system in a spectral region where the underlying white dwarf and the accretion disk do not contribute significantly to the observed absorption components of the H-alpha and HeI line profiles. We use the H-alpha emission line to study the wind, which appears as pronounced blueshifted P-Cygni absorption troughs whose low velocity end contaminates the blue side of the emission line profile. The wind appears to be episodic in nature, with multiple events reaching velocities of 5000km/sec in H-alpha. Similar (but weaker) wind signatures appear in the HeI5876AA line but are absent in HeI6678AA. Our data suggest that during wind episodes the wind is phase dependent and is visible for half the orbit of the system. Considering that V592 Cas is viewed almost face-on, the symmetry axis of the outflow can not be orthogonal to the disk and/or the outflow must have some other inherent asymmetry in outflow geometry. A possible origin of the wind is in a disk hotspot, either at the initial impact point of the accretion stream on the disk edge or as a result of disk overflow (similar to SW Sextantis stars). Simultaneous optical photometry during one night of our spectroscopic observations indicate that there is no clear relationship between the optical brightness variations and the strength of the outflow in this system.
VLT adaptive optics images of NGC 253 with resolutions down to 200 mas resolve the central 300 pc of this galaxy in ~ 37 infrared (IR) bright knots, a factor 3 larger than previously reported, and extended diffuse emission. The angular resolution, comparable to that of available VLA 2 cm maps, permits us a very accurate IR-radio registration. Eight radio sources are found to have an IR counterpart. The knots have H\alpha equivalent width of about 80 angstroms, sizes of FWHM ~ 3 pc, magnitudes in L-band of about 12 mag and relatively high extinction, Av ~ 7 mag. Their spectral energy distributions (SEDs) look very similar, characterised by a maximum at 20 micron and a gentle bump in the 1 - 2 micron range. These features can be well reproduced by considering an important contribution of very young stellar objects to the IR, efficiently heating their dust envelope. The evidence indicates that these are young massive clusters bursting from their dust cocoons. A median SED of the knots is provided, which may represents one of the most genuine templates of an extragalactic circumnuclear star forming region. The lack of any optical or IR counterpart for the previously identified radio core calls into question its supposed AGN nature. This source may instead represents a scaled up version of Sgr. A* at the Galactic Centre.
The INTEGRAL Optical Monitoring Camera, OMC, has detected many high energy sources. We have obtained V-band fluxes and light curves for their counterparts. In the cases of previously unknown counterparts, we have searched for characteristic variations in optical sources around the high-energy target position. Results about the Galactic Bulge Monitoring, INTEGRAL Gamma-Ray sources (IGR), and other high energy sources are presented.
We have reexamined our previously published data to search for evidence of correlations between the rates for the alpha, beta-minus, beta-plus, and electron-capture decays of 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am and the Earth-Sun distance. We find no evidence for such correlations and set limits on the possible amplitudes of such correlations substantially smaller than those observed in previous experiments.
We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1-35 microns and combining a wide range of materials based on spectral studies of comets and debris disks. In order of their contribution to the mid-infrared emission, the most abundant minerals for G29-38 are amorphous carbon, amorphous and crystalline silicates, water ice, and metal sulfides. The amorphous C can be equivalently replaced by other materials (like metallic Fe) with featureless infrared spectra. The best-fitting crystalline silicate is Fe-rich pyroxene. In order to absorb enough starlight to power the observed emission, the disk must either be much thinner than the stellar radius (so that it can be heated from above and below) or it must have an opening angle wider than 2 degrees. A `moderately optically thick' torus model with mass 2x10^19 g fits the spectrum well. A physically thin (less than the white dwarf radius) and optically thick disk can contribute to the near-infrared continuum only; such a disk cannot explain the longer-wavelength continuum or strong silicate features. The silicate composition contains minerals found from cometary spectra and meteorites, but Fe-rich pyroxene is more abundant than enstatite (Mg-rich pyroxene) or forsterite (Mg-rich olivine) in G29-38, in contrast to what is found in most comet or meteorite mineralogies. Enstatite meteorites may be the most similar solar system materials to the G29-38 dust. Finally, we suggest the surviving core of a `hot jupiter' as an alternative (neither cometary nor asteroidal) origin for the debris, though further theoretical work is needed to determine if this hypothesis is viable.
The rate of quasi-stationary, two-dimensional magnetic reconnection is calculated in the framework of incompressible Hall magnetohydrodynamics (MHD). The calculation is based on the solution of Hall-MHD equations that include Hall and electron pressure terms for electric current. These equations are solved in a local region across the reconnection electron layer, including only the upstream region and the layer center. In the case when the ion inertial length d_i is larger than the Sweet-Parker reconnection layer thickness, the dimensionless reconnection rate is found to be independent of the electrical resistivity and equal to d_i/L, where L is the scale length of the external magnetic field in the upstream region outside the electron layer.
The Kolmogorov stochasticity parameter (KSP) is applied to quantify the degree of randomness (stochasticity) in the temperature maps of the Cosmic Microwave Background radiation maps. It is shown that, the KSP for the WMAP5 maps is about twice higher than that of the simulated maps for the concordance \Lambda- CDM cosmological model, implying the existence of a randomizing effect not taken into account in the model. As was revealed recently, underdense regions in the large scale matter distributions, i.e the voids, possess hyperbolic and hence randomizing properties. The degree of randomness for the Cold Spot appears to be about twice higher than the average over the sky, which supports the void nature of the Cold Spot. KSP then acts as a quantitative tracer of the voids via CMB.
A new multi-frequency synthesis algorithm for reconstructing images from multi-frequency VLBI data is proposed. The algorithm is based on a generalized maximum-entropy method, and makes it possible to derive an effective spectral correction for images over a broad frequency bandwidth, while simultaneously reconstructing the spectral-index distribution over the source. The results of numerical simulations demonstrating the capabilities of the algorithm are presented.
Due to their short lifetimes but their enormous energy release in all stages of their lives massive stars are the major engines for the comic matter circuit. They affect not only their close environment but are also responsible to drive mass flows on galactic scales. Recent 2D models of radiation-driven and wind-blown HII regions are summarized which explore the impact of massive stars to the interstellar medium but find surprisingly small energy transfer efficiencies while an observable Carbon self-enrichment in the Wolf-Rayet phase is detected in the warm ionized gas. Finally, the focus is set on state-of-the-art modelling of HII regions and its present weaknesses with respect to uncertainties and simplifications but on a perspective of the requested art of their modelling in the 21st century.
We analyse the evolution of the Intergalactic Medium (IGM) by means of an extended set of large box size hydrodynamical simulations which include pre-heating. We focus on the properties of the z~2 Lyman-alpha forest and on the population of clusters and groups of galaxies at z=0. We investigate the distribution of voids in the Lyman-alpha flux and the entropy-temperature relation of galaxy groups, comparing the simulation results to recent data from high-resolution quasar spectra and from X-ray observations. Pre-heating is included through a simple phenomenological prescription, in which at z=4 the entropy of all gas particles, whose overdensity exceeds a threshold value delta_h is increased to a minimum value K_fl. While the entropy level observed in the central regions of galaxy groups requires a fairly strong pre-heating, with K_fl>100 keV cm^2, the void statistics of the Lyman-alpha forest impose that this pre-heating should take place only in relatively high-density regions, in order not to destroy the cold filaments that give rise to the forest. We conclude that any injection of non-gravitational energy in the diffuse baryons should avoid low-density regions at high redshift and/or take place at relatively low redshift.
Three-dimensional neutral hydrogen mapping using the redshifted 21 cm line has recently emerged as a promising cosmological probe. Within the framework of slow-roll reconstruction, we analyze how well the inflationary potential can be reconstructed by combining data from 21 cm experiments and cosmic microwave background data from the Planck satellite. We consider inflationary models classified according to the amplitude of their tensor component, and show that 21 cm measurements can significantly improve constraints on the slow-roll parameters and determine the shape of the inflationary potential.
The existence of old dispersed stellar groups within the Milky Way disk is still controversial. Are they the debris of ancient star-forming aggregates, or short-lived artifacts of dynamical origin? With detailed elemental abundance measurements from high quality spectroscopic data, we show that at least one such old dispersed stellar group is a true relic of an earlier phase of star formation. The identification of other such relic structures will provide essential information for probing the evolutionary history of the Milky Way disk.
The evolution of galactic disks from their early stages is dominated by gasdynamical effects such as gas infall, galactic fountains, and galactic outflows, and further more. The influence of these processes is only understandable in the framework of diverse gas phases differing in their thermal energies, dynamics, and element abundances. To trace the temporal and chemical evolution of galactic disks, it is therefore essential to model the interstellar gasdynamics combined with stellar dynamics, the interactions between gas phases, and star-gas mass and energy exchanges as detailed as possible. This article reviews the potential of state-of-the-art numerical schemes like Smooth-Particle and grid-based hydrodynamics as well as the inherent processes as of star-formation criteria and feedback, energy deposit and metal enrichment by stars and on the influence of gas-phase interactions on the galactic gas dynamics and chemistry.
We measure four different types of alignment signals using the galaxy groups of the Sloan Digital Sky Survey Data Release 4 to probe the impact of large scale environment on the distribution of satellite galaxies, on the the orientation of the central and satellite galaxies: (1) the alignment between the distributions of the satellites relative to the direction of the nearest neighbor group (NNG); (2) the alignment between the major axis direction of the central galaxy of the host group (HG) and the direction of the NNG; (3) the alignment between the two major axes of the central galaxies of the HG and NNG; and (4) the alignment between the major axes of the satellites of the HG and the direction of the NNG. We find strong alignment signals of satellite distribution and orientation of central galaxy relative to the direction of the NNG even when the NNG locates beyond $3r_{\rm vir}$ of the host group. The alignment signals are stronger for groups that are more massive and with early type central galaxies. For the orientation of satellite galaxies, however, we do not find any significant alignment signals relative to the direction of the NNG. From these four types of the alignment measures, we conclude that the large scale environment traced by the nearby group mainly impacts the shape of the host dark matter halo, hence impacts the distribution of satellite galaxies and the orientation of central galaxies. Apart from these, there is additional impacts by the large scale environment directly onto the distribution of satellite galaxies.
We discuss the results of the radio studies of the X-ray binaries with relativistic jets. We carried out a multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the microquasars SS433, GRS1915+105, and Cyg X-3 with the RATAN-600 radio telescope during the recent sets from 1 November 2006 to 31 August 2008. From December 2005 radio emission of Cyg X-3 after four years relatively quiescent levels (100-200 mJy) dropped down to $\sim$20 mJy, and then we detected a lot of bright radio flaring events (1-20 Jy) followed the very variable (from 0 to 0.5 crabs) 15-50 keV X-ray emission, which was monitored in the Swift/BAT ASM program. Again from December 2007 to March 2008 we have daily measured almost quiescent fluxes from Cyg X-3 but in April 2008 a bright radio flare with clear synchrotron self-absorption was detected. We detected several bright short-term flares from GRS 1915+105 which could be associated with active soft X-ray events. In intense measurements of SS433 fluxes (often mutually with X-ray and optical observations) we detected massive ejections during powerful flares. We discuss the various spectral and temporal characteristics of the light curves from the microquasars. Monitoring of the flaring radio emission is a good tracer of jet activity X-ray binaries.
The Optical Monitoring Camera on-board INTEGRAL (OMC) provides Johnson V band photometry of any potentially variable source within its field of view. Taking advantage of the INTEGRAL capabilities allowing the simultaneous observation of different kind of objects in the optical, X and gamma rays bands, we have performed a study of the optical counterparts of different high-energy sources. Up to now, OMC has detected the optical counterpart for more than 100 sources from the High Energy Catalog (Ebisawa et al., 2003). The photometrically calibrated light curves produced by OMC can be accessed through our web portal at: this http URL
Hinode discovered a beautiful giant jet with both cool and hot components at the solar limb on 2007 February 9. Simultaneous observations by the Hinode SOT, XRT, and TRACE 195 satellites revealed that hot (5x10^6 K) and cool (10^4 K) jets were located side by side and that the hot jet preceded the associated cool jet (1-2 minutes). A current-sheet-like structure was seen in optical (Ca IIH), EUV (195A), and soft X-ray emissions, suggesting that magnetic reconnection is occurring in the transition region or upper chromosphere. Alfven waves were also observed with Hinode SOT. These propagated along the jet at velocities of 200 km/s with amplitudes (transverse velocity) of 5-15 km/s and a period of 200 s. We performed two-dimensional MHD simulation of the jets on the basis of the emerging flux-reconnection model, by extending Yokoyama and Shibata's model. We extended the model with a more realistic initial condition (10^6 K corona) and compared our model with multiwavelength observations. The improvement of the coronal temperature and density in the simulation model allowed for the first time the reproduction of the structure and evolution of both the cool and hot jets quantitatively, supporting the magnetic reconnection model. The generation and the propagation of Alfven waves are also reproduced self-consistently in the simulation model.
The primary challenge of GOLF-NG (Global Oscillations at Low Frequency New Generation) is the detection of the low-frequency solar gravity and acoustic modes, as well as the possibility to measure the high-frequency chromospheric modes. On June 8th 2008, the first sunlight observations with the multichannel resonant GOLF-NG prototype spectrometer were obtained at the Observatorio del Teide (Tenerife). The instrument performs integrated (Sun-as-a-star), Doppler velocity measurements, simultaneously at eight different heights in the D1 sodium line profile, corresponding to photospheric and chromospheric layers of the solar atmosphere. In order to study its performances, to validate the conceived strategy, and to estimate the necessary improvements, this prototype has been running on a daily basis over the whole summer of 2008 at the Observatorio del Teide. We present here the results of the first GOLF-NG observations, clearly showing the characteristics of the 5-minute oscillatory signal at different heights in the solar atmosphere. We compare these signals with simultaneous observations from GOLF/SOHO and from the Mark-I instrument -- a node of the BiSON network, operating at the same site.
In this paper we analyse the relations between a previously described oblate Jaffe model for an ellipsoidal galaxy and the observed quantities for NGC 2974, and obtain the length and velocity scales for a relevant elliptical galaxy model. We then derive the finite total mass of the model from these scales, and finally find a good fit of an isotropic oblate Jaffe model by using the Gauss-Hermite fit parameters and the observed ellipticity of the galaxy NGC 2974. The model is also used to predict the total luminous mass of NGC 2974, assuming that the influence of dark matter in this galaxy on the image, ellipticity and Gauss-Hermite fit parameters of this galaxy is negligible within the central region, of radius $0.5R_{\rm e}.$
We report the detection of CO molecular line emission in the z=4.5 millimeter-detected galaxy COSMOS_J100054+023436 (hereafter: J100+0234) using the IRAM Plateau de Bure interferometer (PdBI) and NRAO's Very Large Array (VLA). The CO(4-3) line as observed with PdBI has a full line width of ~1000 km/s, an integrated line flux of 0.66 Jy km/s, and a CO luminosity of 3.2e10 L_sun. Comparison to the 3.3sigma detection of the CO(2-1) line emission with the VLA suggests that the molecular gas is likely thermalized to the J=4-3 transition level. The corresponding molecular gas mass is 2.6e10 M_sun assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blue-shifted line peaks and the line width a dynamical mass of 1.1e11 M_sun is estimated assuming a merging scenario. The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5'' from the previously detected Ly$\alpha$ emission. J1000+0234 exhibits very typical properties for lower redshift (z~2) sub-millimeter galaxies (SMGs) and thus is very likely one of the long sought after high redshift (z>4) objects of this population. The large CO(4-3) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the Big Bang. Given its large star formation rate (SFR) of >1000 M_sun/yr and molecular gas content this object could be the precursor of a 'red-and-dead' elliptical observed at a redshift of z=2.
We report on the first results obtained with the IceTop air shower array on the cosmic ray energy spectrum and mass composition in the range of 1 PeV to 80 PeV. IceTop is the surface detector of the IceCube neutrino telescope currently under construction at the South Pole. A high sensitivity to the primary mass composition was observed by reconstructing showers at different zenith angles. Assuming only protons or iron nuclei as primary particles yields significantly different energy spectra for different zenith angle ranges, while only models with mixed composition, like the poly-gonato model, lead to the expected isotropic flux. The prospects of composition measurements with different, alternative methods using the full IceCube detector are also discussed.
We have computed a spherically symmetric model for the interaction of matter ejected during the outburst of a classical nova with the stellar wind from its optical component.This model is used to describe the intense X-ray outburst (the peak 3-20 keV flux was ~2 Crab) of the binary system CI Camelopardalis in 1998. According to our model, the stellar wind from the optical component heated by a strong shock wave produced when matter is ejected from the white dwarf as the result of a thermonuclear explosion on its surface is the emission source in the standard X-ray band. Comparison of the calculated and observed time dependences of the mean radiation temperature and luminosity of the binary system during its outburst has yielded very important characteristics of the explosion.We have been able to measure the velocity of the ejected matter immediately after the onset of the explosion for the first time: it follows from our model that the ejected matter had a velocity of ~2700 km/s even on 0.1-0.5 day after the outburst onset and it flew with such a velocity for the first 1-1.5 day under an external force, possibly, the radiation pressure from the white dwarf. Subsequently, the matter probably became transparent and began to decelerate. The time dependence of the mean radiation temperature at late expansion phases has allowed us to estimate the mass of the ejected matter, ~10^{-7}-10^{-6} Msun. The mass loss rate in the stellar wind required to explain the observed peak luminosity of the binary system during its outburst has been estimated to be dM/dt ~(1-2)x10^{-6} Msun/yr.
The main goals of the HELAS local helioseismology network activity are to consolidate this field of research in Europe, to organise scientific workshops, and to facilitate the distribution of observations and data analysis software. Most of this is currently accomplished via a dedicated website at this http URL . In this paper we list the outreach material, observational data, analysis tools and modelling tools currently available from the website and describe the focus of the scientific workshops and their proceedings.
We investigate the physical properties of the gas in the disks around the
Herbig Ae/Be stars HD 97048 and HD 100546.
Using high-spectral-resolution 4.6-5.1 $\mu$m spectra containing fundamental
CO emission taken with the CRIRES on the VLT, we probe the physical properties
of the circumstellar gas and model the kinematics of the emission lines. By
using spectro-astrometry on the spatially resolved targets, we constrain the
physical size of the emitting regions in the disks.}
We resolve, spectrally and spatially, the emission of the $^{13}CO$ v(1-0)
vibrational band and the $^{12}CO$ v(1-0), v(2-1), v(3-2) and v(4-3)
vibrational bands in both targets, as well as the $^{12}CO$ v(5-4) band in HD
100546. The spectro-astrometry yields shifts in the photo center for all
spatially resolved vibrational lines in HD 100546 up to between 9 and 10 AU,
and for HD 97048 up to 16 AU for the v(2-1) and v(3-2) vibrational lines.
Modeling of the CO emission yields inner radii of the CO emitting region of 12
and 15 AU for HD 97048 and HD 100546 respectively. The fact that continuum
emission is present within these radii in both stars and gaseous [OI] emission
was previously detected in both targets at smaller radii suggests that CO may
be effectively destroyed at small radii in the surface layers of the disks
surrounding intermediate-mass young stars. The CO emitting regions of both
stars are comparable, but the continuum emission of HD 100546 originates from
an area half the size of the HD 97048 continuum emission.
We present observations and analysis of time-series spectroscopy and
photometry of the pulsating subdwarf B star PG 1219+534 (KY UMa). Subdwarf B
stars are blue horizontal branch stars which have shed most of their hydrogen
envelopes. Pulsating subdwarf B stars allow a probe into this interesting phase
of evolution. Low resolution spectra were obtained at the Nordic Optical
Telescope and Kitt Peak National Observatory, and photometric observations were
obtained at MDM and Baker observatories in 2006. We extracted radial velocity
and equivalent width variations from several Balmer and He I lines in
individual spectra. The pulsation frequencies were separated via phase binning
to detect line-profile variations in Balmer and helium lines, which were
subsequently matched to atmospheric models to infer effective temperature and
gravity changes throughout the pulsation cycle.
From the photometry we recovered the four previously observed frequencies and
detected a new fifth frequency. From the spectra we directly measured radial
velocity and equivalent width variations for the four main frequencies and from
atmospheric models we successfully inferred temperature and gravity changes for
these four frequencies. We compared amplitude ratios and phase differences of
these quantities and searched for outliers which could be identified as
high-degree modes. These are the first such measurements for a "normal"
amplitude pulsating subdwarf B star, indicating that spectroscopic studies can
benefit the majority of pulsating subdwarf B stars.
We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. First results are presented of an analysis of 20 hours of observation data for NuMoon project using the Westerbork Synthesis Radio Telescope to search for short radio pulses from the Moon. A limit on the neutrino flux is set that is a factor four better than the current one (based on FORTE).
We present a dynamical model of the high mass X-ray binary LMC X-1 based on high-resolution optical spectroscopy and extensive optical and near-infrared photometry. From our new optical data we find an orbital period of P=3.90917 +/- 0.00005 days. We present a refined analysis of the All Sky Monitor data from RXTE and find a period of P=3.9093 +/- 0.0008 days, which is consistent with the optical period. A simple model of Thomson scattering in the stellar wind accounts for the modulation seen in the X-ray light curves. The V-K color of the star (1.17 +/- 0.05) implies A_V=2.28 +/- 0.06, which is much larger than previously assumed. For the secondary star we measure a radius of R_2=17.0 +/- 0.8 solar radii and a projected rotational velocity of V_{rot}*sin(i)= 129.9 +/- 2.22 km/sec. Using these measured properties to constrain the dynamical model, we find an orbital eccentricity of e=0.0256 +/- 0.0066, an inclination of i=37.00 +/- 1.87 deg, a secondary star mass of M_2=30.62 +/- 3.22 solar masses, and a black hole mass of 10.30 +/- 1.34 solar masses. Although the eccentricity is nonzero at the ~3sigma level, we believe more data should be obtained in order to establish the eccentric nature of the orbit, given that the difference between the light and velocity curves of the best-fitting eccentric model and the best-fitting circular model is very subtle. The present location of the secondary star in a temperature-luminosity diagram is consistent with that of a star with an initial mass of 35 solar masses that is 5 Myr past the zero-age main sequence. The star nearly fills its Roche lobe (~90% or more), and owing to the rapid change in radius with time in its present evolutionary state, it will encounter its Roche lobe and begin unstable mass transfer on a timescale of a few hundred thousand years.
Recently, a very large clustering length has been measured for quasars at a redshift of z~4. In combination with the observed quasar luminosity function we assess the implications of this clustering for the relationship between quasar luminosity and dark matter halo mass. Our analysis allows for non-linearity and finite scatter in the relation between quasar luminosity and halo mass, as well as a luminosity dependent quasar lifetime. The additional novel ingredient in our modelling is the allowance for an excess in the observed bias over the underlying halo bias owing to the merger driven nature of quasar activity. We find that the observations of clustering and luminosity function can be explained only if both of the following conditions hold: (i) The luminosity to halo mass ratio increases with halo mass; (ii) The observed clustering amplitude is in excess of that expected solely from halo bias. The latter result is statistically significant at the 99% level. Taken together, the observations provide compelling evidence for merger driven quasar activity, with a black-hole growth that is limited by feedback. In difference from previous analyses, we show that there could be scatter in the luminosity halo mass relation of up to 1 dex, and that quasar clustering can not be used to estimate the quasar lifetime.
We present the color-magnitude and color-stellar mass diagrams for galaxies with z_phot < ~2, based on a K < 22 (AB) catalog of the Extended Chandra Deep Field South (ECDFS) from the MUltiwavelength Survey by Yale-Chile (MUSYC). Our main sample of 7840 galaxies contains 1297 M_* > 10^11 M_Sol galaxies in the range 0.2 < z_phot < 1.8. We show empirically that this catalog is approximately complete for M_* > 10^11 M_Sol galaxies for z_phot < 1.8. For this mass-limited sample, we show that the locus of the red sequence color-stellar mass relation evolves as Del(u-r) ~ (-0.44+/-0.02) z_phot for z_phot < ~1.2. For z_phot > ~1.3, however, we are no longer able to reliably distinguish red and blue subpopulations from the observed color distribution; we show that this would require much deeper near infrared data. At 1.5 < z_phot <1.8, the comoving number density of M_* > 10^11 M_Sol galaxies is ~50% of the local value, with a red fraction of ~33%. Making a parametric fit to the observed evolution, we find n_tot(z) ~ (1+z_phot)^(-0.52+/-0.12(+/-0.20)). We find stronger evolution in the red fraction: f_red(z) ~ (1+z_phot)^(-1.17+/-0.18(+/-0.21)). Through a series of sensitivity analyses, we show that the most important sources of systematic error are: 1. systematic differences in the analysis of the z~0 and z>>0 samples; 2. systematic effects associated with details of the photometric redshift calculation; and 3. uncertainties in the photometric calibration. With this in mind, we show that our results based on photometric redshifts are consistent with a completely independent analysis which does not require redshift information for individual galaxies. Our results suggest that, at most, 1/5 of local red sequence galaxies with M_* >10^11 M_Sol were already in place at z ~ 2.
We have investigated evolution of magneto-rotational instability (MRI) in protoplanetary disks that have radially non-uniform magnetic field such that stable and unstable regions coexist initially, and found that a zone in which the disk gas rotates with a super-Keplerian velocity emerges as a result of the non-uniformly growing MRI turbulence. We have carried out two-dimensional resistive MHD simulations with a shearing box model. We found that if the spatially averaged magnetic Reynolds number, which is determined by widths of the stable and unstable regions in the initial conditions and values of the resistivity, is smaller than unity, the original Keplerian shear flow is transformed to the quasi-steady flow such that more flattened (rigid-rotation in extreme cases) velocity profile emerges locally and the outer part of the profile tends to be super-Keplerian. Angular momentum and mass transfer due to temporally generated MRI turbulence in the initially unstable region is responsible for the transformation. In the local super-Keplerian region, migrations due to aerodynamic gas drag and tidal interaction with disk gas are reversed. The simulation setting corresponds to the regions near the outer and inner edges of a global MRI dead zone in a disk. Therefore, the outer edge of dead zone, as well as the inner edge, would be a favorable site to accumulate dust particles to form planetesimals and retain planetary embryos against type I migration.
Modeling the variability of the solar spectral irradiance is a key factor for understanding the solar influence on the climate of the Earth. As a first step to calculating the solar spectral irradiance variations we reproduce the solar spectrum for the quiet Sun over a broad wavelength range with an emphasis on the UV. We introduce the radiative transfer code COSI which calculates solar synthetic spectra under conditions of non-local thermodynamic equilibrium (NLTE). A self-consistent simultaneous solution of the radiative transfer and the statistical equation for the level populations guarantees that the correct physics is considered for wavelength regions where the assumption of local thermodynamic equilibrium (LTE) breaks down. The new concept of iterated opacity distribution functions (NLTE-ODFs), through which all line opacities are included in the NLTE radiative transfer calculation, is presented. We show that it is essential to include the line opacities in the radiative transfer to reproduce the solar spectrum in the UV. Through the implemented scheme of NLTE-ODFs the COSI code is successful in reproducing the spectral energy distribution of the quiet Sun.
In the past few decades, several models have predicted an energy-dependence of the speed of light in the context of quantum gravity. For cosmological sources such as active galaxies, this minuscule effect can add up to measurable photon-energy dependent time lags. In this paper a search for such time lags during the H.E.S.S. observations of the exceptional very high energy flare of the active galaxy PKS 2155-304 on 28 July in 2006 is presented. Since no significant time lag is found, lower limits on the energy scale of speed of light modifications are derived.
Using the modern equations of state derived from microscopic calculations, we have calculated the neutron star structure. For the neutron star, we have obtained a minimum mass about $0.1 {\rm M_{\odot}}$ which is nearly independent of the equation of state, and a maximum mass between $1.47 {\rm M_{\odot}}$ and $1.98 {\rm M_{\odot}}$ which is strongly dependent on the equation of state. It is shown that among the equations of state of neutron star matter which we have used, the stiffest one leads to higher maximum mass and radius and lower central density. It is seen that the given maximum mass for the Reid-93 equation of state shows a good consistency with the accurate observations of radio pulsars. We have indicated that the thickness of neutron star crust is very small compared to the predicted neutron star radius.
Modern N-body techniques for planetary dynamics are generally based on symplectic algorithms specially adapted to the Kepler problem. These methods have proven very useful in studying planet formation, but typically require the timestep for all objects to be set to a small fraction of the orbital period of the innermost body. This computational expense can be prohibitive for even moderate particle number for many physically interesting scenarios, such as recent models of the formation of hot exoplanets, in which the semimajor axis of possible progenitors can vary by orders of magnitude. We present new methods which retain most of the benefits of the standard symplectic integrators but allow for radial zones with distinct timesteps. These approaches should make simulations of planetary accretion with large dynamical range tractable. As proof of concept we present preliminary science results from an implementation of the algorithm as applied to an oligarchic migration scenario for forming hot Neptunes.
Cassini-Huygens data are used to re-examine the potential sources of the D/H enhancement over solar, measured in methane, in Titan's atmosphere. Assuming that the system is closed with respect to carbon, the use of constraints from the Huygens probe for the determination of the current mass of atmospheric methane and the most up-to-date determination of D/H from Cassini/CIRS infrared spectra allow us to show that photochemical enrichment of deuterium is not sufficient to be the sole mechanism yielding the measured D/H value. A possible fractionation between CH3D and CH4 during the escape process may slightly enhance the deuterium enrichment, but is not sufficient to explain the observed D/H value over the range of escape values proposed in the literature. Hence, alternative mechanisms such as a primordial deuterium enrichment must be combined with the photochemical enrichment in Titan's atmosphere in order to explain its current D/H value.
The use of Type Ia supernovae as distance indicators led to the discovery of the accelerating expansion of the universe a decade ago. Now that large second generation surveys have significantly increased the size and quality of the high-redshift sample, the cosmological constraints are limited by the currently available sample of ~50 cosmologically useful nearby supernovae. The Nearby Supernova Factory addresses this problem by discovering nearby supernovae and observing their spectrophotometric time development. Our data sample includes over 2400 spectra from spectral timeseries of 185 supernovae. This talk presents results from a portion of this sample including a Hubble diagram (relative distance vs. redshift) and a description of some analyses using this rich dataset.
I describe how the dynamics of galactic disks can be inferred by imaging and spectroscopy. Next I demonstrate that the decomposition of the rotation curves of spiral galaxies into the contributions by the various components of the galaxies is highly degenerate. Constraints on the decomposition can be found by considering implications for the dynamics of the galactic disks. An important diagnostic is the Toomre Q stability parameter which controls the stability of a galactic disk against local Jeans collapse. I also show how the density wave theory of galactic spiral arms can be employed to constrain the mass of a galactic disk. Applying both diagnostics to the example of NGC 2985 and discussing also the implied mass-to-light ratio I demonstrate that the inner parts of the galaxy, where the optical disk resides, are dominated by baryons. When I apply this method to the disks of low surface brightness galaxies, I find unexpectedly high mass-to light ratios. These could be explained by population synthesis models which assume a bottom heavy initial mass function similar to the recently proposed `integrated galactic initial mass function'.
An energy threshold of (220$\pm$10) eV was achieved at an efficiency of 50% with a four-channel ultra-low-energy germanium detector each with an active mass of 5 g\cite{wimppaper}. This provides a unique probe to WIMP dark matter with mass below 10 GeV. With low background data taken at the Kuo-Sheng Laboratory, constraints on WIMPs in the galactic halo were derived. Both spin-independent WIMP-nucleon and spin-dependent WIMP-neutron bounds improve over previous results for WIMP mass between 3$-$6 GeV. These results, together with those on spin-dependent couplings, will be presented. Sensitivities for full-scale experiments were projected. This detector technique makes the unexplored sub-keV energy window accessible for new neutrino and dark matter experiments.
The availability of high-quality spectra for a large number of galaxies in the SDSS survey allows for a more sophisticated extraction of information about their stellar populations than, e.g., the luminosity weighted age. Indeed, sophisticated and robust techniques to fully analyze galaxy spectra have now reached enough maturity as to trust their results and findings. By reconstructing the star formation and metallicity history of galaxies from the SDSS fossil record and analyzing how it relates to its environment, we have learned how to classify galaxies: to first order the evolution of a galaxy is determined by its present stellar mass, which in turn seems to be governed by the merger rate of dark halos.
The longstanding problem of modeling double-mode behaviour of classical pulsators was solved with the incorporation of turbulent convection into pulsation hydrocodes. However, the reasons for the computed double-mode behaviour were never clearly identified. In our recent papers (Smolec & Moskalik 2008a,b) we showed that the double-mode behaviour results from the neglect of negative buoyancy effects in some of the hydrocodes. If these effects are taken into account, no stable non-resonant double-mode behaviour can be found. In these proceedings we focus our attention on the role of negative buoyancy effects in classical Cepheid models.
On the 15th of June 2006, the PAMELA satellite-borne experiment was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The apparatus comprises a time-of-flight system, a silicon-microstrip magnetic spectrometer, a silicon-tungsten electromagnetic calorimeter, an anticoincidence system, a shower tail counter scintillator and a neutron detector. The combination of these devices allows precision studies of the charged cosmic radiation to be conducted over a wide energy range (100 MeV - 100's GeV) with high statistics. The primary scientific goal is the measurement of the antiproton and positron energy spectrum in order to search for exotic sources, such as dark matter particle annihilations. PAMELA is also searching for primordial antinuclei (anti-helium), and testing cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and precision studies of light nuclei and their isotopes. We review the status of the apparatus and present preliminary results concerning antiparticle measurements and dark-matter indirect searches.
Aims: A near-infrared study of the main ionizing star of the ultracompact HII region G23.96+0.15 (IRAS 18317-0757) is presented, along with a re-evaluation of the distance to this source, and a re-assessment of H- and K-band classification diagnostics for O dwarfs; Methods: We have obtained near-IR VLT/ISAAC imaging and spectroscopy of G23.96+0.15, plus archival imaging from UKIRT/UFTI. A spectroscopic analysis was carried out using a non-LTE model atmosphere code; Results: A quantitative H- and K-band classification scheme for O dwarfs is provided, from which we establish an O7.5V spectral subtype for the central star of G23.96+0.15. We estimate an effective temperature of Teff ~ 38 kK from a spectral analysis; Conclusions: A spectroscopic distance of 2.5 kpc is obtained for G23.96+0.15, substantially lower than the kinematic distance of 4.7 kpc, in common with recent studies of other Milky way HII regions. Such discrepancies would be alleviated if sources are unresolved binaries or clusters.
Gamma-ray Bursts are the most powerful objects in the Universe. Discovered in the 1960's as brief flashes of gamma-radiation, we now know they emit across the entire electromagnetic spectrum, are located in distant galaxies and comprise two distinct populations, one of which may originate in the deaths of massive stars. The launch of the Swift satellite in 2004 has brought a flurry of new discoveries, advancing our understanding of these sources and the galaxies that host them. We highlight a number of important results from the Swift era thus far.
Some of the first results are reported from RISE - a new fast camera mounted on the Liverpool Telescope primarily designed to obtain high time resolution light curves of transiting extrasolar planets for the purpose of transit timing. A full and partial transit of WASP-3 are presented, and a Monte Carlo Markov Chain analysis is used to update the parameters from the discovery paper. This results in a planetary radius of 1.29^{+0.05}_{-0.12} R_J and therefore a density of 0.82^{+0.14}_{-0.09} p_J, consistent with previous results. The inclination is 85.07^{+0.15}_{-0.16} deg, in agreement (but with a significant improvement in the precision) with the previously determined value. Central transit times are found to be consistent with the ephemeris given in the discovery paper. However, a new ephemeris calculated using the longer baseline results in T_c(0) = 2454605.55915 +- 0.00023 HJD and P = 1.846835 +- 0.000002 days.
A field star, HD 61199 (V ~ 8), simultaneously observed with Procyon by the MOST (Microvariability & Oscillations of STars) satellite in continuous runs of 34, 17, and 34 days in 2004, 2005, and 2007, was found to pulsate in 11 frequencies in the delta Scuti range with amplitudes from 1.7 down to 0.09 mmag. The photometry also showed variations with a period of about four days. To investigate the nature of the longer period, 45 days of time-resolved spectroscopy was obtained at the Thueringer Landessternwarte Tautenburg in 2004. The radial velocity measurements indicate that HD 61199 is a triple system. A delta Scuti pulsator with a rich eigenspectrum in a multiple system is promising for asteroseismology. Our objectives were to identify which of the stars in the system is the delta Scuti variable and to obtain the orbital elements of the system and the fundamental parameters of the individual components, which are constrained by the pulsation frequencies of the delta Scuti star. Classical Fourier techniques and least-squares multi-sinusoidal fits were applied to the MOST photometry to identify the pulsation frequencies. The groundbased spectroscopy was analysed with least-squares-deconvolution (LSD) techniques, and the orbital elements derived with the KOREL and ORBITX routines. Asteroseismic models were also generated. The photometric and spectroscopic data are compatible with a triple system consisting of a close binary with an orbital period of 3.57 days and a delta Scuti companion (HD 61199,A) as the most luminous component. The delta Scuti star is a rapid rotator with about vsin i = 130 km/s and an upper mass limit of about 2.1 Msun. For the close binary components, we find they are of nearly equal mass, with lower mass limits of about 0.7 Msun.
In order to get a significant Zeeman signature in the polarised spectra of a magnetic star, we usually 'add' the contributions of numerous spectral lines; the ultimate goal is to recover the spectropolarimetric prints of the magnetic field in these line additions. Here we want to clarify the meaning of these techniques of line addition; in particular, we try to interpret the meaning of the 'pseudo-line' formed during this process and to find out why and how its Zeeman signature is still meaningful. We create a synthetic case of lines addition and apply well tested standard solar methods routinely used in the research on magnetism in our nearest star. The results are convincing and the Zeeman signatures well detected; Solar methods are found to be quite efficient also for stellar observations. The Zeeman signatures are unequivocally detected in this multiline approach. We may anticipate the outcome magnetic fields to be reliable well beyond the weak-field approximation. Linear polarisation in the spectra of solar type stars can be detected when the spectral resolution is sufficiently high.
We report on X-ray and soft gamma-ray observations of the black-hole candidate GX 339-4 during its 2007 outburst, performed with the RXTE and INTEGRAL satellites. The hardness-intensity diagram of all RXTE/PCA data combined shows a q-shaped track similar to that observed in previous outbursts.The evolution in the diagram suggested that a transition from hard-intermediate state to soft-intermediate state occurred, simultaneously with INTEGRAL observations performed in March. The transition is confirmed by the timing analysis presented in this work, which reveals that a weak type-A quasi-periodic oscillation (QPO) replaces a strong type-C QPO. At the same time, spectral analysis shows that the flux of the high-energy component shows a significant decrease in its flux. However, we observe a delay (roughly one day) between variations of the spectral parameters of the high-energy component and changes in the flux and timing properties. The changes in the high-energy component can be explained either in terms the high-energy cut-off or in terms of a variations in the reflection component. We compare our results with those from a similar transition during the 2004 outburst of GX 339-4.
We present the result of the observation of the ultra-faint dwarf galaxy Willman 1 performed with the 17 m MAGIC Cherenkov telescope during 15.5 hours between March and May 2008. No significant gamma-ray emission was found above 100 GeV. We derived upper limits of the order of $10^{-12}$ photons cm$^{-2}$ s$^{-1}$ on the integral flux above 100 GeV, which we compare with predictions from several of the established neutralino benchmark models in the mSUGRA parameter space. The neutralino annihilation spectra are defined after including the recently discovered contribution of internal bremsstrahlung from the virtual sparticles that mediate the annihilation. Flux boost factors of three orders of magnitude are required even in the most optimistic scenario to match our upper limits. However, uncertainties in the DM distribution (e.g., presence of substructure in the halo) may significantly reduce such boost estimates. Future observations will likely allow us to improve the derived upper limits probably by up to one order of magnitude so that - at least in some regions - the mSUGRA parameter space may be constrained.
Energetic young pulsars and expanding blast waves (supernova remnants, SNRs) are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 ms, a period derivative of 3.614 x 10-13 s s-1 . Its characteristic age of 104 years is comparable to that estimated for the SNR. It is conjectured that most unidentified Galactic gamma ray sources associated with star-forming regions and SNRs are such young pulsars.
We present results of an ongoing program at the ESO VLT for spectroscopy of BL Lac objects lacking a firm redshift estimate and here we report on 15 objects. For 11 sources we confirm the BL Lac classification, and we determine new redshifts for 3 objects, 1 with weak emission lines (PKS 1057-79, z=0.569) and 2 with absorptions from the host galaxy (RBS 1752, z=0.449; RBS 1915, z=0.243); moreover a sub Damped Lyman Alpha (sub-DLA) system is detected in the direction of the BL Lac PKS 0823-223 (z>=0.911). For the remaining 8 BL Lacs, from the very absence of absorption lines of the host galaxy, lower limits to the redshift are deduced with z_min in the interval 0.20-0.80. The remaining three sources are reclassified as a FSRQ (PKS 1145-676, z=0.210; TXS 2346+052, z=0.419) and a misclassified galactic star (PMNJ 1323-3652).
We explore the multidimensional, multiwavelength selection of quasars from mid-IR (MIR) plus optical data, specifically from Spitzer-IRAC and the Sloan Digital Sky Survey (SDSS). We apply modern statistical techniques to combined Spitzer MIR and SDSS optical data, allowing up to 8-D color selection of quasars. Using a Bayesian selection method, we catalog 5546 quasar candidates to an 8.0um depth of 56uJy over an area of ~24 sq. deg; ~70% of these candidates are not identified by applying the same Bayesian algorithm to 4-color SDSS optical data alone. Our selection recovers 97.7% of known type 1 quasars in this area and greatly improves the effectiveness of identifying 3.5<z<5 quasars. Even using only the two shortest wavelength IRAC bandpasses (3.6 and 4.5um), it is possible to use our Bayesian techniques to select quasars with 97% completeness and as little as 10% contamination. This sample has a photometric redshift accuracy of 93.6% (DeltaZ +/- 0.3), remaining roughly constant when the two reddest MIR bands are excluded. While our methods are designed to find type 1 quasars, as many as 1200 of the objects are likely to be type 2 quasars. Coupling deep optical imaging data (e.g., SDSS "Stripe 82" at g~24), with 2-band Spitzer-IRAC data will enable selection of quasars in significant numbers past the peak of the quasar luminosity function (QLF) to at least z~4. Such a sample will constrain the shape of the QLF and enable quasar clustering studies over the largest L-z range to date, improving our understanding of quasars and their contribution to galaxy evolution.
The Cherenkov light flashes produced by Extensive Air Showers are very short in time. A high bandwidth and fast digitizing readout, therefore, can minimize the influence of the background from the light of the night sky, and improve the performance in Cherenkov telescopes. The time structure of the Cherenkov image can further be used in single-dish Cherenkov telescopes as an additional parameter to reduce the background from unwanted hadronic showers. A description of an analysis method which makes use of the time information and the subsequent improvement on the performance of the MAGIC telescope (especially after the upgrade with an ultra fast 2 GSamples/s digitization system in February 2007) will be presented. The use of timing information in the analysis of the new MAGIC data reduces the background by a factor two, which in turn results in an enhancement of about a factor 1.4 of the flux sensitivity to point-like sources, as tested on observations of the Crab Nebula.
We present observations of an HI cloud complex most likely located in the Virgo galaxy cluster, first reported by Kent et al. (2007). The complex consists of five clouds, detected in the data set of the ALFALFA extragalactic HI survey at Arecibo. The clouds have radial velocities between cz~480 and 610 km/s. At the Virgo cluster distance, they are spread over a projected span of 170 kpc and have HI masses ranging from 0.48 to 1.7 x 10^8 Msun. The overall HI mass of the complex is 5.1 x 10^8 Msun. The clouds' velocity widths vary between 50 and 250 km/s. New results of follow-up aperture synthesis observations conducted with the Very Large Array are also presented, which yield a higher resolution view of two of the clouds in the complex. These two resolved clouds show no evidence of symmetry in the gas distribution or of any ordered motions. The possibility that the complex is a group of primordial objects, embedded in their own dark matter halo is thought to be unlikely. Scenarios in which the clouds have been removed from the disk of a galaxy traveling at high speed through the intracluster medium are considered. The most likely among those is thought to be one where the clouds were separated from NGC 4445 at a time >0.5 Gyr ago. The orbital velocity of the clouds and the putative parent galaxy would now be seen at a relatively large angle with respect to the line of sight.
We use the current weak lensing data to constrain the equation of state of dark energy $w$ and the total mass of massive neutrinos $\sum m_{\nu}$. The constraint on $w$ would be weak if only the current weak lensing data are used. With the addition of other observational data such as the type Ia supernovae, baryon acoustic oscillation, and the high redshift Hubble parameter data $H(z)$ derived from relative galaxy ages to break the degeneracy, the result is significantly improved. For the pure $w$CDM model without massive neutrinos, we find $w=-1.00^{+0.10}_{-0.12}$. For the $w$CDM model with the massive neutrino component, we show that the constraint on $w$ is almost unchanged, there is very little degeneracy between $w$ and $\sum m_{\nu}$. After marginalizing over other parameters, we obtain the probability distribution function of $\sum m_{\nu}$, and find that the upper limit is $\sum m_{\nu} \leq 0.8$ eV at 95.5% confidence level for the combined data sets. Our constraints of $w$ and $\sum m_{\nu}$ are both compatible and comparable with the constraints obtained from the WMAP 5-year data.
We combine Spitzer IRAC mid-infrared (MIR) and Chandra X-ray observations of the dominant galaxies NGC6872 and NGC6876 in the Pavo group with archival optical and HI data to study interaction-induced star formation. In spiral galaxy NGC6872, 8.0 and 5.8 micron nonstellar emission having colors consistent with polycyclic aromatic hydrocarbons (PAHs) is concentrated in clumps in three regions: in a 5 kpc radius outer ring about the center of the spiral galaxy, in a bridge of emission connecting NGC6872's northern spiral arm to IC4970, and along the full extent of NGC6872's tidal arms. PAH emission is correlated with young star clusters and dense HI regions. We find no strong differences in the MIR colors of star-forming regions in the spiral galaxy NGC6872 as a function of position relative to the tidally interacting companion galaxy IC4970. We find 11 very luminous X-ray sources (>~ (0.5 - 5) x 10^{39} ergs/s) clustered to the southwest in NGC6872, near bright star-forming regions. In NGC6872's tidal features, young star clusters form at the boundaries of diffuse X-ray gas, suggesting that stars form as gas stripped by the interactions cools. The nucleus of NGC6872 is a weak X-ray point source (0.5-8 keV luminosity of 8.5 x 10^{39} ergs/s), but there is little evidence in the inner 1 kpc of NGC6872 for PAH emission from recent star formation or nuclear activity. However, a 4 kpc `stream', leading from the outer ring of NGC6872 to the nucleus, may signal transport of interstellar matter into NGC6872's nuclear region. Nonstellar emission, consistent with PAH emission, is also found in the central region of elliptical galaxy NGC6877, companion to dominant Pavo group elliptical NGC6876. However, in the central region of NGC6876, the dust emission is more likely due to silicate emission from old AGB stars.
We present a new model of the blazar gamma-ray luminosity function (GLF) and the spectrum of the extragalactic gamma-ray background (EGRB), which is consistent with the observed distributions of EGRET blazars. The unified sequence of blazar spectral energy distribution (SED) is taken into account to make a non-trivial prediction for the EGRB spectrum and more realistic comparison with the data than previous studies. We then try to explain the EGRB data by the two AGN populations: blazars and non-blazar AGNs that are responsible for the EGRB in the MeV band. We find that ~80% of the EGRB photon flux at >100 MeV can be explained by this model, which is a significantly higher fraction than previous studies. The predicted EGRB spectrum is in agreement with a wide range of the observed data from X-ray to GeV, within the systematic uncertainties in the EGRB determination by EGRET. These results indicate that AGNs including blazars are the primary source of EGRB. Blazars are dominant in EGRB at higher energy bands of >100 MeV, while non-blazar AGNs dominate at <100 MeV. Almost all of the EGRB flux from blazars will be resolved into discrete sources by the Fermi Gamma-ray Space Telescope, while that from non-blazar AGNs will largely remain unresolved. Therefore, comparison between the integrated source counts and diffuse EGRB flux as a function of photon energy will give a simple and clear test of our model. Various quantitative predictions for Fermi observations are also made. Especially, our model predicts 600-1200 blazars in all sky down to 2e-9 photons/cm^2/s (>100 MeV), which is considerably smaller than previous studies. We find that the fraction of EGRB energy flux absorbed in intergalactic medium (IGM) is not large, and the cascade component reprocessed in IGM does not alter the EGRB spectrum.
We present near-infrared long slit and multi-slit spectra of low mass brown dwarf candidates in the Orion Nebula Cluster. The long slit data were observed in the H- & K-bands using NIRI on the Gemini North Telescope. The multi-object spectroscopic observations were made using IRIS2 on the Anglo Australian Telescope at H-band. We develop a spectral typing scheme based on optically calibrated, near infrared spectra of young sources in the Taurus and IC 348 star forming regions with spectral types M3.0 to M9.5. We apply our spectral typing scheme to 52 sources, including previously published UKIRT and GNIRS spectra. 40 objects show strong water absorption with spectral types of M3 to >M9.5. The latest type objects are provisionally classified as early L types. We plot our sources on H-R diagrams overlaid with theoretical pre-main-sequence isochrones. The majority of our objects lie close to or above the 1 Myr isochrone, leading to an average cluster age that is <1 Myr. We find 38 sources lie at or below the hydrogen burning limit (0.075 Msun). 10 sources potentially have masses below the deuterium burning limit (0.012 Msun). We use a Monte Carlo approach to model the observed luminosity function with a variety of cluster age and mass distributions. The lowest chi^2 values are produced by an age distribution centred at 1 Myr, with a mass function that declines at sub-stellar masses according to an M^alpha power law in the range alpha=0.3 to 0.6. We find that truncating the mass function at 0.012 Msun produces luminosity functions that are starved of the faintest magnitudes, even when using bimodal age populations that contain 10 Myr old sources. The results of these Monte Carlo simulations therefore support the existence of a planetary mass population in the ONC.
The Birmingham Solar-Oscillations Network (BiSON) has been collecting data for over 30yrs and so observations span nearly three 11yr solar activity cycles. This allows us to address important questions concerning the solar cycle and its effect on solar oscillations, such as: how consistent is the acoustic behaviour from one cycle to the next? We have used the p-mode frequencies observed in BiSON data from one solar activity cycle (cycle 22) to predict the mode frequencies that were observed in the next activity cycle (cycle 23). Some bias in the predicted frequencies was observed when short 108d time series were used to make the predictions. We also found that the accuracy of the predictions was dependent on which activity proxy was used to make the predictions and on the length of the relevant time series.
In this paper we describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). It consists of a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), a modern data acquisition and control system and the associated infrastructure for operation in the prime focus cage. The focal plane includes of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of view and 12 smaller 2K x 2K CCDs for guiding, focus and alignment. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.
Velocity oscillations "measured" simultaneously at the photosphere and the chromosphere -from time series of spectropolarimetric data in the 10830 A region- of different solar magnetic features allow us to study the properties of wave propagation as a function of the magnetic flux of the structure (i.e. two different-sized sunspots, a tiny pore and a facular region). While photospheric oscillations have similar characteristics everywhere, oscillations measured at chromospheric heights show different amplitudes, frequencies and stages of shock development depending on the observed magnetic feature. The analysis of the power and the phase spectra, together with simple theoretical modeling, lead to a series of results concerning wave propagation within the range of heights of this study. We find that, while the atmospheric cut-off frequency and the propagation properties of the different oscillating modes depend on the magnetic feature, in all the cases the power that reaches the high chromosphere above the atmospheric cut-off comes directly from the photosphere by means of linear vertical wave propagation rather than from non-linear interaction of modes.
It is a clear unique prediction of the cold dark matter paradigm of cosmological structure formation that galaxies form hierarchically and are embedded in massive, extended dark halos teeming with self-bound substructure or "subhalos". The amount and spatial distribution of subhalos around their host provide unique information and clues on the galaxy assembly process and the nature of the dark matter. Here we present results from the Via Lactea INCITE simulation, a one billion particle, one million cpu-hour simulation of the formation and evolution of a Galactic dark matter halo and its substructure population.
H.E.S.S. (High Energy Stereoscopic System), which is designed to detect TeV gamma-rays, is a system of four Imaging Atmospheric Cherenkov Telescopes situated in Namibia. The system has been shown to be very successful in detecting and observing galactic and extra-galactic TeV sources. In order to explore the highest energy end of GRB spectra, a GRB observing program has been established in the H.E.S.S. collaboration. Here we introduce our GRB observing program and report on its current status.
It is currently believed that galaxies were assembled via chaotic hierarchical mergers between massive cold dark matter halos, in which baryonic star forming matter was embedded. One would therefore expect the properties of individual galaxies to be determined by numerous independent factors such as star forming history, merger history, mass, angular momentum, size and environment. It is therefore surprising to find that galaxies actually appear to form an (almost) one parameter family in which galaxy mass is the dominant factor.
We propose an experimental approach to {\it macro}scopically test the Kochen-Specker theorem (KST) with superconducting qubits. This theorem, which has been experimentally tested with single photons or neutrons, concerns the conflict between the contextuality of quantum mechnaics (QM) and the noncontextuality of hidden-variable theories (HVTs). We first show that two Josephson charge qubits can be controllably coupled by using a two-level data bus produced by a Josephson phase qubit. Next, by introducing an approach to perform the expected joint quantum measurements of two separated Josephson qubits, we show that the proposed quantum circuits could demonstrate quantum contextuality by testing the KST at a macroscopic level.
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We have compiled a sample of 699 stars from the recent literature with detailed chemical abundance information (spanning -4.2 < [Fe/H] < +0.3), and we compute their space velocities and Galactic orbital parameters. We identify members of the inner and outer stellar halo populations in our sample based only on their kinematic properties and then compare the abundance ratios of these populations as a function of [Fe/H]. In the metallicity range where the two populations overlap (-2.5 < [Fe/H] < -1.5), the mean [Mg/Fe] of the outer halo is lower than the inner halo by ~0.1 dex. For [Ni/Fe] and [Ba/Fe], the star-to-star abundance scatter of the inner halo is consistently smaller than in the outer halo. The [Na/Fe], [Y/Fe], [Ca/Fe], and [Ti/Fe] ratios of both populations show similar means and levels of scatter. Our inner halo population is chemically homogeneous, suggesting that a significant fraction of the Milky Way stellar halo originated from a well-mixed ISM. In contrast, our outer halo population is chemically diverse, suggesting that another significant fraction of the Milky Way stellar halo formed in remote regions where chemical enrichment was dominated by local supernova events. We find no abundance trends with maximum radial distance from the Galactic center or maximum vertical distance from the Galactic disk. We also find no common kinematic signature for groups of metal-poor stars with peculiar abundance patters, such as the alpha-poor stars or stars showing unique neutron-capture enrichment patterns. Several stars and dSph systems with unique abundance patterns spend the majority of their time in the distant regions of the Milky Way stellar halo, suggesting that the true outer halo of the Galaxy may have little resemblance to the local stellar halo.
The late-time growth of large scale structures (LSS) is imprinted in the CMBR anisotropy through the Integrated Sachs Wolfe (ISW) effect. This is perceived to be a very important observational probe of dark energy. Future observations of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI) distribution hold the potential of probing the LSS over a large redshift range. We have investigated the possibility of detecting the ISW through cross-correlations between the CMBR anisotropies and redshifted 21-cm observations. Assuming that the HI traces the dark matter, we find that the ISW-HI cross-correlation angular power spectrum at an angular multipole l is proportional to the dark matter power spectrum evaluated at the comoving wave number l/r, where r is the comoving distance to the redshift from which the HI signal originated. The amplitude of the cross-correlation signal depends on parameters related to the HI distribution and the growth of cosmological perturbations. However the cross-correlation is extremely weak as compared to the CMBR anisotropies and the predicted HI signal. As a consequence the cross-correlation signal is smaller than the cosmic variance, and a statistically significant detection is not possible.
High-resolution simulations of cosmological structure formation indicate that dark matter substructure in dense environments, like groups and clusters, may survive for a long time. These dark matter subhalos are the likely hosts of galaxies. We examine the small-scale spatial clustering of subhalo major mergers at high redshift using high-resolution N-body simulations of cosmological volumes. Recently merged, massive subhalos exhibit enhanced clustering on scales ~100-300 kpc/h, relative to all subhalos of the same infall mass, for a short time after a major merger (< 500 Myr). The small-scale clustering enhancement is smaller for lower mass subhalos, which also show a deficit on scales just beyond the excess. Halos hosting recent subhalo mergers tend to have more subhalos; for massive subhalos the excess is stronger and it tends to increase for the most massive host halos. The subhalo merger fraction is independent of halo mass for the scales we probe. In terms of satellite and central subhalos, the merger increase in small-scale clustering for massive subhalos arises from recently merged massive central subhalos having an enhanced satellite population. Our mergers are defined via their parent infall mass ratios. Subhalos experiencing major mass gains also exhibit a small-scale clustering enhancement, but these correspond to two-body interactions leading to two final subhalos, rather than subhalo coalescence.
We present limits on the ejection of old-population HVS from a sample of over 290,000 stars selected from the SDSS. We derive the speed at the solar circle from the measured positions and radial velocities by assuming a radial orbit and adopting a simple isothermal model of the Galactic halo, which enables us to identify candidate bound and unbound ejectees. We find 4 candidate bound F-stars from this sample, all with negative Galactocentric radial velocity (i.e., returning toward the GC). We additionally find 2 candidate unbound stars (one F and one G), however, existing proper motion measurements make these unlikely to be emerging from the GC. These data place an upper limit on the rate of ejection of old-population stars from the GC of ~45/Myr. Comparing to the rate for more massive B-star ejectees of ~0.5/Myr, our limit on the rate of ejection of old-population HVS shows that the mass function at the GC is not bottom-heavy and is consistent with being normal. Future targeted surveys of old-population HVS could determine if it is indeed top-heavy.
We present a study of the host galaxies of AGN selected from the zCOSMOS survey to establish if accretion onto supermassive black holes and star formation are explicitly linked up to z~1. We identify 152 galaxies that harbor AGN, based on XMM observations of 7543 galaxies (i<22.5). Star formation rates (SFRs), including those weighted by stellar mass, are determined using the [OII]3727 emission-line, corrected for an AGN contribution. We find that the majority of AGN hosts have significant levels of star formation with a distribution spanning ~1-100 Msun yr^-1. The close association between AGN activity and star formation is further substantiated by an increase in the AGN fraction with the youthfulness of their stars as indicated by the rest-frame color (U-V) and spectral index Dn(4000); we demonstrate that mass-selection alleviates an artifical peak falling in the transition region when using luminosity-limited samples. We also find that the SFRs of AGN hosts evolve with cosmic time in a manner that closely mirrors the overall galaxy population and explains the low SFRs in AGNs (z<0.3) from the SDSS. We conclude that the conditions most conducive for AGN activity are a massive host galaxy and a large reservoir of gas. Furthermore, a direct correlation between mass accretion rate onto SMBHs and SFR is shown to be weak although the average ratio is constant with redshift, effectively shifting the evidence for a co-evolution scenario in a statistical manner to smaller physical scales. Our findings illustrate an intermittent scenario with an AGN lifetime substantially shorter than that of star formation and underlying complexities regarding fueling over vastly different physical scales yet to be determined [Abridged].
The radial density profile of dark matter structures has been observed to have an almost universal behaviour in numerical simulations, however, the physical reason for this behaviour remains unclear. It has previously been shown that if the pseudo phase-space density, rho/sigma_d^epsilon, is a beautifully simple power-law in radius, with the "golden values" epsilon=3 and d=r (i.e., the phase-space density is only dependent on the radial component of the velocity dispersion), then one can analytically derive the radial variation of the mass profile, dispersion profile etc. That would imply, if correct, that we just have to explain why rho/sigma^3_r ~r^{-alpha}, and then we would understand everything about equilibrated DM structures. Here we use a set of simulated galaxies and clusters of galaxies to demonstrate that there are no such golden values, but that each structure instead has its own set of values. Considering the same structure at different redshifts shows no evolution of the phase-space parameters towards fixed points. There is also no clear connection between the halo virialized mass and these parameters. This implies that we still do not understand the origin of the profiles of dark matter structures.
We generate the peculiar velocity field for the 2MASS Redshift Survey (2MRS)
catalog using an orbit-reconstruction algorithm. The reconstructed velocities
of individual objects in 2MRS are well-correlated with the peculiar velocities
obtained from high-precision observed distances within 3,000 km/s. We estimate
the mean matter density to be 0.31 +/- 0.05 by comparing observed to
reconstructed velocities in this volume. The reconstructed motion of the Local
Group in the rest frame established by distances within 3,000 km/s agrees with
the observed motion and is generated by fluctuations within this volume, in
agreement with observations. Then, we reconstruct the velocity field of 2MRS in
successively larger radii, to study the problem of convergence towards the CMB
dipole. We find that less than half of the amplitude of the CMB dipole is
generated within a volume enclosing the Hydra-Centaurus-Norma supercluster at
around 40 Mpc/h. Although most of the amplitude of the CMB dipole seems to be
recovered by 120 Mpc/h, we observe no convergence up to this scale.
We develop a new statistical model which allows us to estimate cosmological
para meters from the reconstructed growth of convergence of the velocity of the
Local Group towards the CMB dipole motion. For scales up to 50 Mpc/h, assuming
a Local Group velocity of 627 km/s, we estimate Omega_m h^2 = 0.08 +/- 0.03 and
sigma_8=0.84 +/- 0.47, in agreement with WMAP5 measurements at the 1 to 2-sigma
level. However, for scales up to 100 Mpc/h, we obtain Omega_m h^2 = 0.05 +/-
0.02 and sigma_8=1.31 +/- 0.80, which agrees only at the 2 to 3-sigma level
with WMAP5 results. Weighing our likelihood analysis by the probability of
occurrence of the velocity of the Local Group does not change the
aforementioned disagreement. (abridged)
We investigate the old globular cluster (GC) population of 68 faint (Mv>-16 mag) dwarf galaxies located in the halo regions of nearby (<12 Mpc) loose galaxy groups and in the field environment based on archival HST/ACS images in F606W and F814W filters. The combined color distribution of 175 GC candidates peaks at (V-I)=0.96 +/- 0.07 mag and the GC luminosity function turnover for the entire sample is found at Mv,to = -7.6 +/- 0.11 mag, similar to the old metal-poor LMC GC population. Our data reveal a tentative trend of Mv,to becoming fainter from late-type to early-type galaxies. The luminosity and color distributions of GCs in dIrrs shows a lack of faint blue GCs. Our analysis reveals that this might reflect a relatively younger GC system than typically found in luminous early-type galaxies. If verified by spectroscopy this would suggest a later formation epoch of the first metal-poor star clusters in dwarf galaxies. We find several bright (massive) GCs which reside in the nuclear regions of their host galaxies. These nuclear clusters have similar luminosities and structural parameters as the peculiar Galactic clusters suspected of being the remnant nuclei of accreted dwarf galaxies, such as M54 and wCen. Except for these nuclear clusters, the distribution of GCs in dIrrs in the half-light radius vs. cluster mass plane is very similar to that of Galactic young halo clusters, which suggests comparable formation and dynamical evolution histories. A comparison with theoretical models of cluster disruption indicates that GCs in low-mass galaxies evolve dynamically as self-gravitating systems in a benign tidal environment.
We present a novel model in which shortening of a magnetic flux tube following localized, three-dimensional reconnection generates strong gas-dynamic shocks around its apex. The shortening releases magnetic energy by progressing away from the reconnection site at the Alfven speed. This launches inward flows along the field lines whose collision creates a pair of gas-dynamic shocks. The shocks raise both the mass density and temperature inside the newly shortened flux tube. Reconnecting field lines whose initial directions differ by more that 100 degrees can produce a concentrated knot of plasma hotter that 20 MK, consistent with observations. In spite of these high temperatures, the shocks convert less than 10% of the liberated magnetic energy into heat - the rest remains as kinetic energy of bulk motion. These gas-dynamic shocks arise only when the reconnection is impulsive and localized in all three dimensions; they are distinct from the slow magnetosonic shocks of the Petschek steady-state reconnection model.
We investigate the physical and chemical conditions necessary for low-mass star formation in extragalactic environments by calculating various characteristic timescales associated with star formation for a range of initial conditions. The balance of these timescales indicates whether low-mass star formation is enhanced or inhibited under certain physical conditions. In this study, we consider timescales for free-fall, cooling, freeze-out, desorption, chemistry and ambipolar diffusion and their variations with changes in the gas density, metallicity, cosmic ray ionisation rate and FUV radiation field strength. We find that extragalactic systems with high FUV radiation field strengths and high cosmic ray fluxes considered at a range of metallicities, are likely to have enhanced low-mass star formation unless the magnetic pressure is sufficient to halt collapse. Our results indicate that this is only likely to be the case for high-redshift galaxies approaching solar metallicities. Unless this is true for all high-redshift sources, this study finds little evidence for a high-mass biased IMF at high redshifts.
Diffuse 511 keV line emission, from the annihilation of cold positrons, has been observed in the direction of the Galactic Centre for more than 30 years. The latest high-resolution maps of this emission produced by the SPI instrument on INTEGRAL suggest at least one component of the emission is spatially coincident with the distribution of ~70 luminous, low-mass X-ray binaries detected in the soft gamma-ray band. The X-ray band, however, is generally a more sensitive probe of X-ray binary populations. Recent X-ray surveys of the Galactic Centre have discovered a much larger population (>4000) of faint, hard X-ray point sources. We investigate the possibility that the positrons observed in the direction of the Galactic Centre originate in pair-dominated jets generated by this population of fainter accretion-powered X-ray binaries. We also consider briefly whether such sources could account for unexplained diffuse emission associated with the Galactic Centre in the microwave (the WMAP `haze') and at other wavelengths. Finally, we point out several unresolved problems in associating Galactic Centre 511 keV emission with the brightest X-ray binaries.
Dark matter particles form halos that contribute the major part of the mass of galaxy clusters. The formation of these cosmological structures have been investigated both observationally and in numerical simulations, which have confirmed the existence of a universal mass profile. However, the dynamic behaviour of dark matter in halos is not as well understood. We have used observations of 16 equilibrated galaxy clusters to show that the random velocities of dark matter particles are larger on average along the radial direction than along the tangential, and that the magnitude of this velocity anisotropy is radially varying. Our measurement implies that the collective behaviour of dark matter particles is fundamentally different from that of normal particles and the radial variation of the anisotropy velocity agrees with the predictions of numerical simulation.
Radial velocity searches for extrasolar planets have discovered stars undergoing slow accelerations. The accelerations are likely due to one or more gas giant planets or brown dwarfs orbiting with period longer than the total time span of observations. The stellar acceleration is proportional to the mass of the companion divided by the square of its radius from the star. In this paper we predict the distribution of accelerations using a Monte Carlo method and assuming a semi-major axis and mass distribution for the companions. Radial velocity surveys find that ~20 and 10% of stars surveyed exhibit accelerations above ~10 and 25 m s^-1 yr^-1, respectively. We find that an extrapolation of the size and period distribution found by radial velocity surveys within ~ AU or companion imaging surveys predicts too few systems with detectable accelerations. The fractions of stars with accelerations above these values can be matched if every star hosts a gas giant planet or brown dwarf with semi-major axes between 4 and 20 AU or if a significant fraction (~70%) of stars host 3 or more massive planets in this range. This suggests that there is a large undiscovered population of gas giant planets and brown dwarfs present with semi-major axes in the 5 to 30 AU range.
An overview is given of multiwavelength observations of young supernova remnants, with a focus on the observational signatures of efficient cosmic ray acceleration. Some of the effects that may be attributed to efficient cosmic ray acceleration are the radial magnetic fields in young supernova remnants, magnetic field amplification as determined with X-ray imaging spectroscopy, evidence for large post-shock compression factors, and low plasma temperatures, as measured with high resolution optical/UV/X-ray spectroscopy. Special emphasis is given to spectroscopy of post-shock plasma's, which offers an opportunity to directly measure the post-shock temperature. In the presence of efficient cosmic ray acceleration the post-shock temperatures are expected to be lower than according to standard equations for a strong shock. For a number of supernova remnants this seems indeed to be the case.
The discovery of X-ray emission from cosmic sources in the 1960s has opened a
new powerful observing window on the Universe. In fact, the exploration of the
X-ray sky during the 70s-90s has established X-ray astronomy as a fundamental
field of astrophysics. Today, the emission from astrophysical sources is by
large best known at energies below 10 keV. The main reason for this situation
is purely technical since grazing incidence reflection has so far been limited
to the soft X-ray band. Above 10 keV all the observations have been obtained
with collimated detectors or coded mask instruments. To make a leap step
forward in X-ray astronomy above 10 keV it is necessary to extend the principle
of focusing X ray optics to higher energies, up to 80 keV and beyond. To this
end, ASI and CNES are presently studying the implementation of a X-ray mission
called Simbol-X.
Taking advantage of emerging technology in mirror manufacturing and
spacecraft formation flying, Simbol-X will push grazing incidence imaging up to
80 keV and beyond, providing a strong improvement both in sensitivity and
angular resolution compared to all instruments that have operated so far above
10 keV. This technological breakthrough will open a new high-energy window in
astrophysics and cosmology. Here we will address the problematic of the
development for such a distributed and deformable instrument. We will focus on
the main performances of the telescope, like angular resolution, sensitivity
and source localization. We will also describe the specificity of the
calibration aspects of the payload distributed over two satellites and
therefore in a not "frozen" configuration.
We derive the molecular properties for a sample of 301 Galactic HII regions including 123 ultra compact (UC), 105 compact, and 73 diffuse nebulae. We analyze all sources within the BU-FCRAO Galactic Ring Survey (GRS) of 13CO emission known to be HII regions based upon the presence of radio continuum and cm-wavelength radio recombination line emission. Unlike all previous large area coverage 13CO surveys, the GRS is fully sampled in angle and yet covers ~75 square degrees of the Inner Galaxy. The angular resolution of the GRS 46" allows us to associate molecular gas with HII regions without ambiguity and to investigate the physical properties of this molecular gas. We find clear CO/HII morphological associations in position and velocity for ~80% of the nebular sample. Compact HII region molecular gas clouds are on average larger than UC clouds: 2.2' compared to 1.7'. Compact and UC HII regions have very similar molecular properties, with ~5K line intensities and ~4 km/s line widths. The diffuse HII region molecular gas has lower line intensities, ~3K, and smaller line widths, ~3.5 km/s. These latter characteristics are similar to those found for quiescent molecular clouds in the GRS. Our sample nebulae thus show evidence for an evolutionary sequence wherein small, dense molecular gas clumps associated with UC HII regions grow into older compact nebulae and finally fragment and dissipate into large, diffuse nebulae.
In the present work we focus on future experiments using cluster abundance observations to constraint the Dark Energy equation of state parameter, w. To obtain tight constraints from this kind of experiment, a reliable sample of galaxy clusters must be obtained from deep and wide-field images. We therefore present the computational environment (2DPHOT) that allow us to build the galaxy catalog from the images and the Voronoi Tessellation cluster finding algorithm that we use to identify the galaxy clusters on those catalogs. To test our pipeline with data similar in quality to what will be gathered by future wide field surveys, we process images from the Deep fields obtained as part of the LEGACY Survey (four fields of one square degree each, in five bands, with depth up to r'=25). We test our cluster finder by determining the completeness and purity of the finder when applied to mock galaxy catalogs made for the Dark Energy Survey cluster finder comparison project by Risa Wechsler and Michael Busha. This procedure aims to understand the selection function of the underlying dark matter halos.
We present 'empirical' models (pressure vs. density) of Saturn's interior constrained by the gravitational coefficients J_2, J_4, and J_6 for different assumed rotation rates of the planet. The empirical pressure-density profile is interpreted in terms of a hydrogen and helium physical equation of state to deduce the hydrogen to helium ratio in Saturn and to constrain the depth dependence of helium and heavy element abundances. The planet's internal structure (pressure vs. density) and composition are found to be insensitive to the assumed rotation rate for periods between 10h:32m:35s and 10h:41m:35s. We find that helium is depleted in the upper envelope, while in the high pressure region (P >~ 1 Mbar) either the helium abundance or the concentration of heavier elements is significantly enhanced. Taking the ratio of hydrogen to helium in Saturn to be solar, we find that the maximum mass of heavy elements in Saturn's interior ranges from ~ 6 to 20 M_Earth. The empirical models of Saturn's interior yield a moment of inertia factor varying from 0.22271 to 0.22599 for rotation periods between 10h:32m:35s and 10h:41m:35s, respectively. A long-term precession rate of about 0.754" yr^{-1} is found to be consistent with the derived moment of inertia values and assumed rotation rates over the entire range of investigated rotation rates. This suggests that the long-term precession period of Saturn is somewhat shorter than the generally assumed value of 1.77 x 10^6 years inferred from modeling and observations.
We present preliminary results for a neutrino oscillation analysis in progress on data collected with the IceCube 22-string detector during 2007 and 2008. The goal of this analysis is to measure muon neutrino disappearance as a function of energy for a constant baseline length of the diameter of the Earth by studying vertically up-going muon neutrinos. At this baseline disappearance effects are expected to become sizable at neutrino energies below 100 GeV. This energy range has not been previously explored with IceCube, however due to IceCube's vertical geometry there is some sensitivity for this specific class of events. Based on preliminary selection criteria, we show that IceCube has the potential to detect these events and we estimate the sensitivity to determining oscillation parameters.
Using a sample of 21 damped Lyman alpha systems (DLAs) and 35 sub-DLAs, we evaluate the D-index = EW / Delta v x 1000 from high resolution spectra of the MgII lambda 2796 profile. This sample represents an increase in sub-DLA D-index statistics by a factor of four over the sample used by Ellison (2006). We investigate various techniques to define the velocity spread (Delta v) of the MgII line to determine an optimal D-index for the identification of DLAs. The success rate of DLA identification is 50 -- 55%, depending on the velocity limits used, improving by a few percent when the column density of FeII is included in the D-index calculation. We recommend the set of parameters that is judged to be most robust, have a combination of high DLA identification rate (57%) and low DLA miss rate (6%) and most cleanly separate the DLAs and sub-DLAs (Kolmogorov-Smirnov probability 0.5%). These statistics demonstrate that the D-index is the most efficient technique for selecting low redshift DLA candidates: 65% more efficient than selecting DLAs based on the equivalent widths of MgII and FeII alone. We also investigate the effect of resolution on determining the N(HI) of sub-DLAs. We convolve echelle spectra of sub-DLA Lya profiles with Gaussians typical of the spectral resolution of instruments on the Hubble Space Telescope and compare the best fit N(HI) values at both resolutions. We find that the fitted HI column density is systematically over-estimated by ~ 0.1 dex in the moderate resolution spectra compared to the best fits to the original echelle spectra. This offset is due to blending of nearby Lya clouds that are included in the damping wing fit at low resolution.
We present infrared interferometric observations of the inner regions of two A-star debris disks, beta Leo and zeta Lep, using the FLUOR instrument at the CHARA interferometer on both short (30 m) and long (>200 m) baselines. For the target stars, the short baseline visibilities are lower than expected for the stellar photosphere alone, while those of a check star, delta Leo, are not. We interpret this visibility offset of a few percent as a near-infrared excess arising from dust grains which, due to the instrumental field of view, must be located within several AU of the central star. For beta Leo, the near-infrared excess producing grains are spatially distinct from the dust which produces the previously known mid-infrared excess. For zeta Lep, the near-infrared excess may be spatially associated with the mid-infrared excess producing material. We present simple geometric models which are consistent with the near and mid-infrared excess and show that for both objects, the near-infrared producing material is most consistent with a thin ring of dust near the sublimation radius with typical grain sizes smaller than the nominal radiation pressure blowout radius. Finally, we discuss possible origins of the near-infrared emitting dust in the context of debris disk evolution models.
Jupiter was imaged during the Science Demonstration of the MCAO Demonstrator
(MAD) at the European Southern Observatory's UT3 Very Large Telescope unit. Io
and Europa were used as natural guide stars on either side of Jupiter,
separated from each other by about 1.6 arcmin from 23:41 to 01:32 UT (2008 Aug
16/17). The corrected angular resolution was 0.090 arcsec across the entire
field of view, as measured on background stars.
The observations at 2.02, 2.14, and 2.16 micrometers were sensitive to
portions of the Jovian spectrum with strong methane absorption. The data probe
the upper troposphere, which is populated with a fine (~0.5 micrometer) haze.
Two haze sources have been proposed: lofting of fine cloud particles into the
stable upper troposphere, and condensation of hydrazine produced via ammonia
photochemistry. The upper tropospheric haze is enhanced over Jupiter's
equatorial region.
Dramatic changes in the underlying cloud cover--part of the 2006/2007 "global
upheaval"--may be associated with changes in the equatorial haze distribution
now evident in the 2008 MAD images. Haze reflectivity peaked at 5 degrees N in
HST/NICMOS data from 2005, but it now peaks at the equator. The observations
suggest that haze variation is controlled by particle size, cloud source
variation, diffusion, and horizontal transport.
Our recently completed one billion particle Via Lactea II simulation of a Milky Way-sized dark matter halo resolves over 50,000 gravitationally bound clumps orbiting today within the virialized region of the main host. About 2,300 of these subhalos have one or more "progenitors" above 1e6 Msun at redshift 11, i.e. massive enough for their gas to have cooled via excitation of H2 and fragmented prior to the epoch of cosmic reionization. We count 4,500 such progenitors: if these were able to convert a fraction of their gas content into very metal-poor stars with a Salpeter initial mass function (IMF), they would be shining today with a visual magnitude M_V=6.7 per solar mass in stars. Assuming a universal baryon fraction, we show that mean star formation efficiencies as low as 0.1% in progenitors below 1e8 Msun would overproduce the abundance of the faint Galatic dwarf spheroidals observed by the Sloan Digital Sky Survey. Star formation at first light must have occurred either with an IMF lacking stars below 0.9 Msun, or was intrinsically very inefficient in small dark matter halos. If the latter, our results may be viewed as another hint of a minimum scale in galaxy formation.
We analyzed the regions of star formation in the spiral galaxies NGC 3184 and NGC 3938 from archive images at multiple wavelengths (NUV from GALEX, H-alpha from JKT and KPNO, 8 and 24 um from Spitzer, and CO from BIMA). We used the Clump Find Algorithm to extract the properties of the star forming tracers shown as emission regions at each wavelength. We obtained a power-law relation between the luminosity and the emission region volume that scales as expected, $L proportional to V, for the H-alpha and NUV emission; but much faster for the dust (8 and 24 um) and molecular gas emitting regions in CO. This is interpreted as a change on the emissivity with the size of the cloud, either by an augmentation of the overall density or due to the presence of high density clumps, with high local emissivity coefficients. Although the clumpy nature of molecular gas may not be surprising, the clumpy nature of mid-infrared emission regions, that could be explained by newly formed high to intermediate mass stars embedded into the dust and heating it, is clearly revealed in both galaxies.
Recently, stellar collapse involving black hole formation from massive stars is suggested to emit enormous fluxes of neutrinos on par with ordinary core-collapse supernovae. We investigate their detectability for the currently operating neutrino detector, SuperKamiokande. Neutrino oscillation is also taken into account for the evaluation. We find that the event number is larger than or comparable to that of supernova neutrinos and, hence, black hole formation is also a candidate for neutrino astronomy. Moreover, we find that the event number depends dominantly on the equation of state used in the computations of the black hole formation. This fact implies that the detection of neutrinos emitted from the black hole progenitors is very valuable to probe the properties of the equation of state for hot and/or dense matter.
We present the ASCA and Suzaku studies of the TeV source HESS J1837--069, which has not been identified in other wave-lengths. We confirm the presence of two X-ray sources in the Suzaku XIS image, AX J1838.0--0655 and AX J1837.3--0652, near both ends of the elongated TeV emission region. The XIS spectra of the two sources are reproduced by an absorbed power-law model, whose parameters are all consistent with those determined by the ASCA data. Recently, 70.5 ms X-ray pulsation has been detected with RXTE in the sky region including HESS J1837--069 (2008, ApJ, 681, 515). Using the ASCA GIS data which has both timing and imaging capabilities, we identified the pulsation source as AX J1838.0--0655. The pulse periods determined by ASCA and Suzaku, and that reported with RXTE indicate steady spin-down at $\dot{P} = 4.917(4) \times 10^{-14}$ s s$^{-1}$. These results suggest that AX J1838.0--0655 is an intrinsically stable source, and presumably a pulsar wind nebula (PWN). We discuss the possibility that AX J1838.0--0655 is associated with HESS J1837--069 and the VHE gamma-ray emission is originated from the PWN.
The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating successfully at Yangbajing in Tibet, China since 1999. Using the dataset collected by this array from 1999 November through 2005 November, we obtained the energy spectrum of $\gamma$-rays from the Crab Nebula, expressed by a power law as $(dJ/dE) = (2.09\pm0.32)\times10^{-12} (E/{\rm 3 TeV})^{-2.96\pm0.14} {\rm cm}^{-2} {\rm s}^{-1} {\rm TeV}^{-1}$ in the energy range of 1.7 to 40 TeV. This result is consistent with other independent $\gamma$-ray observations by imaging air Cherenkov telescopes. In this paper, we carefully checked and tuned the performance of the Tibet-III array using data on the moon's shadow in comparison with a detailed Monte Carlo simulation. The shadow is shifted to the west of the moon's apparent position as an effect of the geomagnetic field, although the extent of this displacement depends on the primary energy positively charged cosmic rays. This finding enables us to estimate the systematic error in determining the primary energy from its shower size. This error is estimated to be less than $\pm$12% in our experiment. This energy scale estimation is the first attempt among cosmic-ray experiments at ground level. The systematic pointing error is also estimated to be smaller than $0\fdg011$. The deficit rate and position of the moon's shadow are shown to be very stable within a statistical error of $\pm$6% year by year. This guarantees the long-term stability of point-like source observation with the Tibet-III array. These systematic errors are adequately taken into account in our study of the Crab Nebula.
We present new high spatial resolution VLT and VLA observations of a sample of nine low-power (P_{1.4 GHz} < 10^{25} W/Hz) radio hotspots. Infrared/optical emission is definitely detected in four of the nine observed objects, resulting in a detection rate of at least 45%. This emission is interpreted as synchrotron radiation from the electrons accelerated in the hot spots. The integrated spectra of these hotspots reveal typical break frequencies between 10^5 and 10^6 GHz, two orders of magnitude higher than typically found in high-power hotspots. This supports the idea that in low-power hotspots with their relatively low magnetic field strengths electrons emit most of their energy at higher frequencies. A simple spectral ageing analysis would imply that the emitting electrons have been injected into the hotspot volume less than ~10^3 years ago. We discuss possible scenarios to explain the lack of older electrons in the hotspot region. In particular, the extended morphology of the NIR/optical emission would suggest that efficient re-acceleration mechanisms rejuvenate the electron populations.
We discuss $\gamma$-ray emissions from the outer gap accelerators of middle-aged pulsars for part of the series of our studies. A two-dimensional electrodynamic model is used to solve the distribution of accelerating electric fields with electron and positron pair creation and radiation processes in the magnetic meridional plane. We compute the curvature radiation and the synchrotron radiation by solving the evolution of the Lorentz factor and the pitch angle. The calculated spectra are compared with observed phase-averaged spectra. We also use a three-dimensional geometrical model to discuss the pulse profiles. We argue that the outer gap of middle-aged pulsars occupies the whole region between the last-open field lines and the critical magnetic field lines, which are perpendicular to the rotational axis at the light cylinder. We assume that there is no outer gap accelerator inside the light cylinder between the rotational axis and the critical magnetic field lines. For the Geminga pulsar, we demonstrate that the outward curvature radiation dominates in the spectrum above 10 MeV, while the inward synchrotron radiation dominates below 10 MeV. We find that the computed spectrum is consistent with the observations in X-ray through $\gamma$-ray bands. With the pulse morphology of the $\gamma$-ray emissions, we argue that the inclination angle and the viewing angle for the Geminga pulsar are $\alpha\sim 50^{\circ}$ and $\xi\sim 90^{\circ}$, respectively.
The Seyfert 1.9 galaxy MCG-05-23-016 has been shown to exhibit a complex X-ray spectrum. This source has moderate X-ray luminosity, hosts a comparably low-mass black hole, but accretes at a high Eddington rate, and allows us to study a super massive black hole in an early stage. Three observations of the INTEGRAL satellite simultaneous with pointed Swift/XRT observations performed from December 2006 to June 2007 are used in combination with public data from the INTEGRAL archive to study the variability of the hard X-ray components and to generate a high-quality spectrum from 1 to 150 keV. The AGN shows little variability in the hard X-ray spectrum, with some indication of a variation in the high-energy cut-off energy ranging from 50 keV to >>100 keV, with an electron plasma temperature in the 10 - 90 keV range. The reflection component is not evident and, if present, the reflected fraction can be constrained to R < 0.3 for the combined data set. Comparison to previous observations shows that the reflection component has to be variable. No variability in the UV and optical range is observed on a time scale of 1.5 years. The hard X-ray spectrum of MCG-05-23-016 appears to be stable with the luminosity and underlying power law varying moderately and the optical/UV flux staying constant. The spectral energy distribution appears to be similar to that of Galactic black hole systems, e.g. XTE 1118+480 in the low state. The AGN exhibits a remarkably high Eddington ratio of L(bol)/L(Edd)> 0.8 (or L(bol)/L(Edd) > 0.1, if we consider a higher mass of the central engine) and, at the same time, a low cut-off energy around 70 keV. Objects like MCG-05-23-016 might indicate the early stages of super massive black holes, in which a strong accretion flow feeds the central engine.
We employ contemporaneous optical, UV and X-ray observations from the XMM-Newton EPIC-pn and Optical Monitor (OM) archives to present, for the first time, simultaneous spectral energy distributions (SEDs) for the majority of the Peterson et al. (2004) reverberation mapped sample of active galactic nuclei (AGN). The raw data were reduced using the latest pipelines and are all analysed consistently. The virial mass estimates from Peterson et al. (2004) allow us to calculate Eddington ratios lambda_Edd for the sample using the bolometric accretion luminosities determined directly from the SEDs. We calculate hard X-ray bolometric corrections kappa_2-10keV for the sample and confirm a trend for increasing bolometric correction with Eddington ratio proposed in previous studies. Our comparison with previous work on these objects suggests that the OM bandpass may be less susceptible to intrinsic reddening than the far-UV peak of the thermal disc spectrum in AGN, yielding larger bolometric corrections than previous work: kappa_2-10keV ~ 15 - 30 for lambda_Edd <~ 0.1, kappa_2-10keV ~ 20 - 70 for 0.1 <~ lambda_Edd <~ 0.2 and kappa_2-10keV ~ 70 - 150 for lambda_Edd >~ 0.2, but part of this increase could be attributed to spectral complexity preventing accurate recovery of the intrinsic luminosity in some sources. Long-term optical-UV variability contributes a second-order, but significant change to the total bolometric luminosity when comparing multiple observations for individual objects.We also consider the effect of a recently proposed correction for radiation pressure when determining black hole masses with reverberation mapping, and find that the revised mass estimates do not significantly alter the range of bolometric corrections seen but may yield a narrower distribution of Eddington ratios.
We present 26 point-sources discovered with Chandra within 200" (~20kpc) of the center of the barred supergiant galaxy NGC 1365. The majority of these sources are high-mass X-ray binaries, containing a neutron star or a black hole accreting from a luminous companion at a sub-Eddington rate. Using repeat Chandra and XMM-Newton as well as optical observations, we discuss in detail the natures of two highly-variable ultraluminous X-ray sources (ULXs): NGC 1365 X1, one of the most luminous ULXs known since the ROSAT era, which is X-ray variable by a factor of 30, and NGC 1365 X2, a newly discovered transient ULX, variable by a factor of >90. Their maximum X-ray luminosities (3-5 x 10^40 erg/s, measured with Chandra) and multiwavelength properties suggest the presence of more exotic objects and accretion modes: accretion onto intermediate mass black holes (IMBHs) and beamed/super-Eddington accretion onto solar-mass compact remnants. We argue that these two sources have black-hole masses higher than those of the typical primaries found in X-ray binaries in our Galaxy (which have masses of <20 Msolar), with a likely black-hole mass of 40-60 Msolar in the case of NGC 1365 X1 with a beamed/super-Eddington accretion mode, and a possible IMBH in the case of NGC 1365 X2 with M=80-500Msolar.
Aims: To determine Sigma (variation of Fe abundance with the optical depth), tau{FeI}, tau{FeII} (Rosseland median optical depth of Fe lines) and Delta[Fe/H](=[FeI/H]-[FeII/H]), in 79 Exoplanet Host stars (66 main sequence and 13 giants), with respect to 322 solar neighborhood field stars (9 main sequence and 313 giant stars). Methods: We derived FeI and FeII abundances using equivalent width measurements together with ATLAS9 (Kurucz 1993) model atmospheres and the WIDTH9 program. Results: The Rosseland median optical depths tau{FeI} and tau{FeII} are dependent on stellar parameters (log g, T{eff} and xi). We conclude that Sigma is a more reliable stratification indicator than tau{FeI}, tau{FeII} and Delta[Fe/H]. Our results show that statistically most EH stars (main sequence and giants) have an stratification similar to field stars, which is in agreement with the primordial hyphotesis of metal enhancement. The lack of correlation between Sigma and the exoplanet parameters (minimum mass, semiaxis and eccentricity) for most of the EH stars, and between [FeI/H] and Sigma, favors the primordial hypothesis of metal-enrichment. However, we cannot discard that some EH stars (and even non-EH stars) have suffered and accretion process in the past. We consider candidate stars with stratified atmospheres those with Sigma < 0: 20% (13/65) main sequence EH stars and 33% (4/12) giant EH stars. The group of candidate main sequence stars with stratified atmospheres (Sigma < 0), seems to show a correlation with [FeI/H], which probably relate the stratification in these stars with accretion events. Finally, our sample of 13 giant exoplanet host stars present solar metallicity values (median = -0.09 dex).
Evolution of self-gravitating rotating dense stellar systems (e.g. globular clusters, galactic nuclei) with embedded black holes is investigated. The interaction between the black hole and stellar component in differential rotating flattened systems is followed. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster rotation using 2D+1 Fokker Planck numerical methods. The models can reproduce the Bahcall-Wolf $f \propto E^{1/4}$ ($\rho \propto r^{-7/4}$) cusp inside the zone of influence of the black hole. Angular momentum transport and star accretion support the development of central rotation in relaxation time scales. Gravogyro and gravothermal instabilities conduce the system to a faster evolution leading to shorter collapse times with respect to the non-rotating systems. We explore system dissolution due to mass loss due to a galaxy tidal field (e.g. globular clusters).
The soft gamma-ray repeater (SGR) SGR 1900+14 lies a few arcminutes outside the edge of the shell supernova remnant (SNR) G42.8+0.6. A physical association between the two systems has been proposed - for this and other SGR-SNR pairs - based on the expectation of high space velocities for SGRs in the framework of the magnetar model. The large angular separation between the SGR and the SNR center, coupled with the young age of the system, suggest a test of the association with a proper motion measurement. We used a set of three Chandra/ACIS observations of the field spanning 5 years to perform accurate relative astrometry in order to measure the possible angular displacement of the SGR as a function of time. Our investigation sets a 3-sigma upper limit of 70 mas/yr to the overall proper motion of the SGR. Such a value argues against an association of SGR 1900+14 with G42.8+0.6 and adds further support to the mounting evidence for an origin of the SGR within a nearby, compact cluster of massive stars.
We present a model-independent method to test for scale-dependent non-Gaussianities in combination with scaling indices as test statistics. Therefore, surrogate data sets are generated, in which the power spectrum of the original data is preserved, while the higher order correlations are partly randomised by applying a scale-dependent shuffling procedure to the Fourier phases. We apply this method to the WMAP data of the cosmic microwave background (CMB) and find signatures for non-Gaussianities on large scales. Further tests are required to elucidate the origin of the detected anomalies.
The RAdial Velocity Experiment (RAVE) is an ambitious survey to measure the radial velocities, temperatures, surface gravities, metallicities and abundance ratios for up to a million stars using the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO), over the period 2003 - 2011. The survey represents a big advance in our understanding of our own Milky Way galaxy. The main data product will be a southern hemisphere survey of about a million stars. Their selection is based exclusively on their I--band colour, so avoiding any colour-induced bias. RAVE is expected to be the largest spectroscopic survey of the Solar neighbourhood in the coming decade, but with a significant fraction of giant stars reaching out to 10 kpc from the Sun. RAVE offers the first truly representative inventory of stellar radial velocities for all major components of the Galaxy. Here we present the first scientific results of this survey as well as its second data release which doubles the number of previously released radial velocities. For the first time, the release also provides atmospheric parameters for a large fraction of the second year data, making it an unprecedented tool to study the formation of the Milky Way. Plans for further data releases are outlined.
We studied the temperature and abundance distributions of intra-cluster medium (ICM) in the Abell 262 cluster of galaxies observed with Suzaku. Abell 262 is a bright, nearby poor cluster with ICM temperature of ~2 keV, thus providing useful information about the connection of ICM properties between groups and clusters of galaxies. The observed spectrum of the central region was well-represented by two temperature models, and the spectra for the outer regions were described by single temperature model. With the XIS instrument, we directly measured not only Si, S, and Fe lines but also O and Mg lines and obtained those abundances to an outer region of ~0.43 r_180 for the first time. We found steep gradients for Mg, Si, S, and Fe abundances, while O showed almost flat abundance distribution. Abundance ratios of alpha-elements to Fe were found to be similar to those of the other clusters and groups. We calculated the number ratio of type II to type Ia supernovae for the ICM enrichment to be 3.0 +- 0.6 within 0.1 r_180, and the value was consistent with those for other clusters and groups. We also calculated metal mass-to-light ratios (MLRs) for Fe, O and Mg (IMLR, OMLR, MMLR) with B-band and K-band luminosities of the member galaxies of Abell 262. The derived MLRs were comparable to those for other clusters with kT = 3-4 keV.
PAMELA is a space telescope orbiting around the Earth since June 2006. The scientific objectives addressed by the mission are the measurement of the antiprotons and positrons spectra in cosmic rays, the hunt for anti-nuclei as well as the determination of light nuclei fluxes from Hydrogen to Oxygen in a wide energy range and with very high statistics. In this paper the charge discrimination capabilities of the PAMELA Time-Of-Flight system for light nuclei, determined during a beam test calibration, will be presented.
Sun-like oscillations, that is p-modes excited stochastically by convective
noise, have now been observed in a number of Red Giant stars. Compared to those
seen in the Sun, these modes are of large amplitude and long period, making the
oscillations attractive prospects for observation. However, the low Q-factor of
these modes, and issues relating to the rising background at low frequencies,
present some interesting challenges for identifying modes and determining the
related asteroseismic parameters.
We report on the analysis procedure adopted for peak-bagging by our group at
Birmingham, and the techniques used to robustly ensure these are not a product
of noise. I also show results from a number of giants extracted from multi-year
observations with the SMEI instrument.
The discovery of an HI cloud with peculiar properties at equatorial coordinates (J2000) ra=07h49m, dec=04d30m is presented. The HI object was detected at 21cm using the 300-m NAIC Arecibo telescope. Subsequent follow-up high-resolution observations with the NRAO Very Large Array (VLA) telescope at L-Band revealed more details about its morphology. The most intriguing aspect of the object is the clear velocity gradient of 1 km/s, which is present in the data, an indication of either rotation or expansion. The gas appears to be cold, and its morphology is somewhat elliptical with clumpy substructure. Assuming disk rotation, the dynamical mass could be determined as a function of distance.Depending on the exact nature of the velocity gradient in the HI cloud, we can reach some preliminary conclusions about the nature of the object. Expansion would imply association with a circumstellar envelope of an evolved AGB star, while in the case of rotation, a comparison between the visible and the dynamical mass can lead to some preliminary conclusions. A common feature of those conclusions is the presence of a gravitational potential well, which is required to account for the rotation of the trapped HI gas. This potential well could be associated with a dark galaxy or some other exotic object.
The discovery of hypervelocity binary stars (HVBs) in the Galactic halo would provide definite evidence of the existence of a massive black hole companion to Sgr A*. Here we use an hybrid approach to compute the rate of ejection and the total number of HVBs produced by a hypothetical intermediate-mass black hole (IMBH, M_2<10^5\msun) orbiting Sgr A*. Depending on the mass of M_2 and on the properties of binary stars in the central parsec of the Milky Way, we show that the number of undisrupted HVBs expected to be expelled from the Galactic Center before binary black hole coalescence ranges from zero to a few dozens at most. Therefore, the non-detection of stellar binaries in a complete survey of hypervelocity stars would not rule out the occurrence of an IMBH-Sgr A* in-spiralling event within the last few 10^8 years.
We are developing automated systems to provide homogeneous calibration meta-data for heterogeneous imaging data, using the pixel content of the image alone where necessary. Standardized and complete calibration meta-data permit generative modeling: A good model of the sky through wavelength and time--that is, a model of the positions, motions, spectra, and variability of all stellar sources, plus an intensity map of all cosmological sources--could synthesize or generate any astronomical image ever taken at any time with any equipment in any configuration. We argue that the best-fit or highest likelihood model of the data is also the best possible astronomical catalog constructed from those data. A generative model or catalog of this form is the best possible platform for automated discovery, because it is capable of identifying informative failures of the model in new data at the pixel level, or as statistical anomalies in the joint distribution of residuals from many images. It is also, in some sense, an astronomer's "theory of everything".
In this paper we analyze nine SCUBA cores in Ophiuchus using the
second-lowest rotational transitions of four molecular species (12CO, 13CO,
C18O, and C17O) to search for clues to the evolutionary state and
star-formation activity within each core. Specifically, we look for evidence of
outflows, infall, and CO depletion. The line wings in the CO spectra are used
to detect outflows, spectral asymmetries in 13CO are used to determine infall
characteristics, and a comparison of the dust emission (from SCUBA
observations) and gas emission (from C18O) is used to determine the fractional
CO freeze-out.
Through comparison with Spitzer observations of protostellar sources in
Ophiuchus, we discuss the usefulness of CO and its isotopologues as the sole
indicators of the evolutionary state of each core. This study is an important
pilot project for the JCMT Legacy Survey of the Gould Belt (GBS) and the
Galactic Plane (JPS), which intend to complement the SCUBA-2 dust continuum
observations with HARP observations of 12CO, 13CO, C18O, and C17O J = 3 - 2 in
order to determine whether or not the cold dust clumps detected by SCUBA-2 are
protostellar or starless objects.
Our classification of the evolutionary state of the cores (based on molecular
line maps and SCUBA observations) is in agreement with the Spitzer designation
for six or seven of the nine SCUBA cores. However, several important caveats
exist in the interpretation of these results, many of which large mapping
surveys like the GBS may be able to overcome to provide a clearer picture of
activity in crowded fields.
Unresolved Doppler velocity measurements are not homogenous across the solar disc (Brookes et al. 1978). We consider one cause of the inhomogeneity that originates from the BiSON instrumentation itself: the intensity of light observed from a region on the solar disc is dependent on the distance between that region on the image of the solar disc formed in the instrument and the detector. The non-uniform weighting affects the realization of the solar noise and the amplitudes of the solar oscillations observed by a detector. An 'offset velocity', which varies with time, is observed in BiSON data and has consequences for the long-term stability of observations. We have attempted to model, in terms of the inhomogeneous weighting, the average observed offset velocity.
The UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) has the necessary combination of filters (Y, J, H and K), depth (Y <~ 20.2) and area coverage (~4000 deg^2) to detect several redshift z >~ 6.4 quasars. The Third Data Release (DR3) included ~1000 deg^2 of LAS observations which have so far yielded two previously known z ~= 6 quasars and two new discoveries: ULAS J0203+0012, at z = 5.72; and ULAS J1319+0950, at z = 6.13.
The Optical Monitoring Camera (OMC) on-board the INTEGRAL satellite has, as one of its scientific goals, the observation of a large number of variable sources previously selected. After almost 6 years of operations, OMC has monitored more than 100 000 sources of scientific interest. In this contribution we present the OMC Scientific Archive (this http URL) which has been developed to provide the astronomical community with a quick access to the light curves generated by this instrument.We describe the main characteristics of this archive, as well as important aspects for the users: object types, temporal sampling of light curves and photometric accuracy.
Gamma-ray Bursts (GRBs) are among the potential extragalactic sources of very-high-energy (VHE) gamma-rays. We discuss the prospects of detecting VHE gamma-rays with current ground-based Cherenkov instruments during the afterglow phase. Using the fireball model, we calculate the synchrotron self-Compton (SSC) emission from forward-shock electrons. The modeled results are compared with the observational afterglow data taken with and/or the sensitivity level of ground-based VHE instruments (e.g. STACEE, H.E.S.S., MAGIC, VERITAS, and Whipple). We find that modeled SSC emission from bright and nearby bursts such as GRB 030329 are detectable by these instruments even with a delayed observation time of ~10 hours.
Integrated spectroscopy is the method of choice for deriving the ages of unresolved stellar systems. However, hot stellar evolutionary stages, such as hot horizontal branch stars and blue straggler stars (BSSs), can affect the integrated ages measured using Balmer lines. Such hot, "non-canonical" stars may lead to overestimations of the temperature of the main sequence turn-off, and therefore underestimations of the integrated age of a stellar population. Using an optimized Hbeta index in conjunction with HST/WFPC2 color-magnitude diagrams (CMDs), we show that Galactic globular clusters exhibit a large scatter in their apparent "spectroscopic" ages, which does not correspond to that in their CMD-derived ages. We find for the first time that the specific frequency of BSSs, defined within the same aperture as the integrated spectra, shows a clear correspondence with Hbeta in the sense that, at fixed metallicity, higher BSS ratios lead to younger "apparent" spectroscopic ages. Thus, the specific frequency of BSSs in globular clusters sets a fundamental limit on the accuracy for which spectroscopic ages can be determined for globular clusters, and maybe for other stellar systems like galaxies. The observational implications of this result are discussed.
Very long wavelength universal gravitational waves cannot now produce in clusters of galaxies velocity dispersions greater than that which these systems would possess if they were expanding with the Universe, if the Universe is not younger than $10^{10}$ yr and Hubble's constant is not less than 50 km/sec/ Mpc. A diagram shows that actual velocity dispersions are significantly greater than this limit.
We have identified an X-ray transient (hereafter M15 X-3) in the globular
cluster M15 from an archival Chandra grating observation. M15 X-3 appears at an
X-ray luminosity of 6*10^{33} ergs/s with a spectrum consistent with an
absorbed power law of photon index 1.51+-0.14. The object is identifiable in
archival Chandra HRC-I observations with an X-ray luminosity of 2-6*10^{31}
ergs/s and apparently soft colors, suggesting a neutron star low-mass X-ray
binary in quiescence. We also observe it in outburst in a 2007 Chandra HRC-I
observation, and in archival 1994-1995 ROSAT HRI observations.
We identify a likely optical/UV counterpart with a (possibly transient) UV
excess from archival HST data, which suggests a main sequence companion. We
argue that M15 X-3's behavior is similar to that of the very faint X-ray
transients which have been observed in the Galactic Center. We discuss several
explanations for its very low X-ray luminosity, with the assumption that we
have detected its companion. M15 X-3's uniquely low extinction and
well-determined distance make it an excellent target for future studies.
We show that the measurements of 10 GeV atmospheric neutrinos by an upcoming array of densely packed phototubes buried deep inside the IceCube detector at the South Pole can be used to determine the neutrino mass hierarchy for values of sin^2(2theta13) close to the present bound, if the hierarchy is normal. These results are obtained for an exposure of 100 Mton years and systematic uncertainties up to 10%.
We adopt a covariant formalism to derive exact evolution equations for nonlinear perturbations, in a universe dominated by two scalar fields. These scalar fields are characterized by non-canonical kinetic terms and an arbitrary field space metric, a situation typically encountered in inflationary models inspired by string theory. We decompose the nonlinear scalar perturbations into adiabatic and entropy modes, generalizing the definition adopted in the linear theory, and we derive the corresponding exact evolution equations. We also obtain a nonlinear generalization of the curvature perturbation on uniform density hypersurfaces, showing that on large scales it is sourced only by the nonlinear version of the entropy perturbation. We then expand these equations to second order in the perturbations, using a coordinate based formalism. Our results are relatively compact and elegant and enable one to identify the new effects coming from the non-canonical structure of the scalar fields Lagrangian.
We consider reheating after inflation with a non-standard kinetic term. We show that the difference in the kinetic term in different Hubble patches inherited from the long-wavelength moduli inhomogeneities may generate a significant level of non-Gaussianity after inflation.
In the present work we investigate the cosmological implications of holographic dark energy density in the Gauss-Bonnet framework. By formulating independently the two cosmological scenarios, and by enforcing their simultaneous validity, we show that there is a correspondence between the holographic dark energy scenario in flat universe and the phantom dark energy model in the framework of Gauss-Bonnet theory with a potential. This correspondence leads consistently to an accelerating universe. However, in general one has not full freedom of constructing independently the two cosmological scenarios. Specific constraints must be imposed on the coupling with gravity and on the potential.
We re-examine the data taken by the neutrino detectors during the supernova SN1987A. It is found that the Kamiokande data, in addition to the well known burst at 7:35 hours UT, show another one at 7:54 hours, with seven pulses in 6.2 seconds. This second burst supports the idea that the duration of the collapse was much longer than a few seconds, as already suggested by the LSD detection at 2:56 hours the same day, i.e. four and a half hours earlier. The correlations between the gravitational wave detectors (Rome and Maryland) and the neutrino detectors are also revisited. It is shown that the g.w. detectors exhibit significant correlations with both the LSD and the Kamiokande detectors over periods of one-two hours that are centered, in both cases, at the LSD time.
Solar forcing on climate has been reported in several studies although the evidence so far remains inconclusive. Here, we analyze the stream flow of one of the largest rivers in the world, the Parana in southeastern South America. For the last century, we find a strong correlation with the sunspot number, in multidecadal time scales, and with larger solar activity corresponding to larger stream flow. The correlation coefficient is r=0.78, significant to a 99% level. In shorter time scales we find a strong correlation with El Nino. These results are a step toward flood prediction, which might have great social and economic impacts.
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We present a semi-analytical hydrodynamical model for the structure of reconfinement shocks formed in astrophysical relativistic jets interacting with external medium. We take into account exact conservation laws, both across the shock front and in the zone of the shocked matter, and exact angular relations. Our results confirm a good accuracy of the approximate formulae derived by Komissarov & Falle (1997). However, including the transverse pressure gradient in the shocked jet, we predict an absolute size of the shock to be about about twice larger. We calculate the efficiency of the kinetic energy dissipation in the shock and show a strong dependence on both the bulk Lorentz factor and opening angle of the jet.
We analyse models of inflation in which isocurvature perturbations present during inflation are converted into the primordial curvature perturbation during instant preheating. This can be due to an asymmetry between the fields present either during inflation or during preheating. We consider all the constraints that the model must satisfy in order to be theoretically valid and to satisfy observations. We show that the constraints are very tight in all of the models proposed and special initial conditions are required for the models to work. In the case where the symmetry is strongly broken during inflation the non-Gaussianity parameter f_NL is generally large and negative.
With several detections, the technique of gravitational microlensing has proven useful for studying planets that orbit stars at Galactic distances, and it can even be applied to detect planets in neighbouring galaxies. So far, planet detections by microlensing have been considered to result from a change in the bending of light and the resulting magnification caused by a planet around the foreground lens star. However, in complete analogy to the annual parallax effect caused by the revolution of the Earth around the Sun, the motion of the source star around the common barycentre with an orbiting planet can also lead to observable deviations in microlensing light curves that can provide evidence for the unseen companion. We discuss this effect in some detail and study the prospects of microlensing observations for revealing planets through this alternative detection channel. Given that small distances between lens and source star are favoured, and that the effect becomes nearly independent of the source distance, planets would remain detectable even if their host star is located outside the Milky Way with a sufficiently good photometry (exceeding present-day technology) being possible. From synthetic light curves arising from a Monte-Carlo simulation, we find that the chances for such detections are not overwhelming and appear practically limited to the most massive planets (at least with current observational set-ups), but they are large enough for leaving the possibility that one or the other signal has already been observed. However, it may remain undetermined whether the planet actually orbits the source star or rather the lens star, which leaves us with an ambiguity not only with respect to its location, but also to its properties.
We present the first results of our optical spectroscopy program aimed to provide redshifts and identifications for the X-ray sources in the Extended Chandra Deep Field South. A total of 339 sources were targeted using the IMACS spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT. We measured redshifts for 186 X-ray sources, including archival data and a literature search. We find that the AGN host galaxies have on average redder rest-frame optical colors than non-active galaxies, and that they live mostly in the "green valley". The dependence of the fraction of AGN that are obscured on both luminosity and redshift is confirmed at high significance and the observed AGN spatial density is compared with the expectations from existing luminosity functions. These AGN show a significant difference in the mid-IR to X-ray flux ratio for obscured and unobscured AGN, which can be explained by the effects of dust self-absorption on the former. This difference is larger for lower luminosity sources, which is consistent with the dust opening angle depending on AGN luminosity.
The treatment of dust attenuation is crucial in order to compare the predictions of galaxy formation models with multiwavelength observations. Most past studies have either used simple analytic prescriptions or else full radiative transfer (RT) calculations. Here, we couple star formation histories and morphologies predicted by the semi-analytic galaxy formation model MORGANA with RT calculations from the spectrophotometric and dust code GRASIL to create a library of galaxy SEDs from the UV/optical through the far Infrared, and compare the predictions of the RT calculations with analytic prescriptions. We consider a low and high redshift sample, as well as an additional library constructed with empirical, non-cosmological star formation histories and simple (pure bulge or disc) morphologies. Based on these libraries, we derive fitting formulae for the effective dust optical depth as a function of galaxy physical properties such as metallicity, gas mass, and radius. We show that such fitting formulae can predict the V-band optical depth with a scatter smaller than 0.4 dex for both the low and high redshift samples, but that there is a large galaxy-to-galaxy scatter in the shapes of attenuation curves, probably due to geometrical variations, which our simple recipe does not capture well. However, our new recipe provides a better approximation to the GRASIL results at optical wavelength than standard analytic prescriptions from the literature, particularly at high redshift.
In light of recent indications for a large population of obscured active galactic nuclei (AGNs), we revisit the mean radiation efficiency from accretion onto supermassive black holes (SMBHs), epsilon, applying a bayesian approach. We use the integrated comoving energy density emitted by AGNs and compare it to the mass density of local SMBHs. When considering only optically-selected unobscured AGNs, we derive log_10[epsilon]=-1.77+0.16-0.11 or epsilon=1.7+0.8-0.4%. Using the AGNs selected using hard X-rays, which include unabsorbed and Compton-thin absorbed AGNs, we find log_10[epsilon]=-1.20+0.15-0.10 or epsilon=6.4+2.6-1.3%. Using optically-selected AGNs, and correcting for the obscured population, we inferr log_10[epsilon]=-1.17+0.11-0.08 or epsilon=6.7+1.9-1.1%, which we consider our best estimate. We also repeat this calculation for intrinsically luminous AGNs (M_B<-23, quasars), comparing to the SMBH mass density in local elliptical galaxies, and find log_10[epsilon]=-1.27+0.15-0.11 or epsilon=5.4+2.2-1.2%. We discuss how our results can be used to estimate the mean spin of accreting SMBHs, both assuming the standard thin-disk model of accretion onto black holes and also comparing to more recent simulations. Our results can rule out maximally rotating SMBHs (<a>=0.998 Gm_bh/c^2) at the >=98% confidence level, as well as high rotation values (<a> >=0.9 Gm_bh/c^2) with >=92% confidence. Our preferred values of <a> are ~0.25-0.60 Gm_bh/c^2, although even these might be overestimated. Hence, we find that on average, SMBHs are not rapidly spinning during accretion. Finally, using an independent measurement of Eddington ratios, we estimate the SMBH e-folding time for the brightest AGNs (quasars) to be <tau> =100+151-60 Myr.
The Pierre Auger Observatory has been taking data on the highest energy cosmic rays for the equivalent of over a year of full detector aperture. Comments are presented on results published so far.
Rather than giving a complete overview on extragalactic Zone of Avoidance research, this paper will highlight some recent discoveries in the ZOA, such as new NIR to FIR observations (IRSF, Spitzer) of the most massive disk galaxy found to-date (HIZOA 0836-43), and deep multi-wavelength observations of a spiral galaxy WKK 6167 undergoing transformation while infalling along the Great Attractor Wall into the Norma cluster - reminiscent of similar incidences observed in two galaxies at higher redshifts (z ~ 0.2). While the recent systematic multi-wavelengths approaches to uncover the large-scale structure of galaxies across the ZOA have proven quite successful, in particular in the Great Attractor region, they lack the required depth to answer open questions with regard to our understanding of the dynamics in the Local Universe. The actual mass distribution is poorly understood and does not satisfactorily explain the observed peculiar velocity fields and the CMB dipole. We will present future HI survey strategies to be pursued with the South African SKA Pathfinder MeerKAT in the ZOA, that can - amongst others - resolve the long-standing Great Attractor/Shapley controversy, and determine at which distance range the cumulative peculiar motion of the Local Group flattens off and the Universe becomes homogeneous.
The Caltech-Jodrell Bank very long baseline interferometry (VLBI) Surveys give detailed 5 GHz VLBI images of several hundred milliarcsecond (mas) radio sources, and the full width at half-maximum angular sizes of the corresponding compact cores. Using the latter, I have constructed an angular-diameter/redshift diagram comprising 271 objects, which shows clearly the expected features of such a diagram, without redshift binning. Cosmological parameters are derived which are compatible with existing concensus values, particularly when the VLBI data are combined with recent Baryon Accoustic Oscillations observations; the figures are presented as indications of what might be expected of larger samples of similar data. The importance of beaming and relativistic motion towards the observer is stressed; a model of the latter indicates that the emitting material is close to the observer's line of sight and moving with a velocity which brings it close to the observer's rest frame. With respect to linear size, these objects compare well in variance with type Ia supernovae; the efficacy of the latter is improved by the brighter-slower and brighter-bluer correlations, and by the inverse-square law.
We propose a method for cosmographic measurements by combining gravitational lensing of the cosmic microwave background (CMB) with cosmic shear surveys. We cross-correlate the galaxy counts in the lens plane with two different source planes: the CMB at $z \sim 1100$ and galaxies at an intermediate redshift. The ratio of the galaxy count/CMB lensing cross-correlation to the galaxy count/galaxy lensing cross correlation is shown to be a purely geometric quantity, depending only on the distribution function of the source galaxies. By combining Planck, ADEPT and LSST the ratio can be measured to $\sim 4%$ accuracy, whereas a future polarization based experiment like CMBPOL can make a more precise ($\sim 1%$) measurement. For cosmological models where the curvature and the equation of state parameter are allowed to vary, the direction of degeneracy defined by the measurement of this ratio is different from that traced out by Baryon Acoustic Oscillation (BAO) measurements. Combining this method with the stacked cluster mass reconstruction cosmography technique as proposed by Hu, Holz and Vale (2007), the uncertainty in the ratio can be further reduced, improving the constraints on cosmological parameters. We also study the implications of the lensing-ratio measurement for early dark energy models, in context of the parameterization proposed by Doran and Robbers (2006). For models which are degenerate with respect to the CMB, we find both BAO and lensing-ratio measurements to be insensitive to the early component of the dark energy density.
ANTARES is the first undersea neutrino telescope. It is in its complete configuration since May 2008 at about 2.5 km below the sea surface close to Marseille. Data from 12 lines are being analyzed and are producing first results. Here we discuss first analysis results for 5 lines and 10 lines, and we also comment on the performance of the full detector. We show that the detector has capabilities for discriminating upgoing neutrino events from the much larger amount of downgoing atmospheric muons and that data and simulation are in good agreement. We then discuss the physics reach of the detector for what concerns point-like source and dark matter searches.
[Abridged] We exploit the clustering of massive galaxies to perform a high efficiency imaging search for gravitational lenses. Our dataset comprises 44 fields imaged by the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS), each of which is centered on a lens discovered by the Strong Lens ACS Survey (SLACS). We compare four different search methods: 1) automated detection with the HST Archive Galaxy-scale Gravitational Lens Survey (HAGGLeS) robot, 2) examining cutout images of bright galaxies (BGs) after subtraction of a smooth galaxy light distribution, 3) examining the unsubtracted BG cutouts, and 4) performing a full-frame visual inspection of the ACS images. We compute purity and completeness and consider investigator time for the four algorithms, using the main SLACS lenses as a testbed. The first and second algorithms perform the best. We present the four new lens systems discovered during this comprehensive search, as well as one other likely candidate. For each new lens we use the fundamental plane to estimate the lens velocity dispersion and predict, from the resulting lens geometry, the redshifts of the lensed sources. Two of these new systems are found in galaxy clusters, which include the SLACS lenses in the two respective fields. Overall we find that the enhanced lens abundance (30^{+24}_{-8} lenses/degree^2) is higher than expected for random fields (12^{+4}_{-2} lenses/degree^2 for the COSMOS survey). Additionally, we find that the gravitational lenses we detect are qualitatively different from those in the parent SLACS sample: this imaging survey is largely probing higher-redshift, and lower-mass, early-type galaxies.
We present trigonometric parallax observations of GD 362 obtained over seven epochs using the MDM 2.4m Hiltner Telescope. The existence of a dust disk around this possibly massive white dwarf makes it an interesting target for parallax observations. The measured parallax for GD 362 places it at a distance of 50.6 pc, which implies that its radius and mass are ~ 0.0106 Rsun and 0.71 Msun, respectively. GD 362 is not as massive as initially thought (1.2Msun). Our results are entirely consistent with the distance and mass estimates (52.2 pc and 0.73 Msun) by Zuckerman et al., who demonstrated that GD 362 has a helium dominated atmosphere. Dropping GD 362 from the list of massive white dwarfs, there are no white dwarfs with M > 0.9 Msun that are known to host circumstellar dust disks.
We present 1.4 to 2.5 um integral field spectroscopy of 16 stars in the Braid Nebula star formation region in Cygnus OB7. These data forms one aspect of a large-scale multi-wavelength survey aimed at determining an unbiased estimate of the number, mass distribution, and evolutionary state of the young stars within this one square degree area of the previously poorly studied Lynds 1003 molecular cloud. Our new spectroscopic data, when combined with 2MASS near-IR photometry, provide evidence of membership of many of these objects in the regions pre-main sequence population. We discuss both the characteristics of the young stars found in the region and the level of star forming activity present.
We present new Keck II NIRSPEC high-spectral resolution 2 um echelle observations of the young eruptive variable star V1647 Orionis. This star went into outburst in late 2003 and faded to its pre-outburst brightness after approximately 26 months. V1647 Orionis is the illuminating star of McNeil's Nebula and is located near M 78 in the Lynds 1630 dark cloud. Our spectra have a resolving power of approximately 18,000 and allow us to study in detail the weak absorption features present on the strong near-IR veiled continuum. An analysis of the echelle orders containing Mg I (2.1066 um) and Al I (2.1099 um), Br-gamma (2.1661 um), the Na I doublet (2.206 and 2.209 um), and the CO overtone bandhead (2.2935 um) gives us considerable information on the physical and geometric characteristics of the regions producing these spectral features. We find that, at high-spectral resolution, V1647 Orionis in quiescence resembles a significant number of FU Orionis type eruptive variables and does not appear similar to the quiescent EX Lupi variables observed. This correspondence is discussed and implications for the evolutionary state of the star are considered.
We present a pilot study of the stellar populations of 8 AGN hosts at z~1 and compare to (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the GOODS South field obtained with the laser guide star adaptive optics (LGSAO) system at Keck Observatory. We combine this K' data with B, V, i, and z imaging from the ACS on HST to give multi-color photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGN as inferred from their high X-ray luminosities (L_X > 10^42 ergs/s) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [OIII] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR SEDs of the strong Type II AGN indicate that they are excited to LIRG (Luminous InfraRed Galaxy) status via galactic starbursting, while the strong Type I AGN are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGN at z~1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are byproducts of this starbursting.
Monte Carlo simulation is one of the best tools to study the complex spectra of Compton-thick AGNs and to figure out the relation between their nuclear structures and X-ray spectra. We have simulated X-ray spectra of Compton-thick AGNs obscured by an accretion torus whose structure is characterized by a half-opening angle, an inclination angle of the torus relative to the observer, and a column density along the equatorial plane. We divided the simulated spectra into three components: one direct component, an absorbed reflection component and an unabsorbed reflection component. We then deduced the dependencies of these components on the parameters describing the structure of the torus. Our simulation results were applied to fit the wide-band spectrum of the Seyfert 2 galaxy Mrk 3 obtained by $Suzaku$. The spectral analysis indicates that we observe the nucleus along a line of sight intercepting the torus near its edge, and the column density along the equatorial plane was estimated to be ~10^24 cm^-2. Using this model, we can estimate the luminosities of both the direct emission and the emission irradiating the surrounding matter. This is useful to find the time variability and time lag between the direct and reflected light.
Signal from scintillation detectors in showers with energies 10**17-10**20eV has been analyzed. It was determined, that for core distances >=200m the time scale of a particle arrival time at the detector constitutes 40-5000ns and longer. Events with fine structure of the signal have been observed. The pulse consists of several peaks (for vertical showers) and a single pulse (for inclined showers). There are some anomalous events with two pulses wherein such a pulse shape is presented in two, three and more detectors. A period between these pulses makes 60-350ns.
In order to better determine the physical properties of hot, massive stars as a function of metallicity, we obtained very high SNR optical spectra of 26 O and early B stars in the Magellanic Clouds. These allow accurate modeling even in cases where the He I 4471 line has an equivalent width of only a few tens of mA. The spectra were modeled with FASTWIND, with good fits obtained for 18 stars; the remainder show signatures of being binaries. We include stars in common to recent studies to investigate possible systematic differences. The "automatic" FASTWIND modeling method of Mokiem and collaborators produced temperatures 1100 K hotter on the average, presumably due to the different emphasis given to various temperature-sensitive lines. More significant, however, is that the automatic method always produced some "best" answer, even for stars we identify as composite (binaries). The temperatures found by the TLUSTY/CMFGEN modeling of Bouret, Heap, and collaborators yielded temperatures 1000 K cooler than ours, on average. Significant outliers were due either to real differences in the data (some of the Bouret/Heap data were contaminated by moonlight continua) or the fact we could detect the HeI line needed to better constrain the temperature. Our new data agrees well with the effective temperature scale we presented previously. We confirm that the "Of" emission-lines do not track luminosity classes in the exact same manner as in Milky Way stars. We revisit the the issue of the "mass discrepancy", finding that some of the stars in our sample do have spectroscopic masses that are significantly smaller than those derived from stellar evolutionary models. We do not find that the size of the mass discrepancy is simply related to either effective temperature or surface gravity.
We report the serendipitous discovery of an "Einstein Ring" in the optical band from the Sloan Digital Sky Survey (SDSS) data and associated four images of a background source. The lens galaxy appears to be a nearby dwarf spheroid at a redshift of 0.0375$\pm$0.002. The lensed quasar is at a redshift of 0.6842$\pm$0.0014 and its multiple images are distributed almost 360$^{o}$ around the lens nearly along a ring of radius $\sim$6."0. Single component lens models require a mass of the galaxy of almost 10$^{12}$ M$_{\odot}$ within 6".0 from the lens center. With the available data we are unable to determine the exact positions, orientations and fluxes of the quasar and the galaxy, though there appears evidence for a double or multiple merging image of the quasar. We have also detected strong radio and X-ray emissions from this system. It is indicative that this ring system may be embedded in a group or cluster of galaxies. This unique ring, by virtue of the closeness of the lens galaxy, offers possible probe to some of the key issues like mass-to-light ratio of intrinsically faint galaxies, existence of large scale magnetic fields in elliptical galaxies etc.
Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number. Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxy, such as the cosmogenic isotopes 14C and 10Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene. A separate section is devoted to reconstructions of strong solar energetic particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed.
The heating of the solar chromosphere and corona is a long-standing puzzle in solar physics. Hinode observations show the ubiquitous presence of chromospheric anemone jets outside sunspots in active regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their velocity is 10 to 20 kilometers per second. These small jets have an inverted Y-shape, similar to the shape of x-ray anemone jets in the corona. These features imply that magnetic reconnection similar to that in the corona is occurring at a much smaller spatial scale throughout the chromosphere and suggest that the heating of the solar chromosphere and corona may be related to small-scale ubiquitous reconnection.
CCD UBVRI photometry is presented for type II SN 2004dj for about 1200 days, starting day 2 past discovery. The photometric behaviour is typical for SNe II-P, although some minor peculiarities are noticed. We compare the photometric data for the host cluster S96 before and after SN 2004dj outburst and do not find any significant changes.
Leading spiral arms are a rare phenomenon. We present here one of the very few convincing candidates of spiral arms opening counter-intuitively in the same direction as the galaxy disk is rotating. This detection in a luminous IR galaxy (LIRG) IRAS 18293-3134 is based on near infrared (NIR) adaptive optics imaging with the Very Large Telescope and long-slit NIR spectroscopy with the Anglo-Australian Telescope. We discuss the orientation of the galaxy based on imaging and derive rotation curves from both emission and absorption features in the spectrum. The galaxy is strongly star-forming and has a minor companion in a high-velocity encounter. The fact that the arms of IRAS 18293-3134 are not easily traceable from optical images suggests that larger samples of high-quality NIR imaging of interacting systems and LIRGs might uncover further cases of leading arms, placing constraints on spiral arm theories and retrograde encounters, and especially on the relationship between disk masses and dark matter halo masses.
The Tremaine-Weinberg method is a well-known model independent technique for measuring density wave pattern speeds in spiral galaxies. Here we show how it can be applied to the data cubes (maps of surface brightness and velocity) obtained in H-alpha emission using a Fabry-Perot spectrometer. One of the main difficulties, the discontinuity of the H-alpha emission, is resolved using the neighbouring stellar continuum delivered by the data cube. We argue from symmetry that the motions not associated with the density wave should cancel. We show that our pattern speeds are reasonable by computing corotation radii, and comparing them to measured bar lengths. Simulations including star forming gas also add credibility to our results. Nevertheless it will be necessary to compare them with results using the spectra of the stellar components to quantify any systematic deviations from valid pattern speed values.
We examine nucleosynthesis in the electron capture supernovae of progenitor AGB stars with an O-Ne-Mg core (with the initial stellar mass of 8.8 M_\odot). Thermodynamic trajectories for the first 810 ms after core bounce are taken from a recent state-of-the-art hydrodynamic simulation. The presented nucleosynthesis results are characterized by a number of distinct features that are not shared with those of other supernovae from the collapse of stars with iron core (with initial stellar masses of more than 10 M_\odot). First is the small amount of 56Ni (= 0.002-0.004 M_\odot) in the ejecta, which can be an explanation for observed properties of faint supernovae such as SNe 2008S and 1997D. In addition, the large Ni/Fe ratio is in reasonable agreement with the spectroscopic result of the Crab nebula (the relic of SN 1054). Second is the large production of 64Zn, 70Ge, light p-nuclei (74Se, 78Kr, 84Sr, and 92Mo), and in particular, 90Zr, which originates from the low Y_e (= 0.46-0.49, the number of electrons per nucleon) ejecta. We find, however, that only a 1-2% increase of the minimum Y_e moderates the overproduction of 90Zr. In contrast, the production of 64Zn is fairly robust against a small variation of Y_e. This provides the upper limit of the occurrence of this type of events to be about 30% of all core-collapse supernovae.
We have derived whole-sky CMB polarization maps from the WMAP 5 year polarization data, using the Harmonic Internal Linear Combination (HILC) method. Our HILC method incorporates spatial variability of linear weights in a natural way and yields continuous linear weights over the entire sky. To estimate the power spectrum of HILC maps, we have derived a unbiased quadratic estimator, which is similar to the WMAP team's cross power estimator, but in a more convenient form for HILC maps. From our CMB polarization map, we have obtained TE correlation and E mode power spectra without applying any mask. They are similar to the WMAP team's estimation and consistent with the WMAP best-fit $\Lambda$CDM model. Foreground reduction by HILC method is more effective for high resolution and low noise data. Hence, our HILC method will enable effective foreground reduction in polarization data from the Planck surveyor.
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.
We have paired the Second Data Release of the Large Area Survey of the UKIRT Infrared Deep Sky Survey with the Fifth Data Release of the Sloan Digital Sky Survey to identify ten cool white dwarf candidates, from their photometry and astrometry. Of these ten, one was previously known to be a very cool white dwarf. We have obtained optical spectroscopy for seven of the candidates using the GMOS-N spectrograph on Gemini North, and have confirmed all seven as white dwarfs. Our photometry and astrometry indicates that the remaining two objects are also white dwarfs. Model analysis of the photometry and available spectroscopy shows that the seven confirmed new white dwarfs, and the two new likely white dwarfs, have effective temperatures in the range Teff = 5400-6600 K. Our analysis of the previously known white dwarf confirms that it is cool, with Teff = 3800 K. The cooling age for this dwarf is 8.7 Gyr, while that of the nine ~6000 K white dwarfs is 1.8-3.6 Gyr. We are unable to determine the masses of the white dwarfs from the existing data, and therefore we cannot constrain the total ages of the white dwarfs. The large cooling age for the coolest white dwarf in the sample, combined with its low estimated tangential velocity, suggests that it is an old member of the thin disk, or a member of the thick disk of the Galaxy, with an age 10-11 Gyr. The warmer white dwarfs appear to have velocities typical of the thick disk or even halo; these may be very old remnants of low-mass stars, or they may be relatively young thin disk objects with unusually high space motion.
We address the question of whether numerical particle-in-cell (PIC) simulations and laboratory laser-plasma experiments can (or will be able to, in the near future) model realistic gamma-ray burst (GRB) shocks. For this, we compare the radiative cooling time, t_cool, of relativistic electrons in the shock magnetic fields to the microscopic dynamical time of collisionless relativistic shocks -- the inverse plasma frequency of protons, omega_pp^{-1}. We obtain that for t_cool*omega_pp^{-1}\lesssim ~few hundred, the electrons cool efficiently at or near the shock jump and are capable of emitiing away a large fraction of the shock energy. Such shocks are well-resolved in existing PIC simulations; therefore, the microscopic structure can be studied in detail. Since most of the emission in such shocks would be coming from the vicinity of the shock, the spectral power of the emitted radiation can be directly obtained from finite-length simulations and compared with observational data. Such radiative shocks correspond to the internal baryon-dominated GRB shocks for the conventional range of ejecta parameters. Fermi acceleration of electrons in such shocks is limited by electron cooling, hence the emitted spectrum should be lacking a non-thermal tail, whereas its peak likely falls in the multi-MeV range. Incidentally, the conditions in internal shocks are almost identical to those in laser-produced plasmas; thus, such GRB-like plasmas can be created and studied in laboratory experiments using the presently available Petawatt-scale laser facilities. An analysis of the external shocks shows that only the highly relativistic shocks, corresponding to the extremely early afterglow phase, can have efficient electron cooling in the shock transition. We emphasize the importance of radiative PIC simulations for further studies.
Phenomena currently attributed to Dark Matter (DM) and Dark Energy (DE) are merely a result of the interplay between gravitational energy density, caused by the contraction of space by matter, and space dilation, caused by the energy density of the Cosmological Microwave Background (CMB). This interplay causes inhomogeneous and anisotropic expansion, in and around galaxies, where as the expansion of the universe, when viewed globally, is homogeneous and isotropic. These contentions lead to a theoretical derivation of the gravitational central acceleration in and around galaxies, and the determination of g0, the central acceleration where falttening of Rotation Curves (RC) replaces Keplerian behavior. Our results, which fit the observed flattening of RCs, resemble the phenomenological Tully-Fisher and Millgrom MOND relations. However, our central acceleration, g0, depends on the CMB energy density at the time of formation of a galaxy and, as opposed to MOND, is not a universal constant.
The main goal of this paper is to prove that accreting very low-mass stars and brown dwarfs can be identified in IPHAS, a Halpha emission survey of the northern Milky Way.Full exploitation of the IPHAS database and a future extension of it in the southern hemisphere will be useful to identify very low-mass accreting objects near and far well-known star forming regions. We have used Virtual Observatory tools to cross-match the IPHAS catalogue with the 2MASS catalogue. We defined photometric criteria to identify Halpha emission sources with near-infrared colours similar to known young very low-mass stars and brown dwarfs. 4000 candidates were identified that met our criteria over an area of 1600 square degrees. We present low-resolution optical spectra of 113 candidates. Spectral types have been derived for the 33 candidates that have spectroscopically confirmed Halpha emission, negligible reddening and M spectral class. We have also measured Halpha emission and investigated the NaI doublet (818.3 nm, 819.5 nm) in these 33 objects. We confirm that 33 IPHAS candidates have strong Halpha indicative of disk accretion for their spectral type. 23 of them have spectral class M4 or later, of which 10 have classes in the range M5.5-M7.0 and thus could be very young brown dwarfs. Also many objects have weak NaI doublet, an indication of low surface gravity.We conclude that IPHAS provides a very valuable database to identify accreting very low-mass stars and brown dwarfs, and that Virtual Observatory tools provide an efficient method for identifying these objects over large areas of the sky. Based on our success rate of 23 Halpha emission objects with spectral type in the range M4-M7 out of 113 candidates with spectroscopic follow-up, we estimate that there could be hundreds of such objects in the full IPHAS survey.
If sterile neutrinos exist and form halos in galactic centers, they can give rise to observational consequences. In particular, the sterile neutrinos decay radiatively and heat up the gas in the protogalaxy to achieve hydrostatic equilibrium, and they provide the mass to form supermassive blackholes. A natural correlation between the blackhole mass and velocity dispersion thus arises $\log(M_{BH,f}/M_{\odot})=\alpha \log (\sigma /200 {\rm km s^{-1}})+ \beta$ with $\alpha \approx 4$ and $\beta \approx 8$.
The MOND limit is shown to follow from a requirement of space-time scale invariance of the equations of motion for nonrelativistic, purely gravitational systems; i.e., invariance of the equations of motion under (t,r) goes to (qt,qr) in the limit where a0 goes to infiity . It is suggested that this should replace the definition of the MOND limit based on the asymptotic behavior of a Newtonian-MOND interpolating function. In this way, the salient, deep-MOND results--asymptotically flat rotation curves, the mass-rotational-speed relation (baryonic Tully-Fisher relation), the Faber-Jackson relation, etc.--follow from a symmetry principle. For example, asymptotic flatness of rotation curves reflects the fact that radii change under scaling, while velocities do not. I then comment on the interpretation of the deep-MOND limit as one of "zero mass": Rest masses, whose presence obstructs scaling symmetry, become negligible compared to the "phantom", dynamical masses--those that some would attribute to dark matter. Unlike the former masses, the latter transform in a way that is consistent with the symmetry. Finally, I discuss the putative MOND-cosmology connection, in particular the possibility that MOND-especially the deep-MOND limit--is related to the asymptotic de Sitter geometry of our universe. I point out, in this connection, the possible relevance of a (classical) de Sitter-conformal-field-theory (dS/CFT) correspondence.
A comparison of the correlation lengths of red galaxies with blue can provide a new cosmic ruler. Using 269,000 galaxies from the SDSS DR6 survey, I show that the 3D correlation length averaged over many clusters remains very nearly constant at Lo=4.797+/-0.024 Mpc/h from small redshifts out to redshifts of 0.5. This serves as a new measure of cosmic length scales as well as a means of testing the standard cosmological model that is almost free of selection biases. The cluster number density also appears to remain constant over this redshift range.
This paper continues previous work on the effects of turbulence on mean motion resonances in extrasolar planetary systems. Turbulence is expected to arise in the disks that form planets, and these fluctuations act to compromise resonant configurations. This paper extends previous work by considering how interactions between the planets and possible damping effects imposed by the disk affect the outcomes. These physical processes are studied using three approaches: numerical integrations of the 3-body problem with additional forcing due to turbulence, model equations that reduce the problem to stochastically driven oscillators, and Fokker-Planck equations that describe the time evolution of an ensemble of systems. With this combined approach, we elucidate the physics of how turbulence can remove extrasolar planetary systems from mean motion resonance. As expected, systems with sufficiently large damping (dissipation) can maintain resonance, in spite of turbulent forcing. In the absence of strong damping, ensembles of these systems exhibit two regimes of behavior, where the fraction of the bound states decreases as a power-law or as an exponential. Both types of behavior can be understood through the model developed herein. For systems with weak interactions between planets, the model reduces to a stochastic pendulum, and the fraction of bound states decreases as a power-law. For highly interactive systems, the dynamics are more complicated and the fraction of bound states decreases exponentially. We show how planetary interactions lead to drift terms in the Fokker-Planck equation and account for this exponential behavior. In addition to clarifying the physical processes involved, this paper strengthens the finding that turbulence implies that mean motions resonances should be rare.
Nonthermal X-rays and very high-energy (VHE) $\gamma$-rays have been detected from the supernova remnant (SNR) RX J1713.7-3946, and especially the recent observations with the \textit{Suzaku} satellite clearly reveal a spectral cutoff in the X-ray spectrum, which directly relates to the cutoff of the energy spectrum of the parent electrons. However, whether the origin of the VHE $\gamma$-rays from the SNR is hadronic or leptonic is still in debate. We studied the multi-band nonthermal emission from RX J1713.7-3946 based on a semi-analytical approach to the nonlinear shock acceleration process by including the contribution of the accelerated electrons to the nonthermal radiation. The results show that the multi-band observations on RX J1713.7-3946 can be well explained in the model with appropriate parameters and the TeV $\gamma$-rays have hadronic origin, i.e., they are produced via proton-proton (p-p) interactions as the relativistic protons accelerated at the shock collide with the ambient matter.
The determination of atmospheric parameters is the first and most fundamental step in the analysis of a stellar spectrum. Current and forthcoming surveys involve samples of up to several million stars, and therefore fully automated approaches are required to handle not just data reduction but also the analysis, and in particular the determination of atmospheric parameters. We propose that a successful methodology needs, at the very least, to pass a series of consistency tests that we dub the 'four-step program'. This and related issues are discussed in some detail in the context of the massive data set to be obtained with the Radial Velocity Spectrometer onboard Gaia
We combine spectroscopic metallicity values with integrated narrowband continuum colors to explore the internal metallicity distribution in early-type galaxies. The different techniques for determining metallicity (indices versus colors) allows for an estimate of the contribution from metal-poor stars in a predominantly metal-rich population which, in turn, places constraints on the shape and width of a galaxy's metallicity distribution function (MDF). The color-spectroscopic data is compared to the closed box, infall and inhomogeneous chemical evolution models. The G-dwarf problem, a deficiency in metal-poor stars as compared to closed box models, is evident in the dataset and indicates this deficiency is common to all early-type galaxies. However, even simple infall models predict galaxy colors which are too blue compared to the observations. A simple analytic model is proposed which matches the elliptical data and recent HST observations of M31 (Worthey et al 2005) and NGC 5128 (Harris & Harris 2000) by reducing the number of metal-poor stars in a systematic fashion. While without physical justification, the shape of these models are similar to predictions of inhomogeneous enrichment scenarios.
We present new constraints on the rapidly oscillating Ap star alpha Cir,
derived from a combination of interferometric and photometric data obtained
with the Sydney University Stellar Interferometer (SUSI) and the WIRE
satellite. The highlights of our study are:
1. The first determination of the angular diameter of an roAp star.
2. A nearly model-independent determination of the effective temperature of
alpha Cir, which is found to be lower than previously estimated values.
3. Detection of two new oscillation frequencies allowing a determination of
the large separation of alpha Cir.
Based on this new information, we have computed non-magnetic and magnetic
models for alpha Cir. We show that the value of the observed large separation
found from the new data agrees well with that derived from theoretical models.
Moreover, we also show how the magnetic field may explain some of the anomalies
seen in the oscillation spectrum and how these in turn provide constraints on
the magnitude and topology of the magnetic field.
A variety of intriguing polarization patterns are created when polarization observations of the single pulses from radio pulsars are displayed in a two-dimensional projection of the Poincare sphere. In many pulsars, the projections produce two clusters of data points that reside at antipodal points on the sphere. The clusters are formed by fluctuations in polarization amplitude that are parallel to the unit vectors representing the polarization states of the wave propagation modes in the pulsar magnetosphere. In other pulsars, however, the patterns are more complex, resembling annuli and bow ties or bars. The formation of these complex patterns is not understood and largely unexplored. An empirical model of pulsar polarization is used to show that these patterns arise from polarization fluctuations that are perpendicular to the mode vectors. The model also shows that the modulation index of the polarization amplitude is an indicator of polarization pattern complexity. A stochastic version of generalized Faraday rotation can cause the orientation of the polarization vectors to fluctuate and is a possible candidate for the perpendicular fluctuations incorporated in the model. Alternative models indicate that one mode experiences perpendicular fluctuations and the other does not, suggesting that the fluctuations could also be due to a mode-selective random process, such as scattering in the magnetosphere. A polarization stability analysis of the patterns implies that processes intrinsic to the emission are more effective in depolarizing the emission than fluctuations in the orientation of its polarization vector.
This work is a comprehensive investigation of the Yang-Mills condensate (YMC) dark energy (DE) model, which is extended to include the 3-loop quantum corrections. We study its cosmic evolution and the possibility of crossing phantom divide $w=-1$, examine in details the Hubble parameter $H$, the deceleration parameter $q$, the statefinder diagnosis $(r,s)$, and the $w-w^\prime$ diagnosis of the model without and with interaction, and compare our results with other DE models. Besides, by using the observational data of type Ia supernovae (SNIa), the shift parameter from cosmic microwave background (CMB), and the baryon acoustic oscillation (BAO) peak from large scale structures (LSS), we give the cosmological constraints on 3-loop YMC model. It is found that the model can naturally solve the coincidence problem, and its prediction of the afore-mentioned parameter is much closer to the $\Lambda$CDM model than other dynamics DE models; the introduction of the matter-DE interaction will make the YMC model deviating from the $\Lambda$CDM model, and will give an equation of state (EOF) crossing -1. Moreover, it is also found that, to fit the latest SNIa data alone, the $\Lambda$CDM model is slightly better than the 3-loop YMC model; but in fitting of the combination of SNIa, CMB and LSS data, the 3-loop YMC model performs better than the $\Lambda$CDM model.
A non-universal scalar mass supergravity type of model is explored where the first two generation of scalars and the third generation of sleptons may be very massive. Lighter or vanishing third generation of squarks as well as Higgs scalars at the unification scale cause the radiative electroweak symmetry breaking constraint to be less prohibitive. Thus, both FCNC/CP-violation problems as well as the naturalness problem are within control. We identify a large slepton mass effect in the RGE of $m_{H_D}^2$ (for the down type of Higgs) that may turn the later negative at the electroweak scale even for a small $\tan\beta$. A hyperbolic branch/focus point like effect is found for $m_A^2$ that may result in very light Higgs spectra. The lightest stable particle is dominantly a bino that pair annihilates via Higgs exchange, giving rise to a WMAP satisfied relic density region for all $\tan\beta$. Detection prospects of such LSPs in the upcoming dark matter experiments both of direct and indirect types (photon flux) are interesting. The Higgs bosons and the third generation of squarks are light in this scenario and these may be easily probed besides charginos and neutralinos in the early runs of LHC.
The interaction between a gravitational wave (GW) and entangled photons in the Walborn's "which-way experiment" on a double-slit quantum eraser is investigated. GWs change the polarization states in an entangled pair introducing decoherence and changing the experimental condition of the double slit quantum eraser. By varying the path of one of the entangled photons one can tune the GW detector to a certain specific wavelength, obtaining, in principle, the profile of the GW spectrum. The presence of GWs can be revealed by searching for entangled photon coincidences in the dark fringes of the recovered interference pattern of the quantum eraser, with the key advantage of discriminating the dark noise counts from the real counts due to photons deviated by the GW with heralded photon techniques. Alternatively, the incomplete destruction of the interference patterns may reveal the interaction of GWs with the photon's polarization. We propose this gedankenexperiment as an improvement to the already existing detection techniques in GW interferometers such as VIRGO, LIGO and future LISA by using heralded photons when enough bright entangled sources will be available.
This paper considers galactic scale Beacons from the point of view of expense to a builder on Earth. For fixed power density in the far field, what is the cost-optimum interstellar Beacon system? Experience shows an optimum tradeoff, depending on transmission frequency and on antenna size and power. This emerges by minimizing the cost of producing a desired effective isotropic radiated power, which in turn determines the maximum range of detectability of a transmitted signal. We derive general relations for cost-optimal aperture and power. For linear dependence of capital cost on transmitter power and antenna area, minimum capital cost occurs when the cost is equally divided between antenna gain and radiated power. For non-linear power law dependence a similar simple division occurs. This is validated in cost data for many systems; industry uses this cost optimum as a rule-of-thumb. Costs of pulsed cost-efficient transmitters are estimated from these relations using current cost parameters ($/W, $/m2) as a basis. Galactic-scale Beacons demand effective isotropic radiated power >1017 W, emitted powers are >1 GW, with antenna areas > km2. We show the scaling and give examples of such Beacons. Thrifty beacon systems would be large and costly, have narrow searchlight beams and short dwell times when the Beacon would be seen by an alien oberver at target areas in the sky. They may revisit an area infrequently and will likely transmit at higher microwave frequencies, ~10 GHz. The natural corridor to broadcast is along the galactic spiral radius or along the spiral galactic arm we are in. Our second paper argues that nearly all SETI searches to date had little chance of seeing such Beacons.
What would SETI Beacon transmitters be like if built by civilizations with a
variety of motivations, but who cared about cost? High-power transmitters might
be built for wide variety of motives other than two-way communication; Beacons
built to be seen over thousands of light years are such. Altruistic Beacon
builders will have to contend with other altruistic causes, just as humans do,
so may select for economy of effort. Cost, spectral lines near 1 GHz and
interstellar scintillation favor radiating frequencies substantially above the
classic water hole. Therefore the transmission strategy for a distant,
cost-conscious Beacon will be a rapid scan of the galactic plane, to cover the
angular space. Such pulses will be infrequent events for the receiver. Such
Beacons built by distant advanced, wealthy societies will have very different
characteristics from what SETI researchers seek. Future searches should pay
special attention to areas along the galactic disk where SETI searches have
seen coherent signals that have not recurred on the limited listening time
intervals we have used. We will need to wait for recurring events that may
arrive in intermittent bursts. Several new SETI strategies emerge from these
ideas.
Key words: SETI, METI, microwave, power beaming, beacons, radio astronomy,
array antennas, HPM
Links to: arXiv, form interface, find, astro-ph, recent, 0810, contact, help (Access key information)
Models that reproduce the observed high-velocity clouds (HVCs) also predict clouds at lower radial velocities that may easily be confused with Galactic disk (|z| < 1 kpc) gas. We describe the first search for these low-velocity halo clouds (LVHCs) using IRAS data and the initial data from the Galactic Arecibo L-band Feed Array survey in HI (GALFA-HI). The technique is based upon the expectation that such clouds should, like HVCs, have very limited infrared thermal dust emission as compared to their HI column density. We describe our 'displacement-map' technique for robustly determining the dust-to-gas ratio of clouds and the associated errors that takes into account the significant scatter in the infrared flux from the Galactic disk gas. We find that there exist lower-velocity clouds that have extremely low dust-to-gas ratios, consistent with being in the Galactic halo - candidate LVHCs. We also confirm the lack of dust in many HVCs with the notable exception of complex M, which we consider to be the first detection of warm dust in HVCs. We do not confirm the previously reported detection of dust in complex C. In addition, we find that most Intermediate- and Low-Velocity clouds that are part of the Galactic disk have a higher 60 micron/100 micron flux ratio than is typically seen in Galactic HI, which is consistent with a previously proposed picture in which fast-moving Galactic clouds have smaller, hotter dust grains.
Stars form in embedded star clusters which play a key role in determining the properties of a galaxy's stellar population. Physical mechanisms discussed in this paper are runaway stars shot out from young clusters, binary-star disruption in clusters, gas blow-out from clusters and the origin of thick galactic disks. I emphasise that the SNIa rate per low-mass star depends on the star-clusters formed in a galaxy and I discuss the IGIMF theory. Based on the IGIMF theory, the re-calibrated Halpha-luminosity--SFR relation implies dwarf irregular galaxies to have the same gas-depletion time-scale as major disk galaxies, suggesting a major change in our understanding of dwarf-galaxy evolution. The IGIMF-theory also naturally leads to the observed radial Halpha cutoff in disk galaxies without a radial star-formation cutoff. It emerges that the thorough understanding of the physics and distribution of star clusters may be leading to a major paradigm shift in our understanding of galaxy evolution.
Using a homogenous sample of 38,208 quasars with a sky coverage of $4000 {\rm deg^2}$ drawn from the SDSS Data Release Five quasar catalog, we study the dependence of quasar clustering on luminosity, virial black hole mass, quasar color, and radio loudness. At $z<2.5$, quasar clustering depends weakly on luminosity and virial black hole mass, with typical uncertainty levels $\sim 10%$ for the measured correlation lengths. These weak dependences are consistent with models in which substantial scatter between quasar luminosity, virial black hole mass and the host dark matter halo mass has diluted any clustering difference, where halo mass is assumed to be the relevant quantity that best correlates with clustering strength. However, the most luminous and most massive quasars are more strongly clustered (at the $\sim 2\sigma$ level) than the remainder of the sample, which we attribute to the rapid increase of the bias factor at the high-mass end of host halos. We do not observe a strong dependence of clustering strength on quasar colors within our sample. On the other hand, radio-loud quasars are more strongly clustered than are radio-quiet quasars matched in redshift and optical luminosity (or virial black hole mass), consistent with local observations of radio galaxies and radio-loud type 2 AGN. Thus radio-loud quasars reside in more massive and denser environments in the biased halo clustering picture. Using the Sheth et al.(2001) formula for the linear halo bias, the estimated host halo mass for radio-loud quasars is $\sim 10^{13} h^{-1}M_\odot$, compared to $\sim 2\times 10^{12} h^{-1}M_\odot$ for radio-quiet quasar hosts at $z\sim 1.5$.
We have constructed the first all-sky CMB temperature and polarization lensed maps based on a high-resolution cosmological N-body simulation, the Millennium Simulation (MS). We have exploited the lensing potential map obtained using a map-making procedure (Carbone et al. 2008) which integrates along the line-of-sight the MS dark matter distribution by stacking and randomizing the simulation boxes up to $z = 127$, and which semi-analytically supplies the large-scale power in the angular lensing potential that is not correctly sampled by the N-body simulation. The lensed sky has been obtained by properly modifying the LensPix code (Lewis 2005) to account for the MS structures. We have also produced all-sky lensed maps of the so-called $\psi_E$ and $\psi_B$ potentials, which are directly related to the electric and magnetic types of polarization. The angular power spectra of the simulated lensed temperature and polarization maps agree well with semi-analytic estimates up to $l < 2500$, while on smaller scales we find a slight excess of power which we interpret as being due to non-linear clustering in the MS. We also observe how non-linear lensing power in the polarised CMB is transferred to large angular scales by suitably misaligned modes in the CMB and the lensing potential. This work is relevant in view of the future CMB probes, as a way to analyse the lensed sky and disentangle the contribution from primordial gravitational waves.
We describe a phenomenological model for molecular hydrogen formation suited for applications in galaxy formation simulations, which includes on-equilibrium formation of molecular hydrogen on dust and approximate treatment of both its self-shielding and shielding by dust from the dissociating UV radiation. The model is applicable in simulations in which individual star forming regions - the giant molecular complexes - can be identified (resolution of tens of pc) and their mean internal density estimated reliably, even if internal structure is not resolved. In agreement with previous studies, calculations based on our model show that the transition from atomic to fully molecular phase depends primarily on the metallicity, which we assume is directly related to the dust abundance, and clumpiness of the interstellar medium. The clumpiness simply boosts the formation rate of molecular hydrogen, while dust serves both as a catalyst of molecular hydrogen formation and as an additional shielding from dissociating UV radiation. The upshot is that it is difficult to form fully-shielded giant molecular clouds while gas metallicity is low. However, once the gas is enriched to Z ~ 0.01-0.1 solar, the subsequent star formation and enrichment can proceed at a much faster rate. This may keep star formation efficiency in the low-mass, low-metallicity progenitors of galaxies very low for a certain period of time with the effect similar to a strong "feedback" mechanism. [abridged]
We show that measures of star formation rates (SFRs) for infrared galaxies using either single-band 24 um or extinction-corrected Paschen-alpha luminosities are consistent in the total infrared luminosity = L(TIR) ~ 10^10 L_sun range. MIPS 24 micron photometry can yield star formation rates accurately from this luminosity upward: SFR(M_sun/yr) = 7.8 x 10^-10 L(24 um, L_sun) from L(TIR) = 5 x 10^9 L_sun to 10^11 L_sun, and SFR = 7.8 x 10^-10 L(24 um, L_sun) x (7.76 x 10^-11 L(24))^0.048 for higher L(TIR). For galaxies with L(TIR) >= 10^10 L_sun, these new expressions should provide SFRs to within 0.2 dex. For L(TIR) >= 10^11 L_sun, we find that the SFR of infrared galaxies is significantly underestimated using extinction-corrected Pa-alpha (and presumably using any other optical or near infrared recombination lines). As a part of this work, we constructed spectral energy distribution (SED) templates for eleven luminous and ultraluminous purely star forming infrared galaxies (LIRGs and ULIRGs) and over the spectral range 0.4 microns to 30 cm. We use these templates and the SINGS data to construct average templates from 5 microns to 30 cm for infrared galaxies with L(TIR) = 5 x 10^9 to 10^13 L_sun. All of these templates are made available on line.
Axisymmetric magnetohydrodynamic (MHD) simulations have been applied to investigate the interrelation of a central stellar magnetosphere and stellar wind with a surrounding magnetized disk outflow and how the overall formation of a large scale jet is affected. The initial magnetic field distribution applied is a superposition of two components - a stellar dipole and a surrounding disk magnetic field, in both either parallel or anti-parallel alignment. Correspondingly, the mass outflow is launched as stellar wind plus a disk wind. Our simulations evolve from an initial state in hydrostatic equilibrium and an initially force-free magnetic field configuration. Due to initial differential rotation and induction of a strong toroidal magnetic field the stellar dipolar field inflates and is disrupted on large scale. Stellar and disk wind may evolve in a pair of collimated outflows. The existence of a reasonably strong disk wind component is essential for collimation. A disk jet as known from previous numerical studies will become de-collimated by the stellar wind. In some simulations we observe the generation of strong flares triggering a sudden change in the outflow mass loss rate by a factor of two and also a re-distribution in the radial profile of momentum flux and jet velocity across the jet. We discuss the hypothesis that these flares may trigger internal shocks in the asymptotic jets which are observed as knots.
I use high resolution N-body/SPH simulations to model the new proper motion of the Large Magellanic Cloud (LMC) within the Milky Way (MW) halo and investigate the effects of gravitational and hydrodynamical forces on the formation of the Magellanic Stream (MS). Both the LMC and the MW are fully self consistent galaxy models embedded in extended cuspy LCDM dark matter halos. I find that ram-pressure from a low density ionized halo is sufficient to remove a large amount of gas from the LMC's disk forming a trailing Stream that extends more than 120 degrees from the Cloud. Tidal forces elongate the satellite's disk but do not affect its vertical structure. No stars become unbound showing that tidal stripping is almost effectiveless.
For several hours on 2008 April 19 the T Tauri spectroscopic binary DQ Tau was observed to brighten, reaching a maximum detected flux of 468 mJy and likely making it (briefly) the brightest object at 3 mm in the Taurus star-forming region. We present the light curve of a rarely before observed millimeter flare originating in the region around a pre-main-sequence star, and the first from a classical T Tauri star. We discuss the properties and nature of the flaring behavior in the context of pulsed accretion flows (the current picture based largely on studies of this object's optically variable spectrum), as well as magnetospheric re-connection models (a separate theory that predicts millimeter flares for close binaries of high orbital eccentricity). We believe that the flare mechanism is linked to the binary orbit, and therefore periodic. DQ Tau makes a strong case for multi-wavelength follow-up studies, performed in parallel, of future flares to help determine whether magnetospheric and dynamical interactions in a proto-binary system are independent.
In this review we address the progress that has been made toward the understanding the population of Magellanic Cloud planetary nebulae since the last Magellanic Cloud Symposium. Planetary nebulae in the Clouds are not only important as key probes of stellar and ISM evolution in these galaxies, but also reflect the evolution of AGB stars and beyond in low-metallicity environments. We present the recent surveys results, including the wide fields ground-based search for PNe, the {\it HST} study of the resolves ejecta and their central stars, and the {\it Spitzer} analysis of the gas contents of these ejecta. Finally, we show how Magellanic Cloud PNe can be used to constraint the distance scale of galactic PNe.
The weak lensing power spectrum carries cosmological information via its dependence on the growth of structure and on geometric factors. Since much of the cosmological information comes from scales affected by nonlinear clustering, measurements of the lensing power spectrum can be degraded by non-Gaussian covariances. Recently there have been conflicting studies about the level of this degradation. We use the halo model to estimate it and include new contributions related to the finite size of lensing surveys, following Rimes and Hamilton's study of 3D simulations. We find that non-Gaussian correlations between different multipoles can degrade the cumulative signal-to-noise for the power spectrum amplitude by up to a factor of 2 (or 5 for a worst-case model that exceeds current N-body simulation predictions). However, using an eight-parameter Fisher analysis we find that the marginalized errors on individual parameters are degraded by less than 10% (or 20% for the worst-case model). The smaller degradation in parameter accuracy is primarily because: individual parameters in a high-dimensional parameter space are degraded much less than the volume of the full Fisher ellipsoid; lensing involves projections along the line of sight, which reduce the non-Gaussian effect; some of the cosmological information comes from geometric factors which are not degraded at all. We contrast our findings with those of Lee & Pen (2008) who suggested a much larger degradation in information content. Finally, our results give a useful guide for exploring survey design by giving the cosmological information returns for varying survey area, depth and the level of some systematic errors.
Optical and near-infrared (NIR) spectra are presented for ULAS
J131911.29+095951.4 (hereafter ULAS J1319+0950), a new redshift z = 6.127 +/-
0.004 quasar discovered in the Third Data Release (DR3) of the UKIRT Infrared
Deep Sky Survey (UKIDSS). The source has Y_Vega = 19.10 +/- 0.03, corresponding
to M_1450,AB = -27.12, which is comparable to the absolute magnitudes of the z
~= 6 quasars discovered in the SDSS. ULAS J1319+0950 was, in fact, registered
by SDSS as a faint source with z_AB = 20.1 +/- 0.1, just below the
signal-to-noise ratio limit of the main SDSS quasar survey. The faint z-band
magnitude is a consequence of the weak Ly alpha/N V emission line, which has a
rest-frame equivalent width of only ~20 A and provides only a small boost to
the z-band flux. Nevertheless, there is no evidence from this UKIDSS-based
search for a significant population of high-redshift quasars with weak emission
lines. The Ly alpha optical depth to ULAS J1319+0950 is consistent with that
measured towards similarly distant SDSS quasars, implying that results from
optical- and NIR-selected quasars can be combined.
Also presented is a new NIR-spectrum of the previously discovered UKIDSS
quasar ULAS J020332.38+001229.2, which reveals the object to be a broad
absorption line quasar. The new spectrum shows that the emission line
previously identified as Ly alpha is actually N V, leading to a revised
redshift of z = 5.72, rather than z = 5.86 as previously estimated.
We attempt to measure the proper motions of two magnetars - the soft gamma-ray repeater SGR 1900+14 and the anomalous X-ray pulsar 1E 2259+586 - using two epochs of Chandra observations separated by ~5 yr. We perform extensive tests using these data, archival data, and simulations to verify the accuracy of our measurements and understand their limitations. We find 90% upper limits on the proper motions of 54 mas/yr (SGR 1900+14) and 65 mas/yr (1E 2259+586), with the limits largely determined by the accuracy with which we could register the two epochs of data and by the inherent uncertainties on two-point proper motions. We translate the proper motions limits into limits on the transverse velocity using distances, and find v_perp < 1300 km/s (SGR 1900+14, for a distance of 5 kpc) and v_perp < 930 km/s (1E 2259+586, for a distance of 3 kpc) at 90% confidence; the range of possible distances for these objects makes a wide range of velocities possible, but it seems that the magnetars do not have uniformly high space velocities of > 3000 km/s. Unfortunately, our proper motions also cannot significantly constrain the previously proposed origins of these objects in nearby supernova remnants or star clusters, limited as much by our ignorance of ages as by our proper motions.
We demonstrate how interactive, three-dimensional (3-d) scientific
visualizations can be efficiently interchanged between a variety of mediums.
Through the use of an appropriate interchange format, and a unified interaction
interface, we minimize the effort to produce visualizations appropriate for
undertaking knowledge discovery at the astronomer's desktop, as part of
conference presentations, in digital publications or as Web content. We use
examples from cosmological visualization to address some of the issues of
interchange, and to describe our approach to adapting S2PLOT desktop
visualizations to the Web.
Supporting demonstrations are available at
this http URL
We present a method for measuring electrical currents enclosed by flux rope structures that are ejected within solar coronal mass ejections (CMEs). Such currents are responsible for providing the Lorentz self-force that propels CMEs. Our estimates for the driving current are based on measurements of the propelling force obtained using data from the LASCO coronagraphs aboard the SOHO satellite. We find that upper limits on the currents enclosed by CMEs are typically around $10^{10}$ Amperes. We estimate that the magnetic flux enclosed by the CMEs in the LASCO field of view is a few $\times 10^{21}$ Mx.
We investigate the properties of the Galactic ISM by applying Faraday tomography to a radio polarization data set in the direction of the Galactic anti-centre. We address the problem of missing large-scale structure in our data, and show that this does not play an important role for the results we present. The main peak of the Faraday depth spectra in our data set is not measurably resolved for about 8% of the lines of sight. An unresolved peak indicates a separation between the regions with Faraday rotation and synchrotron emission. However, cosmic rays pervade the ISM, and synchrotron emission would therefore also be produced where there is Faraday rotation. We suggest that the orientation of the magnetic field can separate the two effects. By modelling the thermal electron contribution to the Faraday depth, we map the strength of the magnetic field component along the line of sight. Polarized point sources in our data set have rotation measures that are comparable to the Faraday depths of the diffuse emission in our data. Our Faraday depth maps show narrow canals of low polarized intensity. We conclude that depolarization over the telescope beam produces at least some of these canals. Finally, we investigate the properties of one conspicuous region in this data set and argue that it is created by a decrease in line-of-sight depolarization compared to its surroundings.
We test the relation between relative f-mode frequency variation and Lagrangian perturbation in the solar radius obtained by Dziembowski and Goode (2004) using several pairs of solar models and show that it doesn't hold true for any of the model pairs we have used. We attempt to derive a better approximation for the kernel linking the relative frequency changes and the solar radius variation in the subsurface layers
We derive analytical solutions and dispersion relations of global magnetic Poincar\'e (magneto-gravity) and magnetic Rossby waves in the approximation of shallow water magnetohydrodynamics. The solutions are obtained in a rotating spherical coordinate system for strongly and weakly stable stratification separately in the presence of toroidal magnetic field. In both cases magnetic Rossby waves split into fast and slow magnetic Rossby modes. In the case of strongly stable stratification (valid in the radiative part of the tachocline) all waves are slightly affected by the layer thickness and the toroidal magnetic field, while in the case of weakly stable stratification (valid in the upper overshoot layer of the tachocline) magnetic Poincar\'e and fast magnetic Rossby waves are found to be concentrated near the solar equator, leading to equatorially trapped waves. However, slow magnetic Rossby waves tend to concentrate near the poles, leading to polar trapped waves. The frequencies of all waves are smaller in the upper weakly stable stratification region than in the lower strongly stable stratification one.
Modern spectroscopic databases provide a wealth of information about the
physical processes and environments associated with astrophysical populations.
Techniques such as blind source separation (BSS), in which sets of spectra are
decomposed into a number of components, offer the prospect of identifying the
signatures of the underlying physical emission processes. Principle Component
Analysis (PCA) has been applied with some success but is severely limited by
the inherent orthogonality restriction that the components must satisfy.
Non-negative matrix factorisation (NMF) is a relatively new BSS technique
that incorporates a non-negativity constraint on its components. In this
respect, the resulting components may more closely reflect the physical
emission signatures than is the case using PCA. We discuss some of the
considerations that must be made when applying NMF and, through its application
to the quasar spectra in the Sloan Digital Sky Survey (SDSS) DR6, we show that
NMF is a fast method for generating compact and accurate reconstructions of the
spectra.
The ability to reconstruct spectra accurately has numerous astrophysical
applications. Combined with improved SDSS redshifts, we apply NMF to the
problem of defining robust continua for quasars that exhibit strong broad
absorption line (BAL) systems. The resulting catalogue of SDSS DR6 BAL quasars
will be the largest available. Importantly, the NMF approach allows
quantitative error estimates to be derived for the Balnicity Indices as a
function of key astrophysical and observational parameters, such as the quasar
redshifts and the signal-to-noise ratio of the spectra.
Spain appears in light pollution maps as a country less polluted than their neighbours in the European Union. This seems to be an illusion due to its low population density. The data indicate that Spain is one of the most contaminated countries. To reach these conclusions we compare the Spanish case to those of other European countries.
We examine the angular momentum loss and associated rotational spindown for magnetic hot stars with a line-driven stellar wind and a rotation-aligned dipole magnetic field. Our analysis here is based on our previous 2-D numerical MHD simulation study that examines the interplay among wind, field, and rotation as a function of two dimensionless parameters, one characterizing the wind magnetic confinement ($\eta_{\ast} \equiv B_{eq}^{2} R_{\ast}^{2}/{\dot M} v_{\infty}$), and the other the ratio ($W \equiv V_{rot}/V_{orb}$) of stellar rotation to critical (orbital) speed. We compare and contrast the 2-D, time variable angular momentum loss of this dipole model of a hot-star wind with the classical 1-D steady-state analysis by Weber and Davis (WD), who used an idealized monopole field to model the angular momentum loss in the solar wind. Despite the differences, we find that the total angular momentum loss ${\dot J}$ averaged over both solid angle and time follows closely the general WD scaling ${\dot J} = (2/3) {\dot M} \Omega R_{A}^{2}$, where ${\dot M}$ is the mass loss rate, $\Omega$ is the stellar angular velocity, and $R_{A}$ is a characteristic Alfv\'{e}n radius. However, a key distinction here is that for a dipole field, this Alfv\'{e}n radius has a strong-field scaling $R_{A}/R_{\ast} \approx \eta_{\ast}^{1/4}$, instead of the scaling $R_{A}/R_{\ast} \sim \sqrt{\eta_{\ast}}$ for a monopole field. This leads to a slower stellar spindown time that in the dipole case scales as $\tau_{spin} = \tau_{mass} 1.5k/\sqrt{\eta_{\ast}}$, where $\tau_{mass} \equiv M/{\dot M}$ is the characteristic mass loss time, and $k$ is the dimensionless factor for stellar moment of inertia. The full numerical scaling relation we cite gives typical spindown times of order 1 Myr for several known magnetic massive stars.
In cosmic shear likelihood analyses the covariance is most commonly assumed to be constant in parameter space. Therefore, when calculating the covariance matrix (analytically or from simulations), its underlying cosmology should not influence the likelihood contours. We examine whether the aforementioned assumption holds and quantify how strong cosmic shear covariances vary within a reasonable parameter range. Furthermore, we examine the impact on likelihood contours when assuming different cosmologies in the covariance. We find that covariances vary significantly within the considered parameter range (Omega_m=[0.2;0.4], sigma_8=[0.6;1.0]) and that this has a non-negligible impact on the size of likelihood contours. This impact increases with increasing survey size, increasing number density of source galaxies, decreasing ellipticity noise, and when using non-Gaussian covariances. To improve on the assumption of a constant covariance we present two methods. The adaptive covariance is the most accurate method, but it is computationally expensive. To reduce the computational costs we give a scaling relation for covariances. As a second method we outline the concept of an iterative likelihood analysis. Here, we additionally account for non-Gaussianity using a ray-tracing covariance derived from the Millennium simulation.
We present radio-to-optical data taken by the WEBT, supplemented by VLBA and RXTE observations, of 3C 279. Our goal is to use this extensive database to draw inferences regarding the physics of the relativistic jet. We assemble multifrequency light curves with data from 30 ground-based observatories and the space-based instruments, along with linear polarization vs. time in the optical R band. In addition, we present a sequence of 22 images (with polarization vectors) at 43 GHz at resolution 0.15 milliarcsec, obtained with the VLBA. We analyse the light curves and polarization, as well as the spectral energy distributions at different epochs, corresponding to different brightness states. The IR-optical-UV continuum spectrum of the variable component corresponds to a power law with a constant slope of -1.6, while in the 2.4-10 keV X-ray band it varies in slope from -1.1 to -1.6. The steepest X-ray spectrum occurs at a flux minimum. During a decline in flux from maximum in late 2006, the optical and 43 GHz core polarization vectors rotate by ~300 degrees. The continuum spectrum agrees with steady injection of relativistic electrons with a power-law energy distribution of slope -3.2 that is steepened to -4.2 at high energies by radiative losses. The X-ray emission at flux minimum comes most likely from a new component that starts in an upstream section of the jet where inverse Compton scattering of seed photons from outside the jet is important. The rotation of the polarization vector implies that the jet contains a helical magnetic field that extends ~20 pc past the 43 GHz core.
We present preliminary calculations of electron scattering polarizations from models of structured cool star envelopes. We note that net polarizations from unresolved sources can result from non-spherical scattering envelopes and/or anisotropic illumination from a photosphere that has brightness variations. The resultant polarizations are quite small (hundreths of a percent); however, Rayleigh scattering from molecular opacity and/or dust scattering from the more extended envelope under similar considerations may produce higher polarizations.
Clusters of galaxies are the largest gravitationally bound objects in the Universe, containing about 10^15 solar masses of hot (10^8 K) gas, galaxies and dark matter in a typical volume of about 10 Mpc^3. Magnetic fields and relativistic particles are mixed with the gas as revealed by giant radio haloes, which arise from diffuse, megaparsec-scale synchrotron radiation at cluster center. Radio haloes require that the emitting electrons are accelerated in situ (by turbulence), or are injected (as secondary particles) by proton collisions into the intergalactic medium. They are found only in a fraction of massive clusters that have complex dynamics, which suggests a connection between these mechanisms and cluster mergers. Here we report a radio halo at low frequencies associated with the merging cluster Abell 521. This halo has an extremely steep radio spectrum, which implies a high frequency cut-off; this makes the halo difficult to detect with observations at 1.4 GHz (the frequency at which all other known radio haloes have been best studied). The spectrum of the halo is inconsistent with a secondary origin of the relativistic electrons, but instead supports turbulent acceleration, which suggests that many radio haloes in the Universe should emit mainly at low frequencies.
Two problems are discussed here. The first one is the 0.4 dex discrepancy between the 7Li abundance derived from the spectra of metal-poor halo stars on the one hand, and from Big Bang nucleosynthesis, based on the cosmological parameters constrained by the WMAP measurements, on the other hand. Lithium, indeed, can be depleted in the convection zone of unevolved stars. The understanding of the hydrodynamics of the crucial zone near the bottom of the convective envelope in dwarfs or turn-off stars of solar metallicity has recently made enormous progress with the inclusion of internal gravity waves. However, similar work for metal-poor stars is still lacking. Therefore it is not yet clear whether the depletion occurring in the metal-poor stars themselves is adequate to produce a 7Li plateau. The second problem pertains to the large amount of 6Li recently found in metal-poor halo stars. The convection-related asymmetry of the 7Li line could mimic the signal attributed so far to the weak blend of 6Li in the red wing of the 7Li line. Theoretical computations show that the signal generated by the asymmetry of 7Li is 2.0, 2.1, and 3.7 per cent for [Fe/H]= -3.0, -2.0, -1.0, respectively (Teff =6250 K and log g=4.0 [cgs]). In addition we re-investigate the statistical properties of the 6Li plateau and show that previous analyses were biased. Our conclusion is that the 6Li plateau can be reinterpreted in terms of intrinsic line asymmetry, without the need to invoke a contribution of 6Li. (abridged)
The study of Galactic diffuse $\gamma$ radiation combined with the knowledge of the distribution of the molecular hydrogen in the Galaxy offers a unique tool to probe the cosmic ray flux in the Galaxy. A methodology to study the level of the cosmic ray "sea" and to unveil target-accelerator systems in the Galaxy, which makes use of the data from the high resolution survey of the Galactic molecular clouds performed with the NANTEN telescope and of the data from gamma-ray instruments, has been developed. Some predictions concerning the level of the cosmic ray "sea" and the $\gamma$-ray emission close to cosmic ray sources for instruments such as Fermi and Cherenkov Telescope Array are presented.
We discuss the gravitational waves (GW) in the context of vector inflation. We derive the action for tensor perturbations and find that tachyonic instabilities are present in most (but not all) of the inflationary models with large fields. In contrast, the stability of the small field inflation ($A_{\mu}A^{\mu}\ll\frac{1}{N}$) is ensured by the usual slow-roll conditions, where $N$ is the total number of fields. For example, the Coleman-Weinberg potential and the power-law inflation are always stable in the small fields limit with an approximately flat spectrum of GW. We also provide some examples which lead to a rapid decay of GW and predict the absence of tensor modes in the CMB.
We demonstrate that the 1D cylindrical version of the Grad-Shafranov equation is more rich than classical self-similar ones, and more suitable for the astrophysical jets we observe. In particular, it allows us to describe the central (and, hence, the most energetic) part of the flow. Both relativistic and non-relativistic versions are discussed. It is shown that taking into account the finite pressure of the external media one can determine the magnetic flux within the central core. We found as well that for non-relativistic flows which are magnetically dominated near the origin the solution can be constructed only in the presense the oblique shock near the base of a jet where the additional heating is to take place.
We model the cosmic medium as the mixture of a generalized Chaplygin gas and a pressureless matter component. Within a neo-Newtonian approach (in which, different from standard Newtonian cosmology, the pressure enters the homogeneous and isotropic background dynamics) we compute the matter power spectrum. The 2dFGRS data are used to discriminate between unified models of the dark sector (a purely baryonic matter component of roughly 5 percent of the total energy content and roughly 95 percent generalized Chaplygin gas) and different models, for which there is separate dark matter, in addition to that accounted for by the generalized Chaplygin gas. Leaving the corresponding density parameters free, we find that the unified models are strongly disfavored. On the other hand, using unified model priors, the observational data are also well described, in particular for small and large values of the generalized Chaplygin gas parameter $\alpha$. The latter result is in agreement with a recent, more qualitative but fully relativistic, perturbation analysis in Gorini et al.
Magnification and de-magnification due to gravitational lensing will contribute to the brightness scatter of Type Ia supernovae (SNe Ia). The purpose of this paper is to investigate the possibility to decrease this scatter by correcting individual SNe Ia using observations of galaxies in the foreground, without introducing any extra bias. We simulate a large number of SN Ia lines of sight populated by galaxies. For each line of sight the true magnification factor and an estimate thereof are calculated. The estimated magnification factor corresponds to what an observer would infer from a survey like SNLS. Using the simulated data we investigate the possibility to estimate the magnification of individual supernovae with enough precision to be able to correct their brightness for gravitational lensing with negligible bias. Our simulations show that the bias arising from gravitational lensing corrections of individual SNe Ia is negligible for current and next generation surveys and that the scatter from lensing can be reduced by approximately a factor 2. The total scatter in the SN Ia magnitudes could be reduced by 4% for an intrinsic dispersion of 0.13 mag. For an intrinsic dispersion of 0.09 mag, which might not be to unrealistic for future surveys, the total scatter could be reduced by 6%. This will reduce the errors on cosmological parameters derived from supernova data by 4-8%. The prospect of correcting for lensing is thus very good.
We employ Coleman-Weinberg and Higgs potentials to implement inflation in non-supersymmetric grand unified theories (GUTs) such as SU(5) and SO(10). To realize a scalar spectral index close to 0.96, as indicated by the most recent WMAP 5-year anlaysis, the energy scale of observable inflation turns out to be of order $10^{16}$ GeV. This implies a GUT symmetry breaking scale of similar magnitude, and proton lifetime of order $10^{34}$-$10^{38}$ years. In some SO(10) models with axion dark matter, the scalar leptoquark boson exchange leads to proton decay with a lifetime of order $10^{34}$-$10^{35}$ years.
We show how to define a consistent braneworld cosmology in a model in which the brane is constructed as a field-theoretic domain wall of finite thickness. The Friedmann, Robertson-Walker metric is recovered in the region of the brane, but, remarkably, with scale factor that depends on particle energy and on particle species, constituting a breakdown of the weak equivalence principle on sufficiently small scales. This unusual effect comes from the extended nature of particles confined to a domain-wall brane, and the fact that they feel an "average" of the bulk spacetime. We demonstrate how to recover the standard results of brane cosmology in the infinitely-thin brane limit, and comment on how our results have the potential to place bounds on parameters such as the thickness of domain-wall braneworlds.
Using the worldline method, we derive an effective action of the bosonic sector of the Standard Model by integrating out the fermionic degrees of freedom. The CP violation stemming from the complex phase in the CKM matrix gives rise to CP-violating operators in the one-loop effective action in the next-to-leading order of a gradient expansion. We calculate the prefactor of the appropriate operators and give general estimates of CP violation in the bosonic sector of the Standard Model. In particular, we show that the effective CP violation for weak gauge fields is not suppressed by the Yukawa couplings of the light quarks and is much larger than the bound given by the Jarlskog determinant.
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