How well is the modern-day starburst-AGN connection mirrored in the early Universe? This is starting to be answered by deep wide radio surveys such as ATLAS, which are giving us a new view of high redshift galaxies. For example, we find powerful radio-loud AGNs which look like star-forming spirals in the optical and infrared, a composite which is almost unknown in the modern Universe. We find radio-bright objects which are unexpectedly invisible in the infrared, and which may be very high redshift radio galaxies and quasars. And although the radio-far-infrared correlation for star-forming galaxies has now been extended down to microJy levels, we still cannot reliably distinguish between starburst and AGN. So what do we need to do to ensure that SKA and its pathfinders will be able to understand galaxy evolution in the early Universe?
One of the central features of the last 8 to 10 billion years of cosmic history has been the emergence of a well-populated red sequence of non-star-forming galaxies. A number of models of galaxy formation and evolution have been devised to attempt to explain this behavior. Most current models require feedback from supermassive black holes (AGN feedback) to quench star formation in galaxies in the centers of their dark matter halos (central galaxies). Such models make the strong prediction that all quenched central galaxies must have a large supermassive black hole (and, by association, a prominent bulge component). I show using data from the Sloan Digital Sky Survey that the observations are consistent with this prediction. Over 99.5% of red sequence galaxies with stellar masses in excess of 10^{10} M_{\sun} have a prominent bulge component (as defined by having a Sersic index n above 1.5). Those very rare red sequence central galaxies with little or no bulge (n<1.5) usually have detectable star formation or AGN activity; the fraction of truly quenched bulgeless central galaxies is <0.1% of the total red sequence population. I conclude that a bulge, and by implication a supermassive black hole, is an absolute requirement for full quenching of star formation in central galaxies. This is in agreement with the most basic prediction of the AGN feedback paradigm.
We model the extremely massive and luminous lens galaxy in the Cosmic Horseshoe Einstein ring system, recently discovered in the Sloan Digital Sky Survey. We use the semi-linear method of Warren & Dye (2003), which pixelises the source surface brightness distribution, to invert the Einstein ring for sets of parameterised lens models. Here, the method is refined by exploiting Bayesian inference to optimise adaptive pixelisation of the source plane and to choose between three differently parameterised models: a singular isothermal ellipsoid, a power law model and a NFW profile. The most probable lens model is the power law with a volume mass density that scales as r^(-1.96+/-0.02) and an axis ratio of ~0.8. The mass within the Einstein ring (i.e., within a cylinder with projected distance of ~30 kpc from the centre of the lens galaxy) is (5.02+/-0.09)*10^12 M_solar, and the mass-to-light ratio is ~30. Even though the lens lies in a group of galaxies, the preferred value of the external shear is almost zero. This makes the Cosmic Horseshoe unique amongst large separation lenses, as almost all the deflection comes from a single, very massive galaxy with little boost from the environment.
The efficiency of mid-infrared selection methods for finding obscured AGN is investigated using data in the \chandra Deep Field North. It is shown that samples of AGN candidates compiled on the basis of mid-infrared colours only suffer substantial contamination from normal galaxies. X-ray stacking analysis reveals a soft mean X-ray spectrum for these sources, consistent with Gamma~2.1. This suggests that star-forming galaxies and not obscured AGN dominate the stacked signal. In contrast AGN selection methods that combine mid-infrared with optical criteria are more successful in finding heavily obscured AGN candidates. A method similar to the one proposed by Fiore et al. (2008) is adopted to select extremely red objects (R-[3.6]>3.7mag) with high 24micron to optical flux ratio (f_24/f_R>1000). About 80% of these sources are not detected at X-ray wavelengths. Stacking the X-ray photons at the positions of these sources shows a flat mean X-ray spectrum (Gamma~0.8), which suggests Compton-thick sources, low-luminosity and moderately obscured (N_H~8e22) AGN, or a combination of the two. The mid-infrared colours and luminosities of these sources are consistent with ULIRGs at z~2, while HST/ACS images, available for the optically brighter of these sources, show disturbed optical morphologies in many of them. The evidence above suggests that this population includes systems in the process of formation.
While the high-z frontier of star formation rate (SFR) studies has advanced rapidly, direct measurements beyond z ~ 4 remain difficult, as shown by significant disagreements among different results. Gamma-ray bursts, owing to their brightness and association with massive stars, offer hope of clarifying this situation, provided that the GRB rate can be properly related to the SFR. The Swift GRB data reveal an increasing evolution in the GRB rate relative to the SFR at intermediate z; taking this into account, we use the highest-z GRB data to make a new determination of the SFR at z = 4-7. Our results exceed the lowest direct SFR measurements, and imply that no steep drop exists in the SFR up to at least z ~ 6.5. We discuss the implications of our result for cosmic reionization, the efficiency of the universe in producing stellar-mass black holes, and ``GRB feedback'' in star-forming hosts.
Multi-epoch radio-interferometric observations of young stellar objects can be used to measure their displacement over the celestial sphere with a level of precision that currently cannot be attained at any other wavelength. In particular, the accuracy achieved using carefully calibrated, phase-referenced observations with the Very Long Baseline Array is better than 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and the proper motion of any radio-emitting young star within several hundred parsecs of the Sun with an accuracy better than a few percents. Taking advantage of this situation, we have initiated a large project aimed mainly at measuring the distance to the nearest regions of star-formation (Taurus, Ophiuchus, Perseus, etc.). Here, we will present the results for several stars in Taurus and Ophiuchus, and show that the accuracy obtained is already more than one order of magnitude better than that of previous estimates. The proper motion obtained from the data can also provide important information, particularly in multiple stellar systems. To illustrate this point, we will present the case of the famous system T Tauri, where the VLBA data provide crucial information for the characterization of the orbital path.
As part of an astrometric program, we have used the Very Long Baseline Array to measure the trigonometric parallax of several young stars in the Taurus and Ophiuchus star-forming regions with great accuracy. Additionally, we have obtained an unprecedented sample of high-resolution (~ 1 mas) images of several young stellar systems. These images revealed that about 70% of the stars in our sample are very tight binary stars (with separations of a few mas). Since it is highly unlikely that 70% of all stars are such tight binaries, we argue that selection effects are at work.
We present spectroscopic evidence for a low-luminosity, low-excitation active galactic nucleus (AGN) in NGC 1042, powered by an intermediate-mass black hole. These findings are significant in that the AGN is coincident with a compact star cluster known to reside in the nucleus, thus providing an example where the two types of central mass concentration coexist. The existence of a central black hole is additionally remarkable in that NGC 1042 lacks a stellar bulge. Objects such as NGC 1042 may have an important role in testing theories for the genesis of massive black holes in galaxy nuclei, and the extent to which they are in symbiosis with the larger stellar host.
We describe observations with the Mopra radiotelescope designed to assess the feasibility of the H$_2$O maser southern Galactic plane survey (HOPS). We mapped two one-square-degree regions along the Galactic plane using the new 12 mm receiver and the UNSW Mopra spectrometer (MOPS). We covered the entire spectrum between 19.5 and 27.5 GHz using this setup with the main aims of finding out which spectral lines can be detected with a quick mapping survey. We report on detected emission from H$_2$O masers, NH$_3$ inversion transitions (1,1), (2,2) and (3,3), HC$_3$N (3-2), as well as several radio recombination lines.
We describe microwave and hard X-ray observations of strong quasiperiodic pulsations from the GOES X1.3 solar flare on 15 June 2003. The radio observations were made jointly by the Owens Valley Solar Array (OVSA), the Nobeyama Polarimeter (NoRP), and the Nobeyama Radioheliograph (NoRH). Hard X-ray observations were made by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Using Fourier analysis, we study the frequency- and energy-dependent oscillation periods, differential phase, and modulation amplitudes of the radio and X-ray pulsations. Focusing on the more complete radio observations, we also examine the modulation of the degree of circular polarization and of the radio spectral index. The observed properties of the oscillations are compared with those derived from two simple models for the radio emission. In particular, we explicitly fit the observed modulation amplitude data to the two competing models. The first model considers the effects of MHD oscillations on the radio emission. The second model considers the quasi-periodic injection of fast electrons. We demonstrate that quasiperiodic acceleration and injection of fast electrons is the more likely cause of the quasiperiodic oscillations observed in the radio and hard X-ray emission, which has important implications for particle acceleration and transport in the flaring sources.
Balmer and Paschen continuum emission as well as Balmer series lines of P Cygni-type profile from H_gamma through H_23 are revealed in the violet spectra of BM Gem, a carbon star associated with an oxygen-rich circumstellar shell (`silicate carbon star') observed with the high dispersion spectrograph (HDS) on the Subaru telescope. The blue-shifted absorption in the Balmer lines indicates the presence of an outflow, the line of sight velocity of which is at least 400 km s^-1, which is the highest outflow velocity observed to date in a carbon star. We argue that the observed unusual features in BM Gem are strong evidence for the presence of a companion, which should form an accretion disk that gives rise to both an ionized gas region and a high velocity, variable outflow. The estimated luminosity of ~0.2 (0.03-0.6) L_sun for the ionized gas can be maintained by a mass accretion rate to a dwarf companion of ~10^-8 M_sun yr^-1, while ~10^-10 M_sun yr^-1 is sufficient for accretion to a white dwarf companion. These accretion rates are feasible for some detached binary configurations on the basis of the Bond-Hoyle type accretion process. We concluded that the carbon star BM Gem is in a detached binary system with a companion of low mass and low luminosity. However, we are unable to determine whether this companion object is a dwarf or a white dwarf. The upper limits for binary separation are 210 AU and 930 AU for a dwarf and a white dwarf, respectively. We also note that the observed features of BM Gem mimic those of Mira (omi Cet), which may suggest actual similarities in their binary configurations and circumstellar structures.
We discuss the parametric instabilities of large-amplitude parallel propagating Alfven waves using the 2-D PIC simulation code. First, we confirmed the results in the past study [Sakai et al, 2005] that the electrons are heated due to the modified two stream instability and that the ions are heated by the parallel propagating ion acoustic waves. However, although the past study argued that such parallel propagating longitudinal waves are excited by transverse modulation of parent Alfven wave, we consider these waves are more likely to be generated by the usual, parallel decay instability. Further, we performed other simulation runs with different polarization of the parent Alfven waves or the different ion thermal velocity. Numerical results suggest that the electron heating by the modified two stream instability due to the large amplitude Alfven waves is unimportant with most parameter sets.
Recent numerical magnetohydrodynamic calculations by Braithwaite and collaborators support the `fossil field' hypothesis regarding the origin of magnetic fields in compact stars and suggest that the resistive evolution of the fossil field can explain the reorganisation and decay of magnetar magnetic fields. Here, these findings are modelled analytically by allowing the stellar magnetic field to relax through a quasistatic sequence of nonaxisymmetric, force-free states, by analogy with spheromak relaxation experiments, starting from a random field. Under the hypothesis that the force-free modes approach energy equipartition in the absence of resistivity, the output of the numerical calculations is semiquantitatively recovered: the field settles down to a linked poloidal-toroidal configuration, which inflates and becomes more toroidal as time passes. A qualitatively similar (but not identical) end state is reached if the magnetic field evolves by exchanging helicity between small and large scales according to an $\alpha$-dynamo-like, mean-field mechanism, arising from the fluctuating electromotive force produced by the initial random field. The impossibility of matching a force-free internal field to a potential exterior field is discussed in the magnetar context.
We present measurements of the fluorine abundance in a Galactic Bulge Asymptotic Giant Branch (AGB) star. The measurements were performed using high resolution K-band spectra obtained with the CRIRES spectrograph, which has been recently installed at ESO's VLT, together with state-of-the-art model atmospheres and synthetic spectra. This represents the first fluorine abundance measurement in a Galactic Bulge star, and one of few measurements of this kind in a third dredge-up oxygen-rich AGB star. The F abundance is found to be close to the solar value scaled down to the metallicity of the star, and in agreement with Disk giants that are comparable to the Bulge giant studied here. The measurement is of astrophysical interest also because the star's mass can be estimated rather accurately ($1.4 \lesssim M/\mathrm{M}_{\sun} \lesssim 2.0$). AGB nucleosynthesis models predict only a very mild enrichment of F in such low mass AGB stars. Thus, we suggest that the fluorine abundance found in the studied star is representative for the star's natal cloud, and that fluorine must have been produced at a similar level in the Bulge and in the Disk.
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
This paper presents the chemical abundance analysis of a sample of 27 red giant stars located in 4 popolous intermediate-age globular clusters in the Large Magellanic Cloud, namely NGC 1651, 1783, 1978 and 2173. This analysis is based on high-resolution (R ~ 47000) spectra obtained with the UVES@VLT spectrograph. For each cluster we derived up to 20 abundance ratios sampling the main chemical elemental groups, namely light odd-Z, alpha, iron-peak and neutron-capture elements. All the analysed abundance patterns behave similarly in the 4 clusters and also show negligible star-to-star scatter within each cluster. We find [Fe/H]=-0.30+-0.03, -0.35+-0.02, -0.38+-0.02 and -0.51+-0.03 dex for NGC 1651, 1783, 1978 and 2173, respectively. The measurement of light odd-Z nuclei gives slightly subsolar [Na/Fe] and a more significant [Al/Fe] depletion (~ -0.50 dex). The [alpha / Fe] abundance ratios are nearly solar, while the iron-peak elements well trace that one of the iron. s-process elements behave in a peculiar way: light s-elements give subsolar [Y/Fe] and [Zr/Fe] abundance ratios, while heavy s-elements give enhanced [Ba/Fe], [La/Fe] and [Nd/Fe] with respect to the solar values. Also, the [Eu/Fe] abundance ratio turns out to be enhanced (~ 0.4 dex).
With increasingly large data sets, weak lensing measurements are able to measure cosmological parameters with ever greater precision. However this increased accuracy also places greater demands on the statistical tools used to extract the available information. To date, the majority of lensing analyses use the two point-statistics of the cosmic shear field. These can either be studied directly using the two-point correlation function, or in Fourier space, using the power spectrum. But analyzing weak lensing data inevitably involves the masking out of regions or example to remove bright stars from the field. Masking out the stars is common practice but the gaps in the data need proper handling. In this paper, we show how an inpainting technique allows us to properly fill in these gaps with only $N \log N$ operations, leading to a new image from which we can compute straight forwardly and with a very good accuracy both the pow er spectrum and the bispectrum. We propose then a new method to compute the bispectrum with a polar FFT algorithm, which has the main advantage of avoiding any interpolation in the Fourier domain. Finally we propose a new method for dark matter mass map reconstruction from shear observations which integrates this new inpainting concept. A range of examples based on 3D N-body simulations illustrates the results.
While in the past spherodicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In the case of those objects that underwent a very late helium flash (called VLTP objects or ``born-again'' PNe) it seems to be different. The first, hydrogen-rich PN, is more or less round. The ejecta from the VLTP event, in contrast, are extremely asymmetrical.
We present a phase resolved spectral analysis of the X-ray binary 4U0115+63 based upon Beppo-Sax satellite observations. Three strong absorption lines have been detected at all phases. We interpreted them as a cyclotron resonant scattering. Existence of the fourth cyclotron line has been confirmed at some phases. The cyclotron feature is found to be strongly dependent on the phase of the source, while the continuum part of the spectrum depends on the phase relatively weakly. The cyclotron lines turned out to be very nonequidistant. The second line is almost always deeper then the first one. We discussed physical conditions in the active regions of the source, under which a cyclotron feature similar to the observed one can appear.
We generalize tensor-scalar theories of gravitation by the introduction of an abnormally weighting type of energy. This theory of tensor-scalar anomalous gravity is based on a relaxation of the weak equivalence principle that is now restricted to ordinary visible matter only. As a consequence, the convergence mechanism toward general relativity is modified and produces naturally cosmic acceleration as an inescapable gravitational feedback induced by the mass-variation of some invisible sector. The cosmological implications of this new theoretical framework are studied. From the Hubble diagram cosmological test \textit{alone}, this theory provides an estimation of the amount of baryons and dark matter in the Universe that is consistent with the independent cosmological tests of Cosmic Microwave Background (CMB) and Big Bang Nucleosynthesis (BBN). Cosmic coincidence is naturally achieved from a natural assumption on the amplitude of the scalar coupling strength. Finally, from the adequacy to supernovae data, we derive a new intriguing relation between the space-time dependancies of the gravitational coupling and the dark matter mass, providing an example of crucial constraint on microphysics from cosmology. This glimpses at a tempting new symmetry between the visible and invisible sectors, namely that the scalar charges of visible and invisible matter are exactly opposite.
We investigate the nature of a sample of star cluster candidates detected as stellar overdensities towards the Galactic anticentre. Taken from the catalogue of Froebrich, Scholz, and Raftery (FSR), the sample contains 28 star cluster candidates located within $|\Delta\ell|=20^\circ$ of the anticentre. These are all the candidates in that sector classified by FSR with a high probability of being star clusters. Our main goals are to determine the fraction of such candidates that are unknown star clusters, to derive their astrophysical parameters, and to investigate the relationship of cluster parameters with position in the Galaxy. When photometric and radial distribution properties are considered together, an important fraction of the stellar overdensities with a fluctuation level $\ga3\sigma$ are shown to be star clusters. Thus, catalogues of star cluster candidates, coupled to the present kind of study, are an important source for identifying unknown open clusters. Such efforts affect the understanding of the star-formation rate, cluster dynamical evolution, and Galactic structure, among others.
I present a simplified analytical model that simulates the evolution of the binary population in a dynamically evolving globular cluster. A number of simulations have been run spanning a wide range in initial cluster and environmental conditions by taking into account the main mechanisms of formation and destruction of binary systems. Following this approach, I investigate the evolution of the fraction, the radial distribution, the distribution of mass ratios and periods of the binary population. According to these simulations, the fraction of surviving binaries appears to be dominated by the processes of binary ionization and evaporation. In particular, the frequency of binary systems changes by a factor 1-5 depending on the initial conditions and on the assumed initial distribution of periods. The comparison with the existing estimates of binary fractions in Galactic globular clusters suggests that significant variations in the initial binary content could exist among the analysed globular cluster. This model has been also used to explain the observed discrepancy found between the most recent N-body and Monte Carlo simulations in the literature.
The LMC and SMC are rich in binary star clusters, and some mergers are expected. It is important to characterize single clusters, binary clusters and candidates to mergers. We selected a sample of star clusters in each Cloud with this aim. Surface photometry of 25 SMC and 22 LMC star clusters was carried with the ESO Danish 1.54 m telescope. 23 clusters were observed for the first time for these purposes. We fitted Elson, Fall and Freeman (1987, EFF) profiles to the data, deriving structural parameters, luminosities and masses. We also use isophotal maps to constrain candidates to cluster interactions.} {The structural parameters, luminosities and masses presented good agreement with those in the literature. Three binary clusters in the sample have a double profile. Four clusters (NGC 376, K 50, K 54 and NGC 1810) do not have companions and present as well important deviations from EFF profiles. The present sample contains blue and red Magellanic clusters. Extended EFF profiles were detected in some blue clusters. We find evidence that important deviations from the body of EFF profiles might be used as a tool to detect cluster mergers.
The evolution of the Milky Way bulge and its relationship with the other Galactic populations is still poorly understood. The bulge has been suggested to be either a merger-driven classical bulge or the product of a dynamical instability of the inner disk. To probe the star formation history, the initial mass function and stellar nucleosynthesis of the bulge, we performed an elemental abundance analysis of bulge red giant stars. We also completed an identical study of local thin disk, thick disk and halo giants to establish the chemical differences and similarities between the various populations. High-resolution infrared spectra of 19 bulge giants and 49 comparison giants in the solar neighborhood were acquired with Gemini/Phoenix. All stars have similar stellar parameters but cover a broad range in metallicity. A standard 1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O and Fe. A homogeneous and differential analysis of the bulge, halo, thin disk and thick disk stars ensured that systematic errors were minimized. We confirm the well-established differences for [O/Fe] (at a given metallicity) between the local thin and thick disks. For the elements investigated, we find no chemical distinction between the bulge and the local thick disk, which is in contrast to previous studies relying on literature values for disk dwarf stars in the solar neighborhood. Our findings suggest that the bulge and local thick disk experienced similar, but not necessarily shared, chemical evolution histories. We argue that their formation timescales, star formation rates and initial mass functions were similar.
The Galaxy Mass Assembly ultra-deep Spectroscopic Survey samples a part of the CDFS to unprecedented depth. The resulting distribution of 150 z>1.4 redshifts reveals a significant peak at z=1.6, part of a larger overdensity found at this redshift. The 42 spectroscopic members of this structure, called Cl 0332-2742, form an overdensity in redshift of a factor 11+/-3 and have a velocity dispersion of 450 km/s. We derive a total mass for Cl 0332-2742 of ~7x10^14 Msol. The colours of its early-type galaxies are consistent with a theoretical red sequence of galaxies with stars formed at z=3.0. In addition, there are more massive, passive and older, but less star forming galaxies in CL 0332-2742 than in the field. We conclude that this structure is a cluster under assembly at z=1.6.
We present the first high spatial resolution monitoring of the dust forming nova V1280 Sco performed with the Very Large Telescope Interferometer (VLTI). Spectra and visibilities were obtained from the onset of the dust formation 23 days after discovery till day 145, using the instruments AMBER and MIDI. These interferometric observations are complemented by near-infrared data from the 1.2m Mt. Abu Infrared Observatory, India. The observations are first interpreted with simple models but more complex models, involving a second shell, are necessary to explain the data obtained from t=110d after outburst. This behavior is in accordance with the light curve of V1280 Sco which exhibits a secondary peak around t=106d, followed by a new steep decline, suggesting a new dust forming event. Spherical dust shell models generated with the DUSTY code are also used to investigate the parameters of the main dust shell. Using uniform disk and Gaussian models, these observations allow us to determine an apparent linear expansion rate for the dust shell of 0.35 +/- 0.03 mas/day and the approximate time of ejection of the matter in which dust formed as t_ejec=10.5+/-7d, i.e. close to the maximum brightness. This information, combined with the expansion velocity of 500+/-100km/s, implies a distance estimate of 1.6+/-0.4kpc. The dust mass generated was typically 2-8 10^-9 solar mass per day. Considering that the dust forming event lasted at least 200-250d, the mass of the ejected material is likely to have exceeded 10^-4 solar mass.
Despite a fainter Sun, the surface of the early Earth was mostly ice-free. Proposed solutions to this so-called "faint young Sun problem" have usually involved higher amounts of greenhouse gases than present in the modern-day atmosphere. However, geological evidence seemed to indicate that the atmospheric CO2 concentrations during the Archaean and Proterozoic were far too low to keep the surface from freezing. With a radiative-convective model including new, updated thermal absorption coefficients, we found that the amount of CO2 necessary to obtain 273 K at the surface is reduced up to an order of magnitude compared to previous studies. For the late Archaean and early Proterozoic period of the Earth, we calculate that CO2 partial pressures of only about 2.9 mb are required to keep its surface from freezing which is compatible with the amount inferred from sediment studies. This conclusion was not significantly changed when we varied model parameters such as relative humidity or surface albedo, obtaining CO2 partial pressures for the late Archaean between 1.5 and 5.5 mb. Thus, the contradiction between sediment data and model results disappears.
Using the Green Bank Telescope, we conducted a ``snapshot'' survey for water maser emission toward the nuclei of 611 galaxies and detected eight new sources. The sample consisted of nearby (v < 5000 km/s) and luminous (M_B < -19.5) galaxies, some with known nuclear activity but most not previously known to host AGNs. Our detections include both megamasers associated with AGNs and relatively low luminosity masers probably associated with star formation. The detection in UGC 3789 is particularly intriguing because the spectrum shows both systemic and high-velocity lines indicative of emission from an AGN accretion disk seen edge-on. Based on six months of monitoring, we detected accelerations among the systemic features ranging from 2 to 8 km/s/yr, the larger values belonging to the most redshifted systemic components. High-velocity maser lines in UGC 3789 show no detectable drift over the same period. Although UGC 3789 was not known to be an AGN prior to this survey, the presence of a disk maser is strong evidence for nuclear activity, and an optical spectrum obtained later has confirmed it. With follow up observations, it may be possible to measure a geometric distance to UGC 3789.
This paper is a comment on the McIntosh & Rustan (2007) and contains the proper interpretation of their result. Using velocity data published by them complemented by three additional historical velocities (Merrill 1935, 1950), we have estimated the orbital parameters of symbiotic Mira R Aqr. We find an eccentric orbit (e=0.4) with a period 40.9 yr. This solution is in agreement with a resolved VLA observation of this system (Hollis et al. 1997). We also discuss the connection between orbital motion and other phenomena shown by R Aqr.
We present a new compilation of Type Ia supernovae (SNe Ia), a new dataset of low-redshift nearby-Hubble-flow SNe and new analysis procedures to work with these heterogeneous compilations. This ``Union'' compilation of 414 SN Ia, which reduces to 307 SNe after selection cuts, includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey, the older datasets, as well as the recently extended dataset of distant supernovae observed with HST. A single, consistent and blind analysis procedure is used for all the various SN Ia subsamples, and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers. We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements (CMB and BAO). The constraint we obtain from supernovae on the dark energy density is $\Omega_\Lambda= 0.713^{+0.027}_{-0.029} (stat)}^{+0.036}_{-0.039} (sys)}$, for a flat, LCDM Universe. Assuming a constant equation of state parameter, $w$, the combined constraints from SNe, BAO and CMB give $w=-0.969^{+0.059}_{-0.063}(stat)^{+0.063}_{-0.066} (sys)$. While our results are consistent with a cosmological constant, we obtain only relatively weak constraints on a $w$ that varies with redshift. In particular, the current SN data do not yet significantly constrain $w$ at $z>1$. With the addition of our new nearby Hubble-flow SNe Ia, these resulting cosmological constraints are currently the tightest available.
The evolution leading to the formation of a neutron star in the very young Westerlund 1 star cluster is investigated. The turnoff mass has been estimated to be 35 Msun, indicating a cluster age ~ 3-5 Myr. The brightest X-ray source in the cluster, CXO J164710.2-455216, is a slowly spinning (10 s) single neutron star and potentially a magnetar. Since this source was argued to be a member of the cluster, the neutron star progenitor must have been very massive (M_zams > 40 Msun) as noted by Muno et al. (2006). Since such massive stars are generally believed to form black holes (rather than neutron stars), the existence of this object poses a challenge for understanding massive star evolution. We point out while single star progenitors below M_zams < 20 Msun form neutron stars, binary evolution completely changes the progenitor mass range. In particular, we demonstrate that mass loss in Roche lobe overflow enables stars as massive as 50-80 Msun, under favorable conditions, to form neutron stars. If the very high observed binary fraction of massive stars in Westerlund 1 (> 70 percent) is considered, it is natural that CXO J164710.2-455216 was formed in a binary which was disrupted in a supernova explosion such that it is now found as a single neutron star. Hence, the existence of a neutron star in a given stellar population does not necessarily place stringent constraints on progenitor mass when binary interactions are considered. It is concluded that the existence of a neutron star in Westerlund 1 cluster is fully consistent with the generally accepted framework of stellar evolution.
New 21cm HI observations made with the Green Bank Telescope show that the high-velocity cloud known as Smith's Cloud has a striking cometary appearance and many indications of interaction with the Galactic ISM. The velocities of interaction give a kinematic distance of 12.4 +/-1.3 kpc, consistent with the distance derived from other methods. The Cloud is >3 x 1 kpc in size and its tip at (l,b)=(39 deg,-13 deg) is 7.6 kpc from the Galactic center and 2.9 kpc below the Galactic plane. It has greater than 10^6 M solar masses in HI. Its leading section has a total space velocity near 300 km/s, is moving toward the Galactic plane with a velocity of 73+/-26 km/s, and is shedding material to the Galaxy. In the absence of drag the Cloud will cross the plane in about 27 Myr. Smith's Cloud may be an example of the accretion of gas by the Milky Way needed to explain certain persistent anomalies in Galactic chemical evolution.
Cosmic structure originated from minute density perturbations in an almost homogeneous universe. The first stars are believed to be very massive and luminous, providing the first ionizing radiation and heavy elements to the universe and forming 100 million years after the Big Bang. The impact from primordial stellar radiation is far reaching and affects subsequent star and galaxy formation. In this thesis, we present results from adaptive mesh refinement calculations of the formation of the first galaxies. We gradually introduce important physical processes, such as molecular hydrogen cooling and stellar feedback, to base models that only consider atomic hydrogen and helium cooling. In these base models, we find that gas in dark matter halos with masses ~10^8 solar masses centrally collapse before multiple fragmentation occurs in a global disc. We then investigate the importance of molecular hydrogen cooling in early structure formation in the presence of a soft ultraviolet radiation background. We find that molecular hydrogen plays an important role in star formation in halos well below a virial temperature of 10,000 K even in the most extreme assumptions of negative radiative feedback. We also present results from the first radiation hydrodynamics calculations of early dwarf galaxy formation. We develop a novel technique, adaptive ray tracing, to accurately transport radiation from primordial stars. We find primordial stellar feedback alters the landscape of early galaxy formation in that its angular momentum is increased and baryon fractions are decreased. We also describe the metal enrichment of the intergalactic medium and early dwarf galaxies. Finally we explore cosmological reionization by these massive, metal-free stars and its effects on star formation in early galaxies.
If there is a hidden photon -- i.e. a light abelian gauge boson in the hidden sector -- its kinetic mixing with the standard photon can produce a hidden cosmic microwave background (hCMB). For meV masses, resonant photon-hidden photon oscillations happen after nucleosynthesis (BBN) but before CMB decoupling, increasing the effective number of neutrinos but also the baryon to photon ratio. The current agreement between BBN and CMB data provides new constraints on the kinetic mixing. However, if one includes Lyman-alpha data, an effective number of neutrinos higher than 3 is preferred. It is tempting to interpret this effect in terms of the hCMB. Interestingly, the required parameters will be tested in the near future by laboratory experiments.
New optical spectra of Ca II and Na I toward HD 72127AB provide additional evidence for both spatial and temporal variations in the complex interstellar absorption along the two sight lines; archival UV spectra yield information on the abundances, depletions, and physical conditions in the gas toward HD 72127A. Similarities in the strengths of various tracers of interstellar material in the two lines of sight suggest that the total hydrogen column densities [N(H) ~ 2.5 x 10^{20} cm^{-2}] and the depletions and ionization in the main components at low LSR velocities also are similar. Toward HD 72127A, the main components are relatively cool (T < 900 K), but with depletions resembling those found in warm, diffuse disc clouds; the generally weaker components at higher velocities have much milder depletions, more like those found in halo clouds. Several trace neutral species -- Ca I, Cr I, and Fe I -- are much stronger toward HD 72127B, however. The column density of Cr I, for example, is about 30 times the value determined toward zeta Oph (the only previous detection of that species in the ISM). Dielectronic recombination in warmer gas (T > 5000 K) may be largely responsible for the enhanced abundances of those trace neutral species toward HD 72127B. If the main components toward HD 72127AB are associated with material in the Vela SNR, the differences in abundances and physical conditions occur on scales of about 1100 AU.
We use high-resolution simulations of large-scale structure formation to analyze the effects of interacting dark matter and dark energy on the evolution of the halo mass function. Using a chi-square likelihood analysis, we find significant differences in the mass function between models of coupled dark matter-dark energy and standard concordance cosmology Lambda-CDM out to redshift z=1.5. We also find a preliminary indication that the Dark Energy Survey should be able to distinguish these models from Lambda-CDM within its mass and redshift contraints. While we can distinguish the effects of these models from Lambda-CDM cosmologies with different fundamental parameters, DES will require independent measurements of sigma-8 to confirm these effects.
The extremely large hierarchy observed in the fermion mass spectrum remains as one of the most puzzling and unresolved issues in particle physics. In a recent proposal, however, it was demonstrated that by introducing one Higgs doublet (or Private Higgs) per fermion this hierarchy could be made natural by making the Yukawa couplings between each fermion and its respective Higgs boson of order unity. Among the interesting predictions of the Private Higgs scenario is a variety of scalars which could be probed at future collider experiments and a possible dark matter candidate. In this paper, we study perturbative unitarity in this model and show that, in general, the extended scalar sector of the Private Higgs model tends to soften the constraints on the Standard Model-like Higgs boson mass. We then calculate the annihilation cross sections of dark matter in this model and find that one can easily account for the observed density of dark matter in the Universe with relatively natural values of the model's parameters. Finally, we investigate the possibility of detecting Private Higgs dark matter indirectly via the observation of anomalous gamma rays originating from the galactic halo. We show that a substantial flux of photons can be produced from the annihilation of Private Higgs dark matter such that, if there is considerable clumping of dark matter in the galactic halo, the flux of these gamma rays could be observed by ground-based telescope arrays such as VERITAS and HESS.
We survey theoretical and experimental/observational results on general-relativistic spin (rotation) effects in binary systems. A detailed discussion is given of the two-body Kepler problem and its first post-Newtonian generalization, including spin effects. Spin effects result from gravitational spin-orbit and spin-spin interactions (analogous to the corresponding case in quantum electrodynamics) and these effects are shown to manifest themselves in two ways: (a) precession of the spinning bodies per se and (b) precession of the orbit (which is further broke down into precessions of the argument of the periastron, the longitude of the ascending node and the inclination of the orbit). We also note the ambiguity that arises from use of the terminology frame-dragging, de Sitter precession and Lense-Thirring precession, in contrast to the unambiguous reference to spin-orbit and spin-spin precessions. Turning to one-body experiments, we discuss the recent results of the GP-B experiment, the Ciufolini-Pavlis Lageos experiment and lunar-laser ranging measurements (which actually involve three bodies). Two-body systems inevitably involve astronomical observations and we survey results obtained from the first binary pulsar system, a more recently discovered binary system and, finally, the highly significant discovery of a double-pulsar binary system.
In order to derive the precise gravitational waveforms for extreme mass ratio inspirals (EMRI), we develop a formulation for the second order metric perturbations produced by a point particle moving in the Schwarzschild spacetime. The second order waveforms satisfy a wave equation with an effective source build up from products of the first order perturbations and its derivatives. We have explicitly regularized this source at the horizon and at spatial infinity. We show that the effective source does not contain squares of the Dirac's delta and that perturbations are regular at the particle location. We introduce an asymptotically flat gauge for the radiation fields and the $\ell=0$ mode to compute explicitly the (leading) second order $\ell=2$ waveforms in the headon collision case. This case represents the first completion of the radiation reaction program self-consistently.
Some formulae for the perturbations of the matter fields are summarized within the framework of the second-order gauge-invariant cosmological perturbation theory in a four dimensional homogeneous isotropic universe, which is developed in the papers [K. Nakamura, Prog. Theor. Phys. {\bf 117} (2005), 17.]. We derive the formulae for the perturbations of the energy momentum tensors and equations of motion in the cases of a perfect fluid, an imperfect fluid, and a signle scalar field, and show that all equations are derived in terms of gauge-invariant variables without any gauge fixing.
We update the D3/D7-brane inflation model on K3 x T^2/Z_2 with branes and fluxes. For this purpose, we study the low energy theory including g_s corrections to the gaugino condensate superpotential that stabilizes the K3 volume modulus. The gauge kinetic function is verified to become holomorphic when the original N=2 supersymmetry is spontaneously broken to N=1 by bulk fluxes. From the underlying classical N=2 supergravity, the theory inherits a shift symmetry which provides the inflaton with a naturally flat potential. We analyze the fate of this shift symmetry after the inclusion of quantum corrections. The field range of the inflaton is found to depend significantly on the complex structure of the torus but is independent of its volume. This allows for a large kinematical field range for the inflaton. Furthermore, we show that the D3/D7 model may lead to a realization of the recent CMB fit by Hindmarsh et al. with an 11% contribution from cosmic strings and a spectral index close to n_s=1. On the other hand, by a slight change of the parameters of the model one can strongly suppress the cosmic string contribution and reduce the spectral index n_s to fit the WMAP5 data in the absence of cosmic strings. We also demonstrate that the inclusion of quantum corrections allows for a regime of eternal D3/D7 inflation.
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The existence of massive galaxies with strongly suppressed star formation at z~2.3, identified in a previous paper, suggests that a red sequence may already be in place beyond z=2. In order to test this hypothesis, we study the rest-frame U-B color distribution of massive galaxies at 2<z<3. The sample is drawn from our near-infrared spectroscopic survey for massive galaxies. The color distribution shows a statistically significant (>3 sigma) red sequence, which hosts ~60% of the stellar mass at the high-mass end. The red-sequence galaxies have little or no ongoing star formation, as inferred from both emission-line diagnostics and stellar continuum shapes. Their strong Balmer breaks and their location in the rest-frame U-B, B-V plane indicate that they are in a post-starburst phase, with typical ages of ~0.5-1.0 Gyr. In order to study the evolution of the red sequence, we compare our sample with spectroscopic massive galaxy samples at 0.02<z<0.045 and 0.6<z<1.0. The rest-frame U-B color reddens by ~0.25 mag from z~2.3 to the present at a given mass. Over the same redshift interval, the number and stellar mass density on the high-mass end (>10^11 Msol) of the red sequence grow by factors of ~8 and ~6, respectively. We explore simple models to explain the observed evolution. Passive evolution models predict too strong d(U-B), and produce z~0 galaxies that are too red. More complicated models that include aging, galaxy transformations, and red mergers can explain both the number density and color evolution of the massive end of the red sequence between z~2.3 and the present.
Dissipative axisymmetric pulsar magnetosphere is calculated by a direct numerical simulation of the Strong-Field Electrodynamics equations. The magnetic separatrix disappears, it is replaced by a region of enhanced dissipation. With a better numerical scheme, one should be able to calculate the bolometric lightcurves for a given conductivity.
With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to undergo a sudden enhancement before the galaxy reaches the virial radius of the cluster. From a sample of 52 supercluster-scale filaments of galaxies joining a pair of rich clusters of galaxies within the two-degree Field Redshift Survey region, we find a significant enhancement of star formation, within a narrow range between 2-3 h/70 Mpc of the centre of the cluster into which the galaxy is falling. This burst of star formation is almost exclusively seen in the fainter dwarf galaxies (M_B> -20). The relative position of the peak does not depend on whether the galaxy is a member of a group or not, but non-group galaxies have on average a higher rate of star formation immediately before falling into a cluster. From the various trends, we conclude that the predominant process responsible for this rapid burst is the close interaction with other galaxies falling into the cluster along the same filament, if the interaction occurs before the gas reservoir of the galaxy gets stripped off due to the interaction with the intracluster medium.
{} {To quantify the amount of chaos that exists in the local phase space.} {A sample of orbits from four different models of the Solar neighbourhood phase space are analysed by a new chaos identification (and quantification) technique. While three of the used models bear the signature of the perturbation due to both the Galactic bar and the spiral pattern, the last of the models is a bar only one. We explore the models by inter-comparing the corresponding values of chaos strength that is induced at the various energy levels .}{(1) We find that of all the viable models that have been demonstrated to successfully reproduce the local phase space structure, i.e. those that include the bar as well as the spiral, bear strong chaoticity, though the model that implies the highest degree of chaos is the one in which overlap of the major resonances of the bar and the spiral occurs. The bar only model is found to display regularity. (2) We advance chaos to be primarily responsible for the splitting of the Hyades-Pleiades mode (the larger mode) of the local velocity distribution}{}
We show that most particle and subhalo orbits in simulated cosmological cold dark matter halos are surprisingly regular and periodic: The phase space structure of the outer halo regions shares some of the properties of the classical self-similar secondary infall model. Some of the outer branches are clearly visible in the radial velocity - radius plane at certain epochs. However, they are severely broadened in realistic, triaxial halos with non-radial, clumpy, mass accretion. This prevents the formation of high density caustics: Even in the best cases there are only broad, very small (<10 percent) enhancements in the spherical density profile. Larger fluctuations in rho(r) caused by massive satellites are common. Infall caustics are therefore too weak to affect lensing or dark matter annihilation experiments. Their detection is extremely challenging, as it requires a large number of accurate tracer positions and radial velocities in the outer halo. The stellar halo of the Milky Way is probably the only target where this could become feasible in the future.
We demonstrate an approach to solving the coagulation equation that involves using a finite number of moments of the particle size distribution. This approach is particularly useful when only general properties of the distribution, and their time evolution, are needed. The numerical solution to the integro-differential Smoluchowski coagulation equation at every time step, for every particle size, and at every spatial location is computationally expensive, and serves as the primary bottleneck in running evolutionary models over long periods of time. The advantage of using the moments method comes in the computational time savings gained from only tracking the time rate of change of the moments, as opposed to tracking the entire mass histogram which can contain hundreds or thousands of bins depending on the desired accuracy. The collision kernels of the coagulation equation contain all the necessary information about particle relative velocities, cross-sections, and sticking coefficients. We show how arbitrary collision kernels may be treated. We discuss particle relative velocities in both turbulent and non-turbulent regimes. We present examples of this approach that utilize different collision kernels and find good agreement between the moment solutions and the moments as calculated from direct integration of the coagulation equation. As practical applications, we demonstrate how the moments method can be used to track the evolving opacity, and also indicate how one may incorporate porous particles.
The link between turbulence in star formatting environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale-length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star forming environments. In the last section we contrast our work and its conclusions with previous studies which claim that jets can not be the source of turbulence.
The intimate links between gravitation and the second law are summarized and two less known relations between gravity and thermodynamics are studied. Firstly, the information cost required to operate a Maxwell's demon on a curved spacetime is estimated using the Kolmogorov-Sinai entropy. More importantly, the charge and time (C and T) reversal properties of the Kerr-Newman solution in General relativity show that this solution, similarly to the Dirac equation, appears to represent both a particle and its antiparticle and suggests a definition of antimatter in general relativity. This definition leads to a parameter free explanation of the cosmological constant term observed in the supernovae data. The relation of this definition of antimatter with the coupled systems through opposite time arrows studied by Schulman is also emphasized.
We carry out three-dimensional MHD simulations of star formation in turbulent, magnetized clouds, including ambipolar diffusion and feedback from protostellar outflows. The calculations focus on relatively diffuse clouds threaded by a strong magnetic field capable of resisting severe tangling by turbulent motions and retarding global gravitational contraction in the cross-field direction. They are motivated by observations of the Taurus molecular cloud complex (and, to a lesser extent, Pipe Nebula), which shows an ordered large-scale magnetic field, as well as elongated condensations that are generally perpendicular to the large-scale field. We find that stars form in earnest in such clouds when enough material has settled gravitationally along the field lines that the mass-to-flux ratios of the condensations approach the critical value. Only a small fraction (of order 1% or less) of the nearly magnetically-critical, condensed material is turned into stars per local free-fall time, however. The slow star formation takes place in condensations that are moderately supersonic; it is regulated primarily by magnetic fields, rather than turbulence. The quiescent condensations are surrounded by diffuse halos that are much more turbulent, as observed in the Taurus complex. Strong support for magnetic regulation of star formation in this complex comes from the extremely slow conversion of the already condensed, relatively quiescent C$^{18}$O gas into stars, at a rate two orders of magnitude below the maximum, free-fall value. We analyze the properties of dense cores, including their mass spectrum, which resembles the stellar initial mass function.
Automated techniques have been developed to automate the process of classification of objects or their analysis. The large datasets provided by upcoming spectroscopic surveys with dedicated telescopes urges scientists to use these automated techniques for analysis of such large datasets which are now available to the community. Sloan Digital Sky Survey (SDSS) is one of such surveys releasing massive datasets. We use Probabilistic Neural Network (PNN) for automatic classification of about 5000 SDSS spectra into 158 spectral type of a reference library ranging from O type to M type stars.
We use the spatial information of our previously published VLT/FORS2 absorption line spectroscopy to measure mean stellar velocity and velocity dispersion profiles of 25 field early-type galaxies at a median redshift z=0.97 (full range 0.6<z<1.2). This provides the first detailed study of early-type galaxy rotation at these redshifts. From surface brightness profiles from HST imaging we calculate two-integral oblate axisymmetric Jeans equation models for the observed kinematics. Fits to the data yield for each galaxy the degree of rotational support and the mass-to-light ratio M/L_Jeans. S0 and Sa galaxies are generally rotationally supported, whereas elliptical galaxies rotate less rapidly or not at all. Down to M(B)=-19.5 (corrected for luminosity evolution), we find no evidence for evolution in the fraction of rotating early-type (E+S0) galaxies between z=1 (63+/-11%) and the present (61+/-5%). We interpret this as evidence for little or no change in the field S0 fraction with redshift. We compare M/L_Jeans with M/L_vir inferred from the virial theorem and globally averaged quantities, and assuming homologous evolution. There is good agreement for non-rotating (mostly E) galaxies. However, for rotationally supported galaxies (mostly S0) M/L_Jeans is on average ~40% higher than M/L_vir. We discuss possible explanations and the implications for the evolution of M/L between z=1 and the present, and its dependence on mass.
The contrast of granulation is an important quantity characterizing solar surface convection. We compare the intensity contrast at 630 nm, observed using the Spectro-Polarimeter (SP) aboard the Hinode satellite, with the 3D radiative MHD simulations of V{\"o}gler & Sch{\"u}ssler (2007). A synthetic image from the simulation is degraded using a theoretical point-spread function of the optical system, and by considering other important effects. The telescope aperture and the obscuration by the secondary mirror and its attachment spider, reduce the simulated contrast from 14.4 % to 8.5 %. A slight effective defocus of the instrument brings the simulated contrast down to 7.5 %, close to the observed value of 7.0 %. A proper consideration of the effects of the optical system and a slight defocus, lead to sufficient degradation of the synthetic image from the MHD simulation, such that the contrast reaches almost the observed value. The remaining small discrepancy can be ascribed to straylight and slight imperfections of the instrument, which are difficult to model. Hence, Hinode SP data are consistent with a granulation contrast which is predicted by 3D radiation MHD simulations.
The neutral interstellar medium (ISM) inside the Local Bubble (LB) has been
known to have properties typical of the warm neutral medium (WNM). However,
several recent neutral hydrogen (HI) absorption experiments show evidence for
the existence of at least several cold diffuse clouds inside or at the boundary
of the LB, with properties highly unusual relative to the traditional cold
neutral medium. These cold clouds have a low HI column density, and AU-scale
sizes. As the kinematics of cold and warm gas inside the LB are similar, this
suggests a possibility of all these different flavors of the local ISM
belonging to the same interstellar flow. The co-existence of warm and cold
phases inside the LB is exciting as it can be used to probe the thermal
pressure inside the LB. In addition to cold clouds, several discrete screens of
ionized scattering material are clearly located inside the LB.
The cold exotic clouds inside the LB are most likely long-lived, and we
expect many more clouds with similar properties to be discovered in the future
with more sensitive radio observations. While physical mechanisms responsible
for the production of such clouds are still poorly understood, dynamical
triggering of phase conversion and/or interstellar turbulence are likely to
play an important role.
We have succeeded in establishing a cosmological model with a non-minimally coupled scalar field $\phi$ that can account not only for the spatial periodicity or the {\it picket-fence structure} exhibited by the galaxy $N$-$z$ relation of the 2dF survey but also for the spatial power spectrum of the cosmic microwave background radiation (CMB) temperature anisotropy observed by the WMAP satellite. The Hubble diagram of our model also compares well with the observation of Type Ia supernovae. The scalar field of our model universe starts from an extremely small value at around the nucleosynthesis epoch, remains in that state for sufficiently long periods, allowing sufficient time for the CMB temperature anisotropy to form, and then starts to grow in magnitude at the redshift $z$ of $\sim 1$, followed by a damping oscillation which is required to reproduce the observed picket-fence structure of the $N$-$z$ relation. To realize such behavior of the scalar field, we have found it necessary to introduce a new form of potential $V(\phi)\propto \phi^2\exp(-q\phi^2)$, with $q$ being a constant. Through this parameter $q$, we can control the epoch at which the scalar field starts growing.
We discuss the autocorrelation function $/zeta (r)$ for the sample 1157 radio-identified galaxies . The sample of galaxies is based on the Las Campanas Redshift Survey (LCRS) and 1.4 Ghz NRA)-VLA Sky Survey (NVSS) catalog of the radio sources. For separation $2-15h^{-1}$ Mpc autocorrelation function $/zeta (r)$$\gamma (s)$ can be approximated by the power law with correlation length and slope $-\gamma (s)=-1.8$. There are no clearly differences for correlation length between AGN and SB galaxies while value $\gamma$ for both samples are different: $\gamma=2.4$ for AGN and $\gamma=1.7$ for SB.
We present an investigation on effect of the ion-neutral (or ambipolar) diffusion heating rate on thermal phases of a molecular cloud. We use the modeling of ambipolar diffusion with two-fluid smoothed particle hydrodynamics, as discussed by Nejad-Asghar & Molteni. We take into account the ambipolar drift heating rate on the net cooling function of the molecular clouds, and we investigate the thermal phases in a self-gravitating magnetized one dimensional slab. The results show that the isobaric thermal instability criterion is satisfied in the outer parts of the cloud, thus, these regions are thermally unstable while the inner part is stable. This feature may be responsible for the planet formation in the outer parts of a collapsing molecular cloud and/or may also be relevant for the formation of star forming dense cores in the clumps.
High-resolution radio observations of nearby starburst galaxies have shown
that the distribution of their radio emission consists of a compact (<150 pc),
high surface brightness, central radio source immersed in a low surface
brightness circumnuclear halo. This radio structure is similar to that detected
in bright Seyferts galaxies like NGC 7469 or Mrk 331, which display clear
circumnuclear rings. While the compact, centrally located radio emission in
these starbursts might be generated by a point-like source (AGN), or by the
combined effect of multiple radio supernovae and supernova remnants (e.g., the
evolved nuclear starburst in Arp~220), it seems well established that the
circumnuclear regions of those objects host an ongoing burst of star-formation
(e.g., NGC 7469; Colina et al. 2001, Alberdi et al. 2006). Therefore,
high-resolution radio observations of Luminous Infra-Red Galaxies (LIRGs) in
our local universe are a powerful tool to probe the dominant dust heating
mechanism in their nuclear and circumnuclear regions.
In this contribution, we show results obtained from VLA-A, MERLIN, and EVN
(VLBI) radio observations of the galaxies NGC 7469 (D~70 Mpc) and IRAS
18293-3413 (D ~ 79 Mpc), where two extremely bright radio supernovae have been
found. High-resolution studies of these and other LIRGs would allow us to
determine the core-collapse supernova rate in them, as well as their
star-formation rate.
On basis of the theorem of a universal shower development stating that a hadronically generated extensive air shower is completely described by the primary energy, the position of the shower maximum and a parameter related to the total muon number, the so-called correlation curve method is developed and applied to KASCADE data. Correlation information of the muon and electron content of showers measured by the KASCADE experiment are used for the reconstruction of energy and mass of primary cosmic rays. Systematic uncertainties of the method and the results are discussed in detail. It is shown that by this method general tendencies in spectrum and composition indeed can be revealed, but the absolute normalization in energy and mass scale requires much more detailed simulations.
We present a statistical study of the effects induced by substructures on the deflection potential of dark matter halos in the strong lensing regime. This investigation is based on the pertubative solution around the Einstein radius (Alard 2007) in which all the information on the deflection potential is specified by only a pair of one-dimensional functions on this ring. Using direct comparison with ray-tracing solutions, we found that the iso-contours of lensed images predicted by the pertubative solution is reproduced with a mean error on their radial extension of less than 1% - in units of the Einstein radius, for reasonable substructure masses. It demonstrates the efficiency of the approximation to track possible signatures of substructures. We have evaluated these two fields and studied their properties for different lens configurations modelled either through massive dark matter halos from a cosmological N-body simulation, or via toy models of Monte Carlo distribution of substructures embedded in a triaxial Hernquist potential. As expected, the angular power spectra of these two fields tend to have larger values for larger harmonic numbers when substructures are accounted for and they can be approximated by power-laws, whose values are fitted as a function of the profile and the distribution of the substructures.
We demonstrate that the formation of collapsing cores in subcritical clouds is accelerated by nonlinear flows, by performing three-dimensional non-ideal MHD simulations. An initial random supersonic (and trans-Alfvenic) turbulent-like flow is input into a self-gravitating gas layer that is threaded by a uniform magnetic field (perpendicular to the layer) such that the initial mass-to-flux ratio is subcritical. Magnetic ambipolar diffusion occurs very rapidly initially due to the sharp gradients introduced by the turbulent flow. It subsequently occurs more slowly in the traditional near-quasistatic manner, but in regions of greater mean density than present in the initial state. The overall timescale for runaway growth of the first core(s) is several times, 10^6 yr, even though previous studies have found a timescale of several times, 10^7 yr when starting with linear perturbations and similar physical parameters. Large-scale supersonic flows exist in the cloud and provide an observationally testable distinguishing characteristic from core formation due to linear initial perturbations. However, the nonlinear flows have decayed sufficiently that the relative infall motions onto the first core are subsonic, as in the case of starting from linear initial perturbations. The ion infall motions are very similar to those of neutrals; however, they lag the neutral infall in directions perpendicular to the mean magnetic field direction and lead the neutral infall in the direction parallel to the mean magnetic field.
We report on a S/N-limited search for low-ionization gas outflows in the spectra of the 0.11 < z < 0.54 objects in the EGS portion of the DEEP2 survey. Doppler shifts from the host galaxy redshifts are systematically searched for in the Na I 5890,96 doublet (Na D). Although the spectral resolution and S/N limit us to study the interstellar gas kinematics from fitting a single doublet component to each observed Na D profile, the typical outflow often seen in local luminous-infrared galaxies (LIRGs) should be detected at >~ 6 sigma in absorption equivalent width down to the survey limiting S/N (~ 5 per pixel) in the continuum around Na D. The detection rate of LIRG-like outflow clearly shows an increasing trend with star-forming activity and infrared luminosity. However, by virtue of not selecting our sample on star formation, we also find a majority of outflows in galaxies on the red sequence in the rest-frame (U-B, M_B) color-magnitude diagram. Most of these red-sequence outflows are of early-type morphology and show the sign of recent star formation in their UV-optical colors; some show enhanced Balmer H-beta absorption lines indicative of poststarburst as well as high dust extinction. These findings suggest that galactic-scale outflow may play an important role in quenching star formation in the host galaxies on their way to the red sequence. Furthermore, outflows well outlive starbursts and present significant columns over a relatively long timescale of ~ Gyr, so the fate of relic winds as well as the observational constraints on the gaseous feedback models may be studied well in galaxies at their poststarburst phase. We also note the presence of inflow candidates in red, early-type galaxies, some with signs of AGN/LINERs but little evidence for star formation.
The observed fraction of pulsars with interpulses, their period distribution and the observed pulse width versus pulse period correlation is shown to be inconsistent with a model in which the angle alpha between the magnetic axis and the rotation axis is random. This conclusion appears to be unavoidable, even when non-circular beams are considered. Allowing the magnetic axis to align from a random distribution at birth with a timescale of 70 Myrs years can, however, explain those observations well. The timescale derived is consistent with that obtained via independent methods. The probability that a pulsar beam intersects the line of sight is a function of the angle alpha and therefore beam evolution has important consequences for evolutionary models and for estimations of the total number of neutron stars. The validity of the standard formula for the spin-down rate, which is independent of alpha appears to be questionable.
We revisit a weak gravitational lensing problem by constructing a setup which describes the actual system as accurately as possible and solving the null geodesic equations. Details are given for the case of a Universe driven only by a cosmological constant, \Lambda, which confirm the conventional results: The conventional lensing analysis is correct as it is, without any need for correction of O(\Lambda). We also treat the cases of the lensing in generic FRW backgrounds.
We show that dust matter-dark energy combined phases can be achieved by the exact solution derived from a power law $f(R)$ cosmological model. This example answers the query by which a dust-dominated decelerated phase, before dark-energy accelerated phase, is needed in order to form large scale structures.
We study the effect of modified gravity on weak lensing in a class of scalar-tensor theory that includes $f(R)$ gravity as a special case. These models are designed to satisfy local gravity constraints by having a large scalar-field mass in a region of high curvature. Matter density perturbations in these models are enhanced at small redshifts because of the presence of a coupling $Q$ that characterizes the strength between dark energy and non-relativistic matter. We compute a convergence power spectrum of weak lensing numerically and show that the spectral index and the amplitude of the spectrum in the linear regime can be significantly modified compared to the $\Lambda$CDM model for large values of $|Q|$ of the order of unity. Thus weak lensing provides a powerful tool to constrain such large coupling scalar-tensor models including $f(R)$ gravity.
The main observational properties and resulting classification of supernovae (SNe) are briefly reviewed. Then we discuss the progress in modeling of two basic types of SNe - the thermonuclear and core-collapse ones, with special emphasis being placed on difficulties relating to a consistent description of thermonuclear flame propagation and the detachment of supernova envelope from the collapsing core (a nascent neutron star). The properties of the neutrino flux expected from the corecollapse SNe, and the lessons of SN1987A, exploded in the Large Magellanic Cloud, are considered as well.
We present spectroscopic and photometric observations of the eclipsing binary V32 located in the central field of the globular cluster NGC 6397. The variable is a single-line spectroscopic binary with an orbital period of 9.8783d and a large eccentricity of e=0.32. Its systemic velocity (gamma=20.7 km/s) and metallicity ([Fe/H] -1.9) are both consistent with cluster membership. The primary component of the binary is located at the top of the main-sequence turn-off on the cluster color-magnitude diagram. Only a shallow primary eclipse is observed in the light curve. Based on stellar models for an age of 12Gyr and the mass-function derived from the radial velocity curve, we estimate the masses to be M_p=0.79 Msun and M_s=0.23 Msun. The light curve of V32 can be reproduced by adopting R_p=1.569 Rsun and R_s=0.236 Rsun for the radii and i=85.44 deg for the system inclination. The system geometry precludes observations of the secondary eclipse. The large eccentricity of the orbit is puzzling given that for metal poor, halo binaries the transition from circular to eccentric orbit occurs at an orbital period of about 20 days. We suppose that the orbit of V32 was modified relatively recently by dynamical interaction with other cluster star(s).An alternative explanation of the observed eccentricity calls for the presence of a third body in the system.
We present a detailed analysis of two-band HST/ACS imaging of 21 ultra-compact dwarf (UCD) galaxies in the Virgo and Fornax Clusters. The aim of this work is to test two formation hypotheses for UCDs--whether they are bright globular clusters (GCs) or "threshed'' early-type dwarf galaxies--by comparison of UCD structural parameters and colors with GCs and galaxy nuclei. We find that the UCD surface brightness profiles can be described by a range of models and that the luminous UCDs can not be described by standard King models with tidal cutoffs as they have extended outer halos. This is not expected from traditional King models of GCs, but is consistent with recent results for massive GCs. The total luminosities, colors and sizes of the UCDs are consistent with them being either luminous GCs or threshed nuclei of both early-type and late-type galaxies (not just early-type dwarfs). For the most luminous UCDs we estimate color gradients over a limited range of radius. These are systematically positive in the sense of getting redder outwards: mean Delta(F606W-F814W)=0.14 mag per 100 pc with rms=0.06 mag per 100 pc. The positive gradients found in the bright UCDs are consistent with them being either bright GCs or threshed early-type dwarf galaxies (except VUCD3). In contrast to the above results we find a very significant difference in the sizes of UCDs and early-type galaxy nuclei: the effective radii of UCDs are 2.2 times larger than those of early-type galaxy nuclei at the same luminosity. This result suggests an important test can be made of the threshing hypothesis by simulating the process and predicting what size increase is expected.
Mode identification is crucial for an asteroseismological study of any significance. Contrarily to spectroscopic techniques, methods such as period-fitting and multi-colour photometry do not provide a full reconstruction of non-radial pulsations. We present a new method of spectroscopic mode identification and test it on time-series of synthetic spectra appropriate for pulsating subdwarf-B stars. We then apply it to the newly discovered slowly pulsating subdwarf-B star HD 4539.
A chemical evolution model for the bimodal-like abundance distribution in the external galaxy M51 recently derived on the basis of HST data for more than a half million red supergiants is developed. It is shown that, like in our Galaxy, formation of fine structure of the radial abundance pattern -- a rather steep gradient in the internal part of the disc and a plateau in the middle part -- is due to the influence of the spiral arms, the bend in the slope of the distribution being arose near the corotation resonance. Our model strongly suggests that M51 is surrounded by overabundant gas infalling onto its disc.
We present and discuss the results of an extensive observational campaign devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift satellite. This event was followed for almost a month in the optical/near-infrared (NIR) with various telescopes starting from about 2min after the high-energy event. Swift-XRT observations started only later at about 0.4d. The light-curve evolution allows us to single out an initial rising phase with a maximum at about 7min, possibly the afterglow onset in the context of the standard fireball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6d. The rebrightening was visible in both the optical/NIR and X-rays and can be interpreted as an episode of discrete energy injection, although various alternatives are possible. A steepening of the afterglow light curve is recorded at about 1d. The entire evolution of the optical/NIR afterglow is consistent with being achromatic. This could be one of the few identified GRB afterglows with an achromatic break in the X-ray through the optical/NIR bands. Polarimetry was also obtained at about 1d, just after the rebrightening and almost coincident with the steepening. This provided a fairly tight upper limit of 0.9% for the polarized-flux fraction.
Asteroseismology of Sun-like stars is undergoing rapid expansion with, for example, new data from the CoRoT mission and continuation of ground-based campaigns. There is also the exciting upcoming prospect of NASA's Kepler mission, which will allow the asteroseismic study of several hundred Sun-like targets, in some cases for periods lasting up to a few years. The seismic mode parameters are the input data needed for making inference on stars and their internal structures. In this paper we discuss the ease with which it will be possible to extract estimates of individual mode parameters, dependent on the mass, age, and visual brightness of the star. Our results are generally applicable; however, we look at mode detectability in the context of the upcoming Kepler observations. To inform our discussions we make predictions of various seismic parameters. To do this we use simple empirical scaling relations and detailed pulsation computations of the stochastic excitation and damping characteristics of the Sun-like p modes. The issues related to parameter extraction on individual p modes discussed here are mode detectability, the detectability and impact of stellar activity cycles, and the ability to measure properties of rotationally split components, which is dependent on the relative importance of the rotational characteristics of the star and the damping of the stochastically excited p modes.
We discuss recently published results of two-dimensional measurements of the cosmic ray anisotropy in the energy range 1-100 TeV. It is demonstrated that, in spite of pretence of the authors to measure the anisotropy in more detail than it was done in one-dimensional measurements of the first harmonic of CR intensity in sidereal time, new measurements give nothing essentially new. Moreover, two-dimensional picture is misleading creating an illusion that the true direction of the anisotropy is observed, while, as before, only the projection of the anisotropy onto the equatorial plane is measured and the phase of the anisotropy remains to be the only directly measured parameter. The sophisticated interpretations of the results of 2D measurements made by their authors are invalid, since they are based on the false assumption that the equatorial excess and deficit of CR intensity seen on the difference maps represent the real anisotropy.
We present the observational properties of the dwarf galaxy population (Mr > M*+1) corresponding to one of the largest samples of spectroscopically confirmed galaxy cluster members reported in the literature. We have observed that red dwarf galaxies (u-r > 2.22) share the same cluster environment as the brightest cluster members (Mr < -21), but are not in dynamical equilibrium. We computed the dwarf-to-giant ratio (DGR) using a spectroscopically selected sample. The DGR was found to vary with clustercentric distance, essentially due to the blue dwarf population (u-r < 2.22). The u-r color of red dwarf galaxies was independent of their environment and similar to the color of red isolated dwarfs. Blue dwarf galaxies located outside r200 show similar u-r colors to those of the field population, while strong reddening was observed toward the cluster center. We also present evidence that the fraction of red to blue dwarf galaxies in clusters is larger in the innermost cluster regions. We conclude that the present red dwarf population observed in the central regions of nearby galaxy clusters could be related to the blue dwarf population observed in clusters at high redshift.
Multiwavelength studies of the seven identified X-ray dim isolated neutron stars (XDINSs) offer a unique opportunity to investigate their surface thermal and magnetic structure and the matter-radiation interaction in presence of strong gravitational and magnetic fields. As a part of an ongoing campaign aimed at a complete identification and spectral characterization of XDINSs in the optical band, we performed deep imaging with the ESO Very Large Telescope (VLT) of the field of the XDINS RBS1774 (1RXS J214303.7 +065419). The recently upgraded FORS1 instrument mounted on the VLT provided the very first detection of a candidate optical counterpart in the B band. The identification is based on a very good positional coincidence with the X-ray source (chance probability ~2E-3). The source has B=27.4 +/- 0.2 (1 sigma confidence level), and the optical flux exceeds the extrapolation of the X-ray blackbody at optical wavelengths by a factor ~35 (+/- 20 at 3sigma confidence level). This is barely compatible with thermal emission from the neutron star surface, unless the source distance is d~200-300 pc, and the star is an almost aligned rotator or its spin axis is nearly aligned with the line of sight. At the same time, such a large optical excess appears difficult to reconcile with rotation-powered magnetospheric emission, unless the source has an extremely large optical emission efficiency. The implications and possible similarities with the optical spectra of other isolated NSs are discussed.
Recently, crust cooling times have been measured for neutron stars after extended outbursts. These observations are very sensitive to the thermal conductivity $\kappa$ of the crust and strongly suggest that $\kappa$ is large. We perform molecular dynamics simulations of the structure of the crust of an accreting neutron star using a complex composition that includes many impurities. The composition comes from simulations of rapid proton capture nucleosynthesys followed by electron captures. We find an ordered crystal structure with a high thermal conductivity that is in agreement with observation. We do not find an amorphous solid that could have a low conductivity.
We present results of fully self-consistent N-body simulations of the motion of four globular clusters moving in the inner region of their parent galaxy. With regard to previous simplified simulations, we confirm merging and formation of an almost steady nuclear cluster, in a slightly shorter time. The projected surface density profile shows strong similarity to that of resolved galactic nuclei. This similarity reflects also in the velocity dispersion profile which exhibits a central colder component as observed in many nucleated galaxies.
A numerical model of axisymmetric convection in the presence of a vertical magnetic flux bundle and rotation about the axis is presented. The model contains a compressible plasma described by the nonlinear MHD equations, with density and temperature gradients simulating the upper layer of the sun's convection zone. The solutions exhibit a central magnetic flux tube in a cylindrical numerical domain, with convection cells forming collar flows around the tube. When the numerical domain is rotated with a constant angular velocity, the plasma forms a Rankine vortex, with the plasma rotating as a rigid body where the magnetic field is strong, as in the flux tube, while experiencing sheared azimuthal flow in the surrounding convection cells, forming a free vortex. As a result, the azimuthal velocity component has its maximum value close to the outer edge of the flux tube. The azimuthal flow inside the magnetic flux tube and the vortex flow are prograde relative to the rotating cylindrical reference frame. A retrograde flow appears at the outer wall. The most significant convection cell outside the flux tube is the location for the maximum value of the azimuthal magnetic field component. The azimuthal flow and magnetic structure are not generated spontaneously, but decay exponentially in the absence of any imposed rotation of the cylindrical domain.
We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015-2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0<z<2 down to AB~23 over 3\pi sr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB~26 and at 2<z<10+. These goals are unreachable with ground-based observations due to the ~500 times higher sky background. To achieve the main science objectives, SPACE will use a 1.5m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices (DMDs) covering a total field of view of 0.4 deg2, and will perform large-multiplexing multi-object spectroscopy (e.g. ~6000 targets per pointing) at a spectral resolution of R~400 as well as diffraction-limited imaging with continuous coverage from 0.8mum to 1.8mum.
We present $UBVRI$ CCD photometry and optical spectra of the type Ia supernova SN 2003hx which appeared in the galaxy NGC 2076, obtained till $\sim$ 146 days after the epoch of $B$ band maximum. The supernova reached at maximum brightness in $B$ band on JD 245 2893 $\pm$ 1.0 with an apparent magnitude of 14.92 $\pm$ 0.01 mag which was estimated by making template fits to the light curves. SN 2003hx is an example of a highly reddened supernova with $E(B-V)$ = 0.56 $\pm$ 0.23. We estimate $R_v$ = 1.97 $\pm$ 0.54 which indicates the small size of dust particles as compared to their galactic counterparts. The luminosity decline rate is $\Delta m_{15}(B)$ = 1.17 $\pm$ 0.12 mag and the absolute $B$ band magnitude obtained from the luminosity versus decline rate relation (Phillips et al. 1999) is $M^B_{max}$ = -19.20 $\pm$ 0.18 mag. The peak bolometric luminosity indicates that $\sim$ 0.66 $M_\odot$ mass of $^{56}$ Ni was ejected by the supernova. The spectral evolution indicates the supernova to be a normal type Ia event.
We present a method which extends Monte Carlo studies to situations that require a large dynamic range in particle number. The underlying idea is that, in order to calculate the collisional evolution of a system, some particle interactions are more important than others and require more resolution, while the behavior of the less important, usually of smaller mass, particles can be considered collectively. In this approximation groups of identical particles, sharing the same mass and structural parameters, operate as one unit. The amount of grouping is determined by the zoom factor -- a free parameter that determines on which particles the computational effort is focused. Two methods for choosing the zoom factors are discussed: the `equal mass method,' in which the groups trace the mass density of the distribution, and the `distribution method,' which additionally follows fluctuations in the distribution. Both methods achieve excellent correspondence with analytic solutions to the Smoluchowski coagulation equation. The grouping method is furthermore applied to simulations involving runaway kernels, where the particle interaction rate is a strong function of particle mass, and to situations that include catastrophic fragmentation. For the runaway simulations previous predictions for the decrease of the runaway timescale with the initial number of particles ${\cal N}$ are reconfirmed, extending ${\cal N}$ to $10^{160}$. Astrophysical applications include modeling of dust coagulation, planetesimal accretion, and the dynamical evolution of stars in large globular clusters. The proposed method is a powerful tool to compute the evolution of any system where the particles interact through discrete events, with the particle properties characterized by structural parameters.
Recent radiative lifetime measurements accurate to +/- 5% (Stockett et al. 2007, J. Phys. B 40, 4529) using laser-induced fluorescence (LIF) on 8 even-parity and 62 odd-parity levels of Er II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 418 lines of Er II. This work moves Er II onto the growing list of rare earth spectra with extensive and accurate modern transition probability measurements using LIF plus FTS data. This improved laboratory data set has been used to determine a new solar photospheric Er abundance, log epsilon = 0.96 +/- 0.03 (sigma = 0.06 from 8 lines), a value in excellent agreement with the recommended meteoric abundance, log epsilon = 0.95 +/- 0.03. Revised Er abundances have also been derived for the r-process-rich metal-poor giant stars CS 22892-052, BD+17 3248, HD 221170, HD 115444, and CS 31082-001. For these five stars the average Er/Eu abundance ratio, <log epsilon (Er/Eu)> = 0.42, is in very good agreement with the solar-system r-process ratio. This study has further strengthened the finding that r-process nucleosynthesis in the early Galaxy which enriched these metal-poor stars yielded a very similar pattern to the r-process which enriched later stars including the Sun.
We study the variability of the warm absorber and the gas responsible for the emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the location and physical properties of these components. Using X-ray spectra taken with the \textit{Chandra}$-$LETGS in 2002 and 2005, we study variability in the ionic column densities and line intensities. We find a lower \ion{O}{vii} forbidden emission line flux in 2005, while the Fe K$\alpha$ line flux stays constant. The warm absorber is less ionized in 2005, allowing us to constrain its location to within 7 pc of the central source. Using both the observed variability and the limit on the FWHM of the \ion{O}{vii} f line, we have constrained the location of the narrow line region to a distance of 1 pc from the central source. The apparent lack of variability of the Fe K$ \alpha$ line flux does not allow for a unique explanation.
This paper represents an in-depth treatment of the chain inflation scenario. We fully determine the evolution of the universe in the model, the necessary conditions in order to have a successful inflationary period, and the matching with the observational results regarding the cosmological perturbations. We study in great detail, and in general, the dynamics of the background, as well as the mechanism of generation of the perturbations. We also find an explicit formula for the spectrum of adiabatic perturbations. Our results prove that chain inflation is a viable model for solving the horizon, entropy and flatness problem of standard cosmology and for generating the right amount of adiabatic cosmological perturbations. The results are radically different from those found in previous works on the subject. Finally, we argue that there is a natural way to embed chain inflation into flux compactified string theory. We discuss the details of the implementation and how to fit observations.
Motivated by the recent work on a new physical interpretation of quasinormal modes by Maggiore, we utilize this new proposal to the interesting case of Kerr black hole. In particular, by modifying Hod's idea, the resulting black hole horizon area is quantized and the resulting area quantum is in full agreement with Bekenstein's result. Furthermore, in an attempt to show that the area spectrum is equally spaced, we follow Kunstatter's method. We propose a new interpretation as a result of Maggiore's idea, for the frequency that appears in the adiabatic invariant of a black hole. The derived area spectrum is similar to that of the quantum-corrected Kerr black hole but it is not equally spaced.
The f(R) gravity field equations are derived as an equation of state of local space-time thermodynamics. Jacobson's arguments are non-trivially extended, by means of a more general definition of local entropy, for which Wald's definition of dynamic black hole entropy is used, as well as the concept of an effective Newton constant for graviton exchange, recently appeared in the literature.
The analysis method currently proposed to search for isotropic stochastic radiation of primordial or astrophysical origin with the Laser Interferometer Space Antenna (LISA) relies on the combined use of two LISA channels, one of which is insensitive to gravitational waves, such as the symmetrised Sagnac. For this method to work, it is essential to know how the instrumental noise power in the two channels are related to one another; however, no quantitative estimates of this key information are available to date. The purpose of our study is to assess the performance of the symmetrised Sagnac method for different levels of prior information regarding the instrumental noise. We develop a general approach in the framework of Bayesian inference and an end-to-end analysis algorithm based on Markov Chain Monte Carlo methods to compute the posterior probability density functions of the relevant model parameters. We apply this method to data released as part of the second round of the Mock LISA Data Challenges. For the selected (and somewhat idealised) cases considered here, we find that a prior uncertainty of a factor ~2 in the ratio between the power of the instrumental noise contributions in the two channels allows for the detection of isotropic stochastic radiation. More importantly, we provide a framework for more realistic studies of LISA's performance and development of analysis techniques in the context of searches for stochastic signals.
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We present HST photometry and Keck spectroscopy of globular clusters (GCs) in the nearby S0 galaxy NGC 7457. The V-I color-magnitude diagram of GCs lacks the clear bimodality present in most early-type galaxies; there may be a significant population of intermediate-color objects. Of 13 spectroscopically-observed GCs, two are unusually metal-rich and feature bright [O III] emission lines. We conclude that one probably hosts a planetary nebula and the other a supernova remnant. Such emission line objects should be more common in an intermediate-age stellar population than in an old one. We therefore suggest that, in addition to the typical old metal-rich and old metal-poor GC subpopulations, there may be a third subpopulation of intermediate age. Such a subpopulation may have been formed ~2-3 Gyr ago, in the same star-forming event that dominates the stellar population of the center of the galaxy.
The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from -2.5 to +0.5, [alpha/Fe] from -0.2 to +0.8 (for [Fe/H] <=0) or +0.2 (for [Fe/H] >0), and initial He mass fractions from Y=0.245 to 0.40. Stellar evolution tracks were computed for masses between 0.1 and 4 Msun, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)c, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS-WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a website at this http URL where all tracks, isochrones, and additional files can be downloaded.
We investigate the population of z=3 damped Lyman alpha absorbers (DLAs) in a
recent series of high resolution galaxy formation simulations. The simulations
are of interest because they form at z=0 some of the most realistic disk
galaxies to date. No free parameters are available in the simulations: these
have been fixed by physical and z=0 observational constraints, and thus our
study provides a genuine consistency test. The precise role of DLAs in galaxy
formation remains in debate, but they provide a number of strong constraints on
the nature of our simulated bound systems at z=3 because of their coupled
information on neutral H I densities, kinematics, metallicity and estimates of
star formation activity.
Our results, without any parameter-tuning, closely match the observed
incidence rate and column density distributions of DLAs. Our simulations are
the first to reproduce the distribution of metallicities (with a median of
Z_{DLA} = Z_{solar}/20) without invoking observationally unsupported mechanisms
such as dust biasing. This is especially encouraging given that these
simulations have previously been shown to have a realistic 0<z<2 stellar
mass-metallicity relation. Additionally, we see a strong positive correlation
between sightline metallicity and low-ion velocity width, the normalization and
slope of which comes close to matching recent observational results. However,
we somewhat underestimate the number of observed high velocity width systems;
the severity of this disagreement is comparable to other recent DLA focused
studies. By z=0 the majority of the z=3 neutral gas forming the DLAs has been
converted into stars, in agreement with rough physical expectations.
[Abridged]
We present photometry of 13 transits of XO-3b, a massive transiting planet on an eccentric orbit. Previous data led to two inconsistent estimates of the planetary radius. Our data strongly favor the smaller radius, with increased precision: R_p = 1.217 +/- 0.073 R_Jup. A conflict remains between the mean stellar density determined from the light curve, and the stellar surface gravity determined from the shapes of spectral lines. We argue the light curve should take precedence, and revise the system parameters accordingly. The planetary radius is about 1 sigma larger than the theoretical radius for a hydrogen-helium planet of the given mass and insolation. To help in planning future observations, we provide refined transit and occultation ephemerides.
Massive black hole binary systems, with masses in the range ~10^4-10^10 \msun, are among the primary sources of gravitational waves in the frequency window ~10^-9 Hz - 0.1 Hz. Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna (LISA) are the observational means by which we will be able to observe gravitational radiation from these systems. We carry out a systematic study of the generation of the stochastic gravitational-wave background from the cosmic population of massive black hole binaries. We consider a wide variety of assembly scenarios and we estimate the range of signal strength in the frequency band accessible to PTAs. We show that, taking into account the uncertainties surrounding the actual key model parameters, the amplitude lies in the interval h_c(f = 10^-8 Hz)~5x10^-16 - 8x10^-15. The most optimistic predictions place the signal level at a factor of ~3 below the current sensitivity of Pulsar Timing Arrays, but within the detection range of the complete Parkes PTA for a wide variety of models, and of the future Square-Kilometer-Array PTA for all the models considered here. We also show that at frequencies >10^-8 Hz the frequency dependency of the generated background follows a power-law significantly steeper than f^-2/3, that has been considered so far. Finally we show that LISA observations of individual resolvable massive black hole binaries are complementary and orthogonal to PTAs observations of a stochastic background from the whole population in the Universe. In fact, the detection of gravitational radiation in both frequency windows will enable us to fully characterise the cosmic history of massive black holes.
We study the alignments between the angular momentum of individual objects
and the large-scale structure in cosmological numerical simulations and real
data from the Sloan Digital Sky Survey, Data Release 6. To this end we measure
anisotropies in the two point cross-correlation function around simulated halos
and observed galaxies, studying separately the 1- and 2-halo regimes. The
alignment of the angular momentum of dark-matter haloes in LCDM simulations is
found to be dependent on scale and halo mass. At large distances (2-halo
regime), the spins of high mass haloes are preferentially oriented in the
direction perpendicular to the distribution of matter; lower mass systems show
a weaker trend that may even reverse to show an angular momentum in the plane
of the matter distribution. In the 1-halo term regime, the angular momentum is
aligned in the direction perpendicular to the matter distribution; the effect
is stronger than for the 1-halo term and increases for higher mass systems.
On the observational side, we focus our study on galaxies in the Sloan
Digital Sky Survey, Data Release 6 (SDSS-DR6) with elongated apparent shapes,
and study alignments with respect to the major semi-axis. We find an excess of
structure in the direction of the major semi-axis for all samples; the red
sample shows the highest alignment (2.7+-0.08%) and indicates that the angular
momentum of flattened spheroidals tends to be perpendicular to the large-scale
structure. (Abridged)
We study the variations of group galaxy properties according to their assembly history in groups identified in the SDSS-DR6 (hereafter SDSS) catalogue. Using mock SDSS group catalogues, we find that the isolation and concentration of a galaxy group are good observational discriminators of group assembly. However, analysing the mean spectral type of SDSS groups as a function of concentration and isolation, we find that while SDSS massive groups confirm the predicted correlation between concentration and age found in mock catalogues, they disagree with models in the isolation-age trend. This may be partially explained in terms of possible problems associated to the modelling of cold gas in satellite galaxies in semi-analytical models, which could be overestimating the effects of environment. We study properties of galaxies in groups of similar masses and different ages, finding important variations between model and observations. These variations can be explained in terms of the different isolation-age trends observed in SDSS and mock groups. In addition to the reported difference in clustering amplitude, groups of similar mass and different assembly history show important differences in their galaxy population. Particularly, the number of members, mass-to-light ratios and red galaxy fractions in SDSS groups show opposite behaviours as the group concetration increases with respect to the trends observed as the isolation increases. Conversely, low mass SDSS groups appear less sensitive to their assembly history.
We point out that a conventional construction placed upon observations of accreting black holes, in which their nonthermal X-ray spectra are produced by inverse comptonization in a coronal plasma, suggests that the plasma is marginally collisionless. Recent developments in plasma physics indicate that fast reconnection takes place only in collisionless plasmas. As has recently been suggested for the Sun's corona, such marginal states may result from a combination of energy balance and the requirements of fast magnetic reconnection.
The luminosity gap between novae (M_R < -10) and supernovae (M_R > -17) is well known since the pioneering research of Zwicky and Hubble. Nearby galaxy clusters and concentrations offer an excellent opportunity to search for explosions brighter than classical novae and fainter than supernovae. Here, we present the results of a B-band survey of 23 member galaxies of the Fornax cluster, performed at the Las Campanas 2.5-m Irene duPont telescope. Observations with a cadence of 32 minutes discovered no genuine fast transient to a limiting absolute magnitude of M_B=-9.3 mag. We provide a detailed assessment of the transient detection efficiency and the resulting upper limits on the event rate as function of peak magnitude. Further, we discuss the discoveries of five previously unknown foreground variables which we identified as two flare stars, two W Uma type eclipsing binaries and a candidate delta Scuti/SX Phe star.
In order to understand the formation and subsequent evolution of galaxies one must first distinguish between the two main morphological classes of massive systems: spirals and early-type systems. This paper introduces a project, Galaxy Zoo, which provides visual morphological classifications for nearly one million galaxies, extracted from the Sloan Digital Sky Survey (SDSS). This achievement was made possible by inviting the general public to visually inspect and classify these galaxies via the internet. The project has obtained more than 40,000,000 individual classifications made by ~100,000 participants. We discuss the motivation and strategy for this project, and detail how the classifications were performed and processed. We find that Galaxy Zoo results are consistent with those for subsets of SDSS galaxies classified by professional astronomers, thus demonstrating that our data provides a robust morphological catalogue. Obtaining morphologies by direct visual inspection avoids introducing biases associated with proxies for morphology such as colour, concentration or structual parameters. In addition, this catalogue can be used to directly compare SDSS morphologies with older data sets. The colour--magnitude diagrams for each morphological class are shown, and we illustrate how these distributions differ from those inferred using colour alone as a proxy for morphology.
In the inflationary cosmology it occurs frequently that the inflaton field is trapped in a local, transient minimum with non-zero vacuum energy. The difficulty regarding the curvature perturbation produced during such a stage is that classically the inflaton does not move so that the comoving hypersurfaces are not well defined at linear order in the scalar field perturbation. In this paper, assuming a mechanism of trapping which resembles a high temperature correction to the potential, we explicitly calculate for the first time the resulting power spectrum of the curvature perturbation by evaluating the quantum two-point correlation function directly. The spectrum is steeply blue with the spectral index n_R = 4.
A mid-infrared (3.6-8 um) survey of the Galactic Center has been carried out with the IRAC instrument on the Spitzer Space Telescope. This survey covers the central 2x1.4 degree (~280x200 pc) of the Galaxy. At 3.6 and 4.5 um the emission is dominated by stellar sources, the fainter ones merging into an unresolved background. At 5.8 and 8 um the stellar sources are fainter, and large-scale diffuse emission from the ISM of the Galaxy's central molecular zone becomes prominent. The survey reveals that the 8 to 5.8 um color of the ISM emission is highly uniform across the surveyed region. This uniform color is consistent with a flat extinction law and emission from polycyclic aromatic hydrocarbons (PAHs). Models indicate that this broadband color should not be expected to change if the incident radiation field heating the dust and PAHs is <10^4 times that of the solar neighborhood. The few regions with unusually red emission are areas where the PAHs are underabundant and the radiation field is locally strong enough to heat large dust grains to produce significant 8 um emission. These red regions include compact H II regions, Sgr B1, and wider regions around the Arches and Quintuplet Clusters. In these regions the radiation field is >10^4 times that of the solar neighborhood. Other regions of very red emission indicate cases where thick dust clouds obscure deeply embedded objects or very early stages of star formation.
We present molecular line observations of the massive star forming region IRAS 17233-3606 aimed at studying the molecular core associated with the source. The observations were made using the Atacama Pathfinder Experiment telescope in the CO (3-2) and HCO^+ (4-3) transitions, and in the CH_3OH (6_K-5_K), (7_K-6_K) and CH_3CN (16_K-15_K) bands. For the CO(3-2) and HCO^+ (4-3) transitions, we obtained maps with a size of 70''\times 70''. The typical angular resolution of the data is ~18''. Our observations reveal an exceptionally rich molecular spectrum, a signpost of hot core activity. Comparisons with two other prominent southern hot cores were made through observations in the same frequency setups. We also detected a bipolar outflow in CO (3-2) and HCO^+ (4-3) lines. Modelling reveals a hot core of size ~3'' and a temperature of 150 K in the IRAS17233-3606 region. The parameters of the molecular outflow are derived through the analysis of the CO (3-2) emission, and are typical of outflows driven by high-mass young stellar objects.
Most of the first-discovered extrasolar multi-planet systems were found to lie close to dynamically unstable configurations. However a few observed multi-planet systems (e.g. HD 74156) did not show this trait. Those systems could share this property if they contain an additional planet in between those that are known. Previous investigations identified the properties of hypothetical planets that would place these systems near instability. The hypothetical planet in HD 74156 was expected to have a mass about equal to that of Saturn, a semi-major axis between 0.9 and 1.4 AU, and an eccentricity less than 0.2. HD 74156 d, a planet with a mass of 1.3 Saturn masses at 1.04 AU with an eccentricity of 0.25, was recently announced. We have reanalyzed all published data on this system in order to place tighter constraints on the properties of the new planet. We find two possible orbits for this planet, one close to that already identified and another (with a slightly better fit to the data) at ~0.89 AU. We also review the current status of other planet predictions, discuss the observed single planet systems, and suggest other systems which may contain planets in between those that are already known. The confirmation of the existence of HD 74156 d suggests that planet formation is an efficient process, and planetary systems should typically contain many planets.
We measure the evolution of the luminous red galaxy (LRG) luminosity function in the redshift range 0.1<z<0.9 using samples of galaxies from the Sloan Digital Sky Survey as well as new spectroscopy of high-redshift massive red galaxies. Our high-redshift sample of galaxies is largest spectroscopic sample of massive red galaxies at z~0.9 collected to date and covers 7 square deg, minimizing the impact of large scale structure on our results. We find that the LRG population has evolved little beyond the passive fading of its stellar populations since z~0.9. Based on our luminosity function measurements and assuming a non-evolving Salpeter stellar initial mass function, we find that the most massive (L>3L*) red galaxies have grown by less than 50% (at 99% confidence), since z=0.9, in stark contrast to the factor of 2-4 growth observed in the L* red galaxy population over the same epoch. We also investigate the evolution of the average LRG spectrum since z~0.9 and find the high-redshift composite to be well-described as a passively evolving example of the composite galaxy observed at low-redshift. From spectral fits to the composite spectra, we find at most 5% of the stellar mass in massive red galaxies may have formed within 1Gyr of z=0.9. While L* red galaxies are clearly assembled at z<1, 3L* galaxies appear to be largely in place and evolve little beyond the passive evolution of their stellar populations over the last half of cosmic history.
The Per OB1 association, which contains the remarkable double cluster h and chi Per, is unusual in not having a giant molecular cloud in its vicinity. We show from Hipparcos data that the luminous members of this association exhibits a bulk motion away from the galactic plane, such that their average velocity increases with height above the galactic plane. We find HAeBe and T Tauri stars towards probable remnant molecular clouds associated with Per OB1. These star-forming regions lie well beyond the location of the luminous member stars at heights of 280-400 pc above the galactic plane, far higher than that previously found for embedded clusters. We argue that the observed motion of the luminous member stars is most naturally explained if many formed from molecular gas pushed and accelerated outwards by an expanding superbubble driven presumably by stellar winds and perhaps also supernova explosions. A large shell of atomic hydrogen gas and dust that lies just beyond the remnant molecular clouds, believed to be driven by just such a superbubble, may comprise the swept-up remains of the parental giant molecular cloud from which this association formed. In support of this picture, we find a week trend for the younger O star members to lie at higher galactic latitudes than the older supergiant members. The star-forming regions located at even larger heights above the galactic plane presumably correspond to more recent episodes of star formation at or near the periphery of this superbubble.
The binary fraction among extreme horizontal branch (EHB) stars in Galactic globular clusters (GCs) is much lower than that among their counterparts, field hot subdwarfs, by an order of magnitude. This casts serious doubt on their formation channels. In the Letter, I explain the difference between the field and the cluster EHB stars with the binary model of Han et al. (2002, 2003) for the formation of EHB stars. With the binary population synthesis code of Han et al. (2002, 2003), I follow the evolution of simple stellar populations resulting from single star bursts (Note that Han et al. (2002, 2003) adopted a constant star formation rate over the last 15 Gyr for the production of field EHB stars), and obtain EHB stars at different stellar population ages. I found that the binary fraction among EHB stars decreases with the stellar population age. The fraction of EHB binaries with orbital periods $P<5 {\rm d}$ is $\sim 2.5%$ for a stellar population of 10 Gyr from the standard simulation set. The binary model of Han et al. (2002, 2003) is able to explain the lack of EHB binaries in globular clusters. I also propose that precise determination of the physical parameters of close EHB binaries in GCs can lead to the strictest constraint on the common-envelope ejection efficiency.
The combined PSF of the BFI and the SOT onboard the Hinode spacecraft is investigated. Observations of the Mercury transit from November 2006 and the solar eclipse(s) from 2007 are used to determine the PSFs of SOT for the blue, green, and red continuum channels of the BFI. For each channel large grids of theoretical point spread functions are calculated by convolution of the ideal diffraction-limited PSF and Voigt profiles. These PSFs are applied to artificial images of an eclipse and a Mercury transit. The comparison of the resulting artificial intensity profiles across the terminator and the corresponding observed profiles yields a quality measure for each case. The optimum PSF for each observed image is indicated by the best fit. The observed images of the Mercury transit and the eclipses exhibit a clear proportional relation between the residual intensity and the overall light level in the telescope. In addition there is a anisotropic stray-light contribution. ... BFI/SOT operate close to the diffraction limit and have only a rather small stray-light contribution. The FWHM of the PSF is broadened by only ~1% with respect to the diffraction-limited case, while the overall Strehl ratio is ~ 0.8. In view of the large variations -- best seen in the residual intensities of eclipse images -- and the dependence on the overall light level and position in the FOV, a range of PSFs should be considered instead of a single PSF per wavelength. The individual PSFs of that range allow then the determination of error margins for the quantity under investigation. Nevertheless the stray-light contributions are here found to be best matched with Voigt functions with the parameters sigma = 0."008 and gamma = 0."004, 0."005, and 0."006 for the blue, green, and red continuum channels, respectively.
We present the results of new high resolution ATCA observations of SNR J0519-6926. We found that this SNR exhibits a typical "horseshoe" appearance with alpha = -0.55 +- 0.08 and D=28+-1 pc. No polarization (or magnetic fields) are detected to a level of 1%. This is probably due to a relatively poor sampling of the uv plane caused be observing in "snap-shot" mode.
We present preliminary results from spectral observations of four candidate radio sources co-identified with known planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). These were made using the Radcliffe 1.9-meter telescope in Sutherland, South Africa. These radio PNe were originally found in Australia Telescope Compact Array (ATCA) surveys of the SMC at 1.42 and 2.37 GHz, and were further confirmed by new high resolution ATCA images at 6 and 3 cm (4"/2"). Optical PNe and radio candidates are within 2" and may represent a subpopulation of selected radio bright objects. Nebular ionized masses of these objects may be 2.6 MSol or greater, supporting the existence of PNe progenitor central stars with masses up to 8 MSol.
This is initial study of a gene signatures responsible for adapting microscopic life to the life in extreme Earth environments. We present a results on ID of the clusters of COGs common to several hyperthermophiles and exclusion of those common to a mesophile: E.coli.K12, will yield a group of proteins possibly involved in adaptation to life under extreme T. Methanogens stand out as the only group of organisms that have species capable of growth at 0C (M.frigidum and M.burtonii) and 110C (M.kandleri). Not all the components of heat adaptation can be attributed to novel genes, the chaperones known as heat shock proteins stabilize the enzymes under elevated temperature. Highly conserved chaperons found in bacteria and eukaryots are not present in hyperthermophilic Archea, rather, they have a unique chaperone TF55. Our aim is to use software which we specifically developed for extremophile genome comparative analyses in order to search for additional novel genes involved in hyperthermophile adaptation. The following hyperthermophile genomes incorporated in our software were used for these studies: M.jannaschii, M.kandleri, A.fulgidus and 3 species of Pyrococcus. Common genes were annotated and grouped according to their roles in cellular processes when information was available and proteins not previously implicated in the heat-adaptation of hyperthermophiles were identified. Additional experimental data is needed in order to learn more about these proteins. To address a non-gene based components of thermal adaptation, all sequenced extremophiles were analysed for their GC contents and aminoacid hydrophobicity. We develop a prediction model for optimal growth temperature.
We study the disc planet interactions of low-mass protoplanets embedded in a circumstellar disc. We extend the standard theory of planet migration from the usual locally isothermal assumption to include non-barotropic effects, focusing on the validity of linear theory. We compared solutions of the linear equations with results from non-linear hydrodynamic simulations, where in both cases we adopted a background entropy gradient and solved the energy equation. We show that the migration behavior of embedded planets depends critically on the background radial entropy gradient in the disc. The presence of such a gradient not only changes the corotation torque on the planet, but also always guarantees a departure from linear behavior, which gives a singular density response at corotation, in the absence of thermal or viscous diffusion. A negative entropy gradient tends to give rise to positive, non-linear corotation torques apparently produced as material executes horseshoe turns at approximately constant entropy. These torques have no counterpart in linear theory, but can be strong enough to push the planet outwards until saturation starts to occur after a horseshoe libration period. Increased thermal diffusion acts to reduce these non-linear torques, but, at the same time, it can help to prevent their saturation. In combination with a small kinematic viscosity that is able to maintain a smooth density profile the positive torque could be sustained.
It is known that the gas has a fractal structure in a wide range of spatial scales with a fractal dimension that seems to be a constant around Df = 2.7. It is expected that stars forming from this fractal medium exhibit similar fractal patterns. Here we address this issue by quantifying the degree to which star-forming events are clumped. We develop, test, and apply a precise and accurate technique to calculate the correlation dimension Dc of the distribution of HII regions in a sample of disk galaxies. We find that the determination of Dc is limited by the number of HII regions, since if there are < 100 regions available then a bias tending to underestimate the dimension is produced. The reliable results are distributed in the range 1.5 < Dc < 2.0 with an average value Dc = 1.81. This corresponds to a three-dimensional dimension of Df = 2.73, very similar to the value measured in the interstellar clouds. However, we get significant variations in the fractal dimension among galaxies, contrary to a universal picture sometimes claimed in literature. The fractal dimension exhibits a weak but significant correlation with the absolute magnitude and, to a lesser extent, with the galactic radius. The faintest galaxies tend to distribute their HII regions in more clustered (less uniform) patterns. The fractal dimension for the brightest HII regions within the same galaxy seems to be smaller than for the faintest ones suggesting some kind of evolutionary efffect, but the obtained correlation remains unchanged if only the brightest regions are taken into account.
We use archival Spitzer Space Telescope photometry of the old, super-solar metallicity massive open cluster NGC 6791 to look for evidence of enhanced mass loss, which has been postulated to explain the optical luminosity function and low white dwarf masses in this benchmark cluster. We find a conspicuous lack of evidence for prolificacy of circumstellar dust production that would have been expected to accompany such mass loss. We also construct the optical and infrared luminosity functions, and demonstrate that these fully agree with theoretical expectations. We thus conclude that there is no evidence for the mass loss of super-solar metallicity red giants to be sufficiently high that they can avoid the helium flash at the tip of the red giant branch.
Recent observations of the Small Magellanic Cloud (SMC) have revealed that the HI gas shows a significant amount of rotation (V_c 60 km/s), while no or little rotation is evident for the old stellar populations. We suggest that this unique kinematical difference between these components in the SMC can be caused by a major merger event which occurred in the early stage of the SMC formation. Our simulations show that dissipative dwarf-dwarf merging can transform two gas-rich dwarf irregulars into a new dwarf, which consists of a spheroidal stellar component and a rotating extended HI disk. The remnant of this dwarf-dwarf merging shows significantly different kinematics between stars and gas, in the sense that a gas disk rotates rapidly while a stellar component shows little rotation. We thus suggest that the simulated dwarf having a dynamically hot spheroid and an extended gas disk finally evolves into the present SMC after efficient stripping of the outer gas via tidal fields of the Galaxy and the Large Magellanic Cloud. We also suggest that spatial distributions and kinematics of RGB and AGB stars with different ages in the possible spheroidal component of the SMC can provide valuable information on whether and when a past major merger event really occurred in the SMC.
The VVDS-Wide survey has been designed with the general aim of tracing the large-scale distribution of galaxies at z~1 on comoving scales reaching ~100Mpc/h, while providing a good control of cosmic variance over areas as large as a few square degrees. This is achieved by measuring redshifts with VIMOS at the ESO VLT to a limiting magnitude I_AB=22.5, targeting four independent fields with size up to 4 sq.deg. each. The whole survey covers 8.6 sq.deg., here we present the general properties of the current redshift sample. This includes 32734 spectra in the four regions (19977 galaxies, 304 type I AGNs, and 9913 stars), covering a total area of 6.1 sq.deg, with a sampling rate of 22 to 24%. The redshift success rate is above 90% independently of magnitude. It is the currently largest area coverage among redshift surveys reaching z~1. We give the mean N(z) distribution averaged over 6.1 sq.deg. Comparing galaxy densities from the four fields shows that in a redshift bin Deltaz=0.1 at z~1 one still has factor-of-two variations over areas as large as ~0.25 sq.deg. This level of cosmic variance agrees with that obtained by integrating the galaxy two-point correlation function estimated from the F22 field alone, and is also in fairly good statistical agreement with that predicted by the Millennium mocks. The variance estimated over the survey fields shows explicitly how clustering results from deep surveys of even ~1 sq.deg. size should be interpreted with caution. This paper accompanies the public release of the first 18143 redshifts of the VVDS-Wide survey from the 4 sq.deg. contiguous area of the F22 field at RA=22h, publicly available at this http URL
We present a new numerical code which solves the general relativistic magneto-hydrodynamics (GRMHD) equations coupled to the Einstein equations for the evolution of a dynamical spacetime. This code has been developed with the main objective of studying astrophysical scenarios in which both, high magnetic fields and strong gravitational fields appear, such as the magneto-rotational collapse of stellar cores, the collapsar model of GRBs, and the evolution of neutron stars. The code is based on an existing and thoroughly tested purely hydrodynamics code and on its extension to accommodate weakly magnetized fluids (passive magnetic field approximation). The numerical code we present here is based on high-resolution shock-capturing schemes to solve the GRMHD equations together with the flux constraint transport method to ensure the solenoidal condition of the magnetic field. Since the astrophysical applications envisaged do not deviate much from spherical symmetry, the conformal flatness condition approximation is used for the formulation of the Einstein equations. In addition, the code can handle several equations of state, from simple analytical expressions to microphysical tabulated ones. In this paper we present stringent tests of our new GRMHD numerical code, which show its ability to handle all aspects appearing in the astrophysical scenarios for which the code is intended, namely relativistic shocks, highly magnetized fluids, and equilibrium configurations of magnetized neutron stars. As an application, magneto-rotational core collapse simulations of a realistic progenitor are presented, comparing the results with our previous finding in the passive magnetic field approximation.
(ABRIDGED) Studies of debris disks have shown that most systems are analogous to the Edgeworth-Kuiper Belt. However a rare subset of sun-like stars possess dust which lies in the terrestrial planet region. In this study we aim to determine how many sources with apparent mid-IR excess are truly hosts of warm dust, and investigate where the dust must lie. We observed using mid-IR imaging with TIMMI2, VISIR and MICHELLE a sample of FGK main sequence stars reported to have hot dust. A new modelling approach was developed to determine the constraints that can be set on the radial extent of excess emission. We confirm the presence of warm dust around 3 of the candidates (eta Corvi, HD145263 and HD202406), and present constraints on the emitting dust regions. Of 2 alternative models for the eta Corvi excess emission, we find that a model with 1 hot dust component at <3 AU (combined with the known submm dust population) fits the data better at the 2.6sigma level than an alternative model with 2 populations of dust in the mid-IR. We identify several systems which have a companion (HD65277 and HD79873) or background object (HD53246, HD123356 and HD128400) responsible for their mid-infrared excess, and for 3 other systems we were able to rule out a point-like source near the star at the level of excess observed in lower resolution observations (HD12039, HD69830 and HD191089). Hot dust sources are either young and possibly primordial or transitional, or have relatively small radius steady-state planetesimal belts, or they are old and luminous with transient emission. High resolution imaging can be used to constrain the location of the disk and help to discriminate between different models of disk emission. For some small disks, interferometry is needed to resolve the disk location.
The pointing directions of extensive air showers observed at the Pierre Auger Observatory were fitted within 3.1 degree with positions of the nearby active galactic nuclei from the Veron-Cetty and P. Veron catalog. The cosmic ray luminosity of the active galactic nuclei which happened to be a source of the particular cosmic ray event constitutes a fraction ~0.0001 of the optical one if only cosmic ray particles with energies above 60 EeV are produced. If produced cosmic ray particles have a spectrum dE/E^3 up to ~100 GeV then the cosmic ray luminosity would be much higher than the optical one of the active galactic nuclei.
We present SDSSJ092712.65+294344.0 as the best candidate to date for a recoiling supermassive black hole (SMBH). SDSSJ0927+2943 shows an exceptional optical emission-line spectrum with two sets of emission lines: one set of very narrow emission lines, and a second set of broad Balmer and broad high-ionization forbidden lines which are blueshifted by 2650 km\s relative to the set of narrow emission lines. This observation is most naturally explained if the SMBH was ejected from the core of the galaxy, carrying with it the broad-line gas while leaving behind the bulk of the narrow-line gas. We show that the observed properties of SDSSJ0927+2943 are consistent with predictions and expectations from recent numerical relativity simulations which demonstrate that SMBHs can receive kicks up to several thousand km\s due to anisotropic emission of gravitational waves during the coalescence of a binary. Our detection of a strong candidate for a rapidly recoiling SMBH implies that kicks large enough to remove SMBHs completely from their host galaxies do occur, with important implications for models of black hole and galaxy assembly at the epoch of structure formation, and for recoil models.
The origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. "Cosmic Magnetism" has been accepted as Key Science Project both for the Low Frequency Array (LOFAR, under construction) and the planned Square Kilometre Array (SKA). At low frequencies LOFAR and SKA will allow to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. High-resolution polarization observations at high frequencies with the SKA will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures (RM) towards polarized background sources will be used to model the structure and strength of the magnetic fields in the Milky Way, the interstellar medium of galaxies and the intergalactic medium. The new method of "RM Synthesis", applied to spectro-polarimetric data cubes, will separate RM components from different distances and allow 3-D "Faraday tomography". Magnetic fields in distant galaxies and clusters and in intergalactic filaments will be searched for by deep imaging of weak synchrotron emission and of RM towards background sources. This will open a new era in the observation of cosmic magnetic fields.
The scenario of gravitino dark matter with broken R-parity naturally reconciles three paradigms that, albeit very well motivated separately, seem to be in mutual conflict: supersymmetric dark matter, thermal leptogenesis and standard Big Bang nucleosynthesis. Interestingly enough, the products of the gravitino decay could be observed, opening the possibility of indirect detection of gravitino dark matter. In this paper, we compute the positron and the antiproton fluxes from gravitino decay. We find that a gravitino with a mass of 150 GeV and a lifetime of 10^26 s could simultaneously explain the EGRET anomaly in the extragalactic diffuse gamma ray background and the HEAT excess in the positron fraction. However, the predicted antiproton flux tends to be too large, although the prediction suffers from large uncertainties and might be compatible with present observations for certain choices of propagation parameters.
In a study of the radio emission mechanism of the FR-I AGN NGC 5128 (Centaurus A)}, we have determined the centimeter and millimeter continuum spectrum of the whole Centaurus A radio source and measured the continuum emission from the active galxy nucleus at various times between 1989 and 2005 at frequencies between 86 GHz (3.5 mm) and 345 GHz (0.85 mm). The integral Cen A spectrum becomes steeper at frequencies above 5 GHz, where the spectral index changes from -0.70 to -0.82. Millimeter emission from the core of Centaurus A is variable, and correlates appreciably better with the 20-200 keV than the 2 - 10 keV X-ray variability. In its quiescent state, the core spectral index is -0.3, which steepens when the core brightens. The variability appears to be mostly associated with the inner nuclear jet components that have been detected in VLBI measurements. The densest nuclear components are optically thick below 45-80 GHz.
We study SN1987A neutrino events through a likelihood analysis with one-component (cooling) and two-component (accretion and cooling) emission model. We show that there is a 3.2 sigma hint for the initial accretion phase.
A population of unidentified gamma-ray sources is forming a structure resembling a halo around the Galactic center. These sources are highly variable, and hence they should be associated with compact objects. Microquasars are objects undergoing accretion with relativistic jets; if such an object has a low-mass, evolved, donor star, it might be found in the Galactic halo. If these low-mass microquasars can generate detectable gamma-ray emission, then they are natural candidates to account for the halo high-energy sources. We aim to construct models for high-energy emission of low-mass microquasars, which could produce a significant luminosity in the gamma-ray domain. We consider that a significant fraction of the relativistic particles in the jets of low-mass microquasars are protons and then we study the production of high-energy emission through proton synchrotron radiation and photopion production. Photopair production and leptonic processes are considered as well. We compute a number of specific models with different parameters to explore the possibilities of this scenario.} We find that important luminosities, in the range of $10^{34}-10^{37}$ erg s$^{-1}$, can be achieved by proton synchrotron radiation in the Gamma-Ray Large Area Space Telescope (GLAST) energy range, and lower, but still significant luminosities at higher energies for some models. We conclude that the "proton microquasar" model offers a very interesting alternative to account for the halo gamma-ray sources and presents a variety of predictions that might be tested in the near future by instruments like GLAST, the High-Energy Stereoscopic System II (HESS II), the Major Atmospheric Gamma-ray Imaging Cherenkov telescope II (MAGIC II), and neutrino telescopes like IceCube.
The autocorrelation function provides an objective test for the existence of special scales in the hierarchical clustering of young stars. We apply this measure to single-star photometry for the brightest main sequence stars in the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC), M33, and M31, using data from the Magellanic Clouds Photometric Survey and the Massey Local Group Survey. Our primary result is the identification of a transition to a higher correlation dimension (weaker clustering) at one kpc in the LMC and M31, and at 300 pc in M33. We suggest that this transition marks the large-scale regime where disk geometry and dynamics set the scale for structure. On smaller scales, the correlation functions for each galaxy are scale-free over at least two orders of magnitude, with a projected correlation dimension varying from 1.0 for M31 to 1.8 for the SMC. This variation is probably caused by a combination of differences in stellar ages and masses, physical environment, and extinction.
Aims. We attempt to detect starlight reflected from a hot Jupiter, orbiting
the main-sequence star HD 75289Ab. We report a revised analysis of observations
of this planetary system presented previously by another research group.
Methods. We analyse high-precision, high-resolution spectra, collected over
four nights using UVES at the VLT/UT2, by way of data synthesis. We try to
interpret our data using different atmospheric models for hot Jupiters.
Results. We do not find any evidence for reflected light, and, therefore,
establish revised upper limits to the planet-to-star flux ratio at the 99.9%
significance level. At high orbital inclinations, where the best sensitivity is
attained, we can limit the relative reflected radiation to be less than e = 6.7
x 10-5 assuming a grey albedo, and e = 8.3 x 10-5 assuming an Class IV
function, respectively. This implies a geometric albedo smaller than p = 0.46
and p = 0.57, for the grey albedo and the Class IV albedo shape, respectively,
assuming a planetary radius of 1.2 RJup.
We present the results of daily monitoring of 6.7 GHz methanol maser in Cepheus A (Cep A) using Yamaguchi 32-m radio telescope as well as the results of imaging observations conducted with the JVN (Japanese VLBI Network). We indentified five spectral features, which are grouped into red-shifted (-1.9 and -2.7 km/s) and blue-shifted (-3.8, -4.2, and -4.9 km/s), and we detected rapid variabilities of these maser features within a monitoring period of 81 days. The red-shifted features decreased in flux density to 50% of its initial value, while the flux density of the blue-shifted features rapidly increased within a 30 days. The time variation of these maser features showed two remarkable properties; synchronization and anti-correlation between the red-shifted and the blue-shifted. The spatial distribution of the maser spots obtained by the JVN observation showed an arclike structure with a scale of $\sim$1400 AU, and separations of the five maser features were found to be larger than 100 AU. The absolute position of the methanol maser was also obtained based on the phase-referencing observations, and the arclike structure were found to be associated with the Cep A-HW2 object, with the elongation of the arclike structure nearly perpendicularly to the radio continuum jet from the Cep A-HW2 object. These properties of the masers, namely, the synchronization of flux variation, and the spectral and spatial isolation of features, suggest that the collisional excitation by shock wave from a common exciting source is unlikely. Instead, the synchronized time variation of the masers can be explained if all the maser features are excited by infrared radiation from dust which is heated by a common exciting source with a rapid variability.
In this study we show how hydrogen and helium lines modelling can be used to make a diagnostic of active and eruptive prominences. One motivation for this work is to identify the physical conditions during prominence activation and eruption. Hydrogen and helium lines are key in probing different parts of the prominence structure and inferring the plasma parameters. However, the interpretation of observations, being either spectroscopic or obtained with imaging, is not straightforward. Their resonance lines are optically thick, and the prominence plasma is out of local thermodynamic equilibrium due to the strong incident radiation coming from the solar disk. In view of the shift of the incident radiation occurring when the prominence plasma flows radially, it is essential to take into account velocity fields in the prominence diagnostic. Therefore we need to investigate the effects of the radial motion of the prominence plasma on hydrogen and helium lines. The method that we use is the resolution of the radiative transfer problem in the hydrogen and helium lines out of local thermodynamic equilibrium. We study the variation of the computed integrated intensities in H and He lines with the radial velocity of the prominence plasma. We can confirm that there exist suitable lines which can be used to make a diagnostic of the plasma in active and eruptive prominences in the presence of velocity fields.
We have begun a survey of the chemical and dynamical properties of the Milky Way disk as traced by open star clusters. In this first contribution, the general goals of our survey are outlined and the strengths and limitations of using star clusters as a Galactic disk tracer sample are discussed. We also present medium resolution (R ~ 15,0000) spectroscopy of open cluster stars obtained with the Hydra multi-object spectrographs on the Cerro Tololo Inter-American Observatory 4-m and WIYN 3.5-m telescopes. Here we use these data to determine the radial velocities of 3436 stars in the fields of open clusters within about 3 kpc, with specific attention to stars having proper motions in the Tycho-2 catalog. Additional radial velocity members (without Tycho-2 proper motions) that can be used for future studies of these clusters were also identified. The radial velocities, proper motions, and the angular distance of the stars from cluster center are used to derive cluster membership probabilities for stars in each cluster field using a non-parametric approach, and the cluster members so-identified are used, in turn, to derive the reliable bulk three-dimensional motion for 66 of 71 targeted open clusters. The high probability cluster members that we identify help to clarify the color-magnitude sequences for many of the clusters, and are prime targets for future echelle resolution spectroscopy as well as astrometric study with the Space Interferometry Mission (SIM Planetquest).
The advent of affordable parallel computers such as Beowulf PC clusters and, more recently, of multi-core PCs has been highly beneficial for a large number of scientists and smaller institutions that might not otherwise have access to substantial computing facilities. However, there has not been an analogous progress in the development and dissemination of parallel software: scientists need the expertise to develop parallel codes and have to invest a significant amount of time in the development of tools even for the most common data analysis tasks. We describe the Beowulf Analysis Symbolic INterface (BASIN) a multi-user parallel data analysis and visualization framework. BASIN is aimed at providing scientists with a suite of parallel libraries for astrophysical data analysis along with general tools for data distribution and parallel operations on distributed data to allow them to easily develop new parallel libraries for their specific tasks.
Magnetic fields are important at every scale in the star formation process: from the dynamics of the ISM in galaxies, to the collapse of turbulent molecular clouds to form stars and in the fragmentation of individual star forming cores. The recent development of a robust algorithm for MHD in the Smoothed Particle Hydrodynamics method has enabled us to perform simulations of star formation including magnetic fields at each of these scales. This paper focusses on three questions in particular: What is the effect of magnetic fields on fragmentation in star forming cores? How do magnetic fields affect the collapse of turbulent molecular clouds to form stars? and: What effect do magnetic fields have on the dynamics of the interstellar medium?
The Delta-variance analysis, has proven to be an efficient and accurate
method of characterising the power spectrum of interstellar turbulence. The
implementation presently in use, however, has several shortcomings.
We propose and test an improved Delta-variance algorithm for two-dimensional
data sets, which is applicable to maps with variable error bars and which can
be quickly computed in Fourier space. We calibrate the spatial resolution of
the Delta-variance spectra.
The new Delta-variance algorithm is based on an appropriate filtering of the
data in Fourier space. It allows us to distinguish the influence of variable
noise from the actual small-scale structure in the maps and it helps for
dealing with the boundary problem in non-periodic and/or irregularly bounded
maps. We try several wavelets and test their spatial sensitivity using
artificial maps with well known structure sizes.
It turns out that different wavelets show different strengths with respect to
detecting characteristic structures and spectral indices, i.e. different
aspects of map structures. As a reasonable universal compromise for the optimum
Delta-variance filter, we propose the Mexican-hat filter with a ratio between
the diameters of the core and the annulus of 1.5.
The Gaia mission will provide an unprecedented 3D view of our galaxy, it will obtain astrometric, photometric and spectrographic data for roughly one billion stars. We are particularly interested in the treasure chest of new data Gaia will produce for hot subdwarf B (sdB) stars. In order for Gaia to classify sdBs and estimate parameters model spectra covering a wide parameter range are needed. Here we describe the construction of an extensive grid, which will be used for this purpose.
Weak lensing analysis is applied to a deep, one square degree r-band CFHT-Megacam image of the Abell 2163 field. The observed shear is fitted with Single Isothermal Sphere and Navarro-Frenk-White models to obtain the velocity dispersion and the mass, respectively; in addition, aperture densitometry is also used to provide a mass estimate at different distances from the cluster centre. The luminosity function is finally derived, allowing to estimate the mass/luminosity ratio. Previous weak lensing analyses performed at smaller scales produced somewhat contradictory results. The mass and velocity dispersion obtained in the present paper are compared and found to be in good agreement with the values computed by other authors from X-ray and spectroscopic data.
There is a clear scarcity of structural parameters for stellar thick discs, especially for spiral galaxies located in high-density regions, such as galaxy clusters and compact groups. We have modelled the thin and thick discs of 4 edge-on spirals located in Abell clusters: NGC 705, ESO243G49, ESO187G19, LCSBS0496P. Deep I band images of NGC 705 were taken from the HST archive, whereas the remaining images were obtained with the Southern Telescope for Astrophysical Research (SOAR) in Gunn r filter. They reached surface brightness levels of $\mu_I \simeq 26.0$ mag arcsec$^{-2}$ and $\mu_r \simeq 26.5$ mag arcsec$^{-2}$, respectively. Profiles were extracted from the deep images, in directions both parallel and perpendicular to the major axis. Profile fits were carried out at several positions, yielding horizontal and vertical scale parameters for both thin and thick disc components. The extracted profiles and fitted disc parameters vary from galaxy to galaxy. Two galaxies have a horizontal profile with a strong down-turn at outer radii, preventing a simple exponential from fitting the entire range. For the 2 early-type spirals, the thick discs have larger scalelengths than the thin discs, whereas no trend is seen for the later types . Both the thin and thick discs sampled tend to have similar scalelengths and scaleheights when compared to typical field disc galaxies. However, the thin disc parameters of the 2 farthest galaxies, both late-type spirals, may be significantly affected by seeing effects. Taken at face value, our results suggest that environment plays a minor role in determining the thin and thick disc sizes.
We present Spitzer observations of IC 443 obtained with MIPS and IRS as part of our GTO program on the astrophysics of ejecta from evolved stars. We find that the overall morphology at mid/far IR wavelengths resembles even more closely a loop or a shell than the ground based optical and/or near IR images.The dust temperature map, based on the 70/160micron ratio, shows a range from 18 to 30 K degrees. The IRS spectra confirm the findings from previous near+mid IR spectroscopic observations of a collisionally excited gas, atomic and molecular, rich in fine structure atomic and pure H2 rotational emission lines, respectively. The spectroscopic shock indicator, [Ne II] 12.8micron, suggests shock velocities ranging from 60-90 km/s, consistent with the values derived from other indicators.
We report measurements of eight native (i.e., released directly from the comet nucleus) volatiles (H2O, HCN, CH4, C2H2, C2H6, CO, H2CO, and CH3OH) in comet 8P/Tuttle using NIRSPEC at Keck 2. Comet Tuttle reveals a truly unusual composition, distinct from that of any comet observed to date at infrared wavelengths. The prominent enrichment of methanol relative to water contrasts the depletions of other molecules, especially C2H2 and HCN. We suggest that the nucleus of 8P/Tuttle may contain two cometesimals characterized by distinct volatile composition. The relative abundances C2/CN, C2/OH, and CN/OH in 8P/Tuttle (measured at optical/near-UV wavelengths) differ substantially from the mixing ratios of their potential parents (C2H2/HCN, C2H2/H2O, and HCN/H2O) found in this work. Based on this comparison, our results do not support C2H2 and HCN being the principal precursors for respectively C2 and CN in Tuttle. The peculiar native composition observed in 8P/Tuttle (compared to other comets) provides new strong evidence for chemical diversity in the volatile materials stored in comet nuclei. We discuss the implications of this diversity for expected variations in the deuterium enrichment of water among comets.
It is now well established that stellar winds of hot stars are fragmentary and that the X-ray emission from stellar winds has a strong contribution from shocks in winds. Chandra high spectral resolution observations of line profiles of O and B stars have shown numerous properties that had not been expected. Here we suggest explanations by considering the X-rays as arising from bow shocks that occur where the stellar wind impacts on spherical clumps in the winds. We use an accurate and stable numerical hydrodynamical code to obtain steady-state physical conditions for the temperature and density structure in a bow shock. We use these solutions plus analytic approximations to interpret some major X-ray features: the simple power-law distribution of the observed emission measure derived from many hot star X-ray spectra and the wide range of ionization stages that appear to be present in X-ray sources throughout the winds. Also associated with the adiabatic cooling of the gas around a clump is a significant transverse velocity for the hot plasma flow around the clumps, and this can help to understand anomalies associated with observed line widths, and the differences in widths seen in stars with high and low mass-loss rates. The differences between bow shocks and the planar shocks that are often used for hot stars are discussed. We introduce an ``on the shock'' (OTSh) approximation that is useful for interpreting the X-rays and the consequences of clumps in hot star winds and elsewhere in astronomy.
Two first order strongly hyperbolic formulations of scalar-tensor theories of gravity (STT) allowing nonminimal couplings (Jordan frame) are presented along the lines of the 3+1 decomposition of spacetime. One is based on the Bona-Masso formulation while the other one employs a conformal decomposition similar to that of Baumgarte-Shapiro-Shibata-Nakamura. A modified Bona-Masso slicing condition adapted to the scalar-tensor theory is proposed for the analysis. This study confirms that the scalar-tensor theory posses a well posed Cauchy problem even when formulated in the Jordan frame.
There exist several prescriptions for identifying the notion of temperature in special relativity. We argue that the inverse temperature 4-vector $\bf B$ is the only viable option from the Second Law of thermodynamics. Using a superfluidity thought experiment, one can show that $\bf B$ is a future-directed timelike 4-vector, and it is not necessarily along the time direction of the comoving frame of the system, as is usually thought. For an isolated system, the 4-vector is determined by its energy-momentum and from the entropy-maximum principle.
We investigate the interaction of the light with propagating axial torsion fields in the presence of an external magnetic field. Axial torsion fields appearing in higher derivative quantum gravity possess two states with spin one and zero with different masses. The torsion field with spin-0 state is a ghost that can interact with the light in the same manner as an axion. The light mixes with torsion fields resulting in the effect of vacuum birefringence and dichroism. From the PVLAS experimental data, we find bounds on a coupling constant of the light-torsion interaction and the mass of the spin-1 state of the torsion field when the mass of the ghost approaches to infinity.
The methods of effective field theory are used to study generic theories of inflation with a single inflaton field. For scalar modes, the leading corrections to the ${\cal R}$ correlation function are found to be purely of the $k$-inflation type. For tensor modes the leading corrections to the correlation function arise from terms in the action that are quadratic in the curvature, including a parity-violating term that makes the propagation of these modes depend on their helicity. These methods are also briefly applied to non-generic theories of inflation with an extra shift symmetry, as in so-called ghost inflation.
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Galactic winds are a prime suspect for the metal enrichment of the intergalactic medium and may have a strong influence on the chemical evolution of galaxies and the nature of QSO absorption line systems. We use a sample of 1406 galaxy spectra at z~1.4 from the DEEP2 redshift survey to show that blueshifted Mg II 2796, 2803 A absorption is ubiquitous in starforming galaxies at this epoch. This is the first detection of frequent outflowing galactic winds at z~1. The presence and depth of absorption are independent of AGN spectral signatures or galaxy morphology; major mergers are not a prerequisite for driving a galactic wind from massive galaxies. Outflows are found in coadded spectra of galaxies spanning a range of 30x in stellar mass and 10x in star formation rate (SFR), calibrated from K-band and from MIPS IR fluxes. The outflows have column densities of order N_H ~ 10^20 cm^-2 and characteristic velocities of ~ 300-500 km/sec, with absorption seen out to 1000 km/sec in the most massive, highest SFR galaxies. The velocities suggest that the outflowing gas can escape into the IGM and that massive galaxies can produce cosmologically and chemically significant outflows. Both the Mg II equivalent width and the outflow velocity are larger for galaxies of higher stellar mass and SFR, with V_wind ~ SFR^0.3, similar to the scaling in low redshift IR-luminous galaxies. The high frequency of outflows in the star-forming galaxy population at z~1 indicates that galactic winds occur in the progenitors of massive spirals as well as those of ellipticals. The increase of outflow velocity with mass and SFR constrains theoretical models of galaxy evolution that include feedback from galactic winds, and may favor momentum-driven models for the wind physics.
By numerically integrating the orbits of the giant planets and of test particles for four billion years, we follow the evolution of the location of the midplane of the Kuiper belt. The Classical Kuiper belt conforms to a warped sheet that precesses with a 1.9 Myr period. The present-day location of the Kuiper belt plane can be computed using linear secular perturbation theory: the local normal to the plane is given by the theory's forced inclination vector, which is specific to every semi-major axis. The Kuiper belt plane does not coincide with the invariable plane, but deviates from it by up to a few degrees in stable zones. A Kuiper belt object keeps its free inclination relative to the Kuiper belt plane nearly constant, even while the plane departs from the trajectory predicted by linear theory. The constancy of free inclination simply reflects the undamped amplitude of free oscillation. Current observations of Classical Kuiper belt objects are consistent with the plane being warped by the giant planets alone, but the sample size will need to increase by a few times before confirmation exceeds 3-sigma in confidence. In principle, differences between the theoretically expected plane and the observed plane could be used to infer as yet unseen masses orbiting the Sun, but carrying out such a program would be challenging.
We study the radial distribution of supernova Ia (SNe Ia) in morphologically selected early-type host galaxies from the Sloan Digital Sky Survey (SDSS) and discuss its implications for the progenitor systems of SNe Ia. While new observations of early-type galaxies suggest that they contain small fractions of young stellar populations, they are also the most likely hosts for long time delay SNe Ia. We find that there is no statistically significant difference between the radial distribution of SNe Ia and the light profile of their early-type host galaxies, which are dominated by old, metal-rich stellar populations. This confirms the commonly accepted idea that some SN Ia progenitors have time delays of the order of several Gyr.
Our main objective is to develop a denoising strategy to increase the signal
to noise ratio of individual spectral lines of stellar spectropolarimetric
observations.
We use a multivariate statistics technique called Principal Component
Analysis. The cross-product matrix of the observations is diagonalized to
obtain the eigenvectors in which the original observations can be developed.
This basis is such that the first eigenvectors contain the greatest variance.
Assuming that the noise is uncorrelated a denoising is possible by
reconstructing the data with a truncated basis. We propose a method to identify
the number of eigenvectors for an efficient noise filtering.
Numerical simulations are used to demonstrate that an important increase of
the signal to noise ratio per spectral line is possible using PCA denoising
techniques. It can be also applied for detection of magnetic fields in stellar
atmospheres. We analyze the relation between PCA and commonly used well-known
techniques like line addition and least-squares deconvolution. Moreover, PCA is
very robust and easy to compute.
In numerical models of thin astrophysical disks that use an Eulerian scheme, gas orbits supersonically through a fixed grid. As a result the time step is sharply limited by the Courant condition. Also, because the mean flow speed with respect to the grid varies with position, the truncation error varies systematically with position. For hydrodynamic (unmagnetized) disks an algorithm called FARGO has been developed that advects the gas along its mean orbit using a separate interpolation substep. This relaxes the constraint imposed by the Courant condition, which now depends only on the peculiar velocity of the gas, and results in a truncation error that is more nearly independent of position. This paper describes a FARGO-like algorithm suitable for evolving magnetized disks. Our method is second order accurate on a smooth flow and preserves the divergence-free constraint to machine precision. The main restriction is that the magnetic field must be discretized on a staggered mesh. We give a detailed description of an implementation of the code and demonstrate that it produces the expected results on linear and nonlinear problems. We also point out how the scheme might be generalized to make the integration of other supersonic/super-fast flows more efficient. Although our scheme reduces the variation of truncation error with position, it does not eliminate it. We show that the residual position dependence leads to characteristic radial variations in the density over long integrations.
The polarization analysis of the light is typically carried out using modulation schemes. The light of unknown polarization state is passed through a set of known modulation optics and a detector is used to measure the total intensity passing the system. The modulation optics is modified several times and, with the aid of such several measurements, the unknown polarization state of the light can be inferred. How to find the optimal demodulation process has been investigated in the past. However, since the modulation matrix has to be measured for a given instrument and the optical elements can present problems of repeatability, some uncertainty is present in the elements of the modulation matrix and/or covariances between these elements. We analyze in detail this issue, presenting analytical formulae for calculating the covariance matrix produced by the propagation of such uncertainties on the demodulation matrix, on the inferred Stokes parameters and on the efficiency of the modulation process. We demonstrate that, even if the covariance matrix of the modulation matrix is diagonal, the covariance matrix of the demodulation matrix is, in general, non-diagonal because matrix inversion is a nonlinear operation. This propagates through the demodulation process and induces correlations on the inferred Stokes parameters.
The presence of nearby discrete cosmic-ray (CR) sources can lead to many interesting effects on the observed properties of CRs. In this paper, we study about the possible effects on the CR primary and secondary spectra and also the subsequent effects on the CR secondary-to-primary ratios. For the study, we assume that CRs undergo diffusive propagation in the Galaxy and we neglect the effect of convection, energy losses and reacceleration. In our model, we assume that there exists a uniform and continuous distribution of CR sources in the Galaxy generating a stationary CR background at the Earth. In addition, we also consider the existence of some nearby sources which inject CRs in a discrete space-time model. Assuming a constant CR source power throughout the Galaxy, our study has found that the presence of nearby supernova remnants (SNRs) produces noticeable variations in the primary fluxes mainly above ~ 100 GeV/n, if CRs are assumed to be released instantaneously after the supernova explosion. The variation reaches a value of ~ 45% at around 10^5 GeV/n. Respect to earlier studies, the variation in the case of the secondaries is found to be almost negligible. We also discuss about the possible effects of the different particle release times from the SNRs. For the particle release time of ~ 10^5 yr, predicted by the diffusive shock acceleration theories in SNRs, we have found that the presence of the nearby SNRs hardly produces any significant effects on the CRs at the Earth.
We present new B, V and R linear polarimetric observations for 61 stars towards the region of the young open cluster NGC 654. In this study we found evidence for the presence of at least two layers of dust along the line of sight to the cluster. The distances to the two dust layers are estimated to be ~ 200 pc and ~ 1 kpc which are located much closer to the Sun than the cluster (~ 2.4 kpc). Both the dust layers have their local magnetic field orientation nearly parallel to the direction of the Galactic plane. The foreground dust layer is found to have a ring morphology with the central hole coinciding with the center of the cluster. The foreground dust grains are suggested to be mainly responsible for both the observed differential reddening and the polarization towards the cluster.
We observed molecular hydrogen around a sample of pre-main sequence stars in order to better characterize their gaseous CS environments. We analyzed the FUSE (Far Ultraviolet Spectroscopic Explorer) spectra of a sample of Herbig Ae/Be stars (HAeBes) covering a broad spectral range, including the main-sequence A5 star Beta-Pictoris. To better diagnose the origin of the detected H2 and its excitation conditions, we used a model of a photodissociation region. Our analysis demonstrates that the excitation of H2 is clearly different around most of the HAeBes compared to the interstellar medium. Moreover, the characteristics of H2 around Herbig Ae and Be stars give evidence for different excitation mechanisms. For the most massive stars of our sample (B8 to B2 type), the excitation diagrams are reproduced well by a model of photodissociation regions (PDR). Our results favor an interpretation in terms of large CS envelopes, remnants of the molecular clouds in which the stars were formed. On the other hand, the group of Ae stars (later than B9 type) known to possess disks is more inhomogeneous. In most cases, when CS H2 is detected, the lines of sight do not pass through the disks. The excitation conditions of H2 around Ae stars cannot be reproduced by PDR models and correspond to warm and/or hot excited media very close to the stars. In addition, no clear correlation has been found between the ages of the stars and the amount of circumstellar H2. Our results suggest structural differences between Herbig Ae and Be star environments. Herbig Be stars do evolve faster than Ae stars, and consequently, most Herbig Be stars are younger than Ae ones at the time we observe them. It is thus more likely to find remnants of their parent cloud around them.
Classical novae are expected to emit gamma rays during their explosions. The most important contribution to the early gamma-ray emission comes from the annihilation with electrons of the positrons generated by the decay of 13N and 18F. The photons are expected to be down-scattered to a few tens of keV, and the emission is predicted to occur some days before the visual discovery and to last ~2 days. Despite a number of attempts, no positive detections of such emission have been made, due to lack of sensitivity and of sky coverage. Because of its huge field of view, good sensitivity, and well-adapted energy band, Swift/BAT offers a new opportunity for such searches. BAT data can be retrospectively used to search for prompt gamma-ray emission from the direction of novae after their optical discovery. We have estimated the expected success rate for the detection with BAT of gamma rays from classical novae using a Monte Carlo approach. Searches were performed for emission from novae occurring since the launch of Swift. Using the actual observing program during the first 2.3 years of BAT operations as an example, and sensitivity achieved, we estimate the expected rate of detection of classical novae with BAT as ~0.2-0.5/yr, implying that several should be seen within a 10 yr mission. The search for emission in the directions of the 24 classical novae discovered since the Swift launch yielded no positive results, but none of these was known to be close enough for this to be a surprise. Detections of a recurrent nova (RS Oph) and a nearby dwarf nova (V455 And) demonstrate the efficacy of the technique. The absence of detections is consistent with the expectations from the Monte Carlo simulations, but the long-term prospects are encouraging given an anticipated Swift operating lifetime of ~10 years.
We have identified 335 galaxy cluster and group candidates, 106 of which are at z > 1, using a 4.5 um selected sample of objects from a 7.25 deg^2 region in the Spitzer Infrared Array Camera (IRAC) Shallow Survey. Clusters were identified as 3-dimensional overdensities using a wavelet algorithm, based on photometric redshift probability distributions derived from IRAC and NOAO Deep Wide-Field Survey data. We estimate only ~10% of the detections are spurious. To date 12 of the z > 1 candidates have been confirmed spectroscopically, at redshifts from 1.06 to 1.41. Velocity dispersions of ~750 km/s for two of these argue for total cluster masses well above 10^14 M_sun, as does the mass estimated from the rest frame near infrared stellar luminosity. Although not selected to contain a red sequence, some evidence for red sequences is present in the spectroscopically confirmed clusters, and brighter galaxies are systematically redder than the mean galaxy color in clusters at all redshifts. The mean I - [3.6] color for cluster galaxies up to z ~ 1 is well matched by a passively evolving model in which stars are formed in a 0.1 Gyr burst starting at redshift z_f = 3. At z > 1, a wider range of formation histories is needed, but higher formation redshifts (i.e. z_f > 3) are favored for most clusters.
Direction measurement of weakly interacting massive particles in time-projection chambers can provide definite evidence of their existence and help to determine their properties. This article demonstrates several concepts for charge amplification in time-projection chambers that can be used in direction-sensitive dark matter search experiments. We demonstrate reconstruction of the 'head-tail' effect for nuclear recoils above 100keV, and discuss the detector performance in the context of dark matter detection and scaling to large detector volumes.
Aims: We derive the 3-D HI volume density distribution for the Galactic disk out to R = 60 kpc. Methods: Our analysis is based on parameters for the warp and rotation curve derived previously. The data are taken from the Leiden/Argentine/Bonn all sky 21-cm line survey. Results: The Milky Way HI disk is significantly warped but shows a coherent structure out to R = 35 kpc. The radial surface density distribution, the densities in the middle of the warped plane, and the HI scale heights all follow exponential relations. The radial scale length for the surface density distribution of the HI disk is 3.75 kpc. Gas at the outskirts for 40 < R < 60 kpc is described best by a distribution with an exponential radial scale length of 7.5 kpc and a velocity dispersion of 74 km/s. Such a highly turbulent medium fits also well with the average shape of the high velocity profile wings observed at high latitudes. The turbulent pressure gradient of such extra-planar gas is on average in balance with the gravitational forces. About 10% of the Milky Way HI gas is in this state. The large scale HI distribution is lopsided; for R < 15 kpc there is more gas in the south. The HI flaring indicates that this asymmetry is caused by a dark matter wake, located at R = 25 kpc in direction of the Magellanic System. Conclusions: The HI disk is made up of two major components. Most prominent is the normal HI disk which can be traced to R = 35 kpc. This is surrounded by a patchy distribution of highly turbulent gas reaching large scale heights but also large radial distances. At the position of the Sun the exponential scale height in the z direction is 3.9 kpc. This component resembles the anomalous gas discovered previously in some galaxies.
Silicon carbide, a refractory material, condenses near the photospheres of C-rich AGB stars, giving rise to a conspicuous emission feature at 11.3 mu. In the presence of a stellar wind, the SiC grains are carried outwards to colder regions, where less refractory carbonaceous material can condense, either by itself or in mantles upon SiC grains. Enough carbon can condense on the latter that their specific feature is completely veiled. Thus may be explained a) the coexistence of the SiC feature protruding above a carbonaceous continuum, with a range of contrasts, corresponding to various volume ratios of mantle to core; b) the ultimate disappearance of the 11.3-$\mu$m feature from the interstellar medium, where the mantle has become completely opaque due to the much higher cosmic abundance of carbon.
We obtain an expression for the energy of the density wave propagating in a multicomponent gravitating medium in the form well known from electrodynamics. Using the above, the possibility of "triple production" of the quasi-particles, or waves, with their energies summing up to zero, in a non-equilibrium medium is demonstrated. That kind of resonance wave interaction is shown to result in the development of an explosion instability. By the method developed in plasma physics, the characteristic time of the instability is evaluated.
We report on the first stereoscopic observations of polar coronal jets made by the EUVI/SECCHI imagers on board the twin STEREO spacecraft. The significantly separated viewpoints ($\sim$ 11$^\circ$) allowed us to infer the 3D dynamics and morphology of a well-defined EUV coronal jet for the first time. Triangulations of the jet's location in simultaneous image pairs led to the true 3D position and thereby its kinematics. Initially the jet ascends slowly at $\approx$10-20 $\mathrm{{km} {s}^{-1}}$ and then, after an apparent 'jump' takes place, it accelerates impulsively to velocities exceeding 300 $\mathrm{{km} {s}^{-1}}$ with accelerations exceeding the solar gravity. Helical structure is the most important geometrical feature of the jet which shows evidence of untwisting. The jet structure appears strikingly different from each of the two STEREO viewpoints: face-on in the one viewpoint and edge-on in the other. This provides conclusive evidence that the observed helical structure is real and is not resulting from possible projection effects of single viewpoint observations. The clear demonstration of twisted structure in polar jets compares favorably with synthetic images from a recent MHD simulation of jets invoking magnetic untwisting as their driving mechanism. Therefore, the latter can be considered as a viable mechanism for the initiation of polar jets.
[Abridged] We detect three robust (plus one less certain) z-dropout sources in two separate fields of our UDF05 HST NICMOS images. These z~7 Lyman-Break Galaxy (LBG) candidates allow us to constrain the Luminosity Function (LF) of the star forming galaxy population at those epochs. By assuming a change in only M* and adopting a linear evolution in redshift, anchored to the measured values at z~6, the best fit evolution coefficient is found to be 0.43+-0.19 mag per unit redshift (0.36+-0.18, if including all four candidates), which provides a value of M*(z=7.2)=-19.7+-0.3. This implies a steady evolution for the LBG LF out to z~7, at the same rate that is observed throughout the z~3 to 6 period. This puts a strong constraint on the star-formation histories of z~6 galaxies, whose ensemble star-formation rate density must be lower by a factor 2 at ~170 Myr before the epoch at which they are observed. In particular, a large fraction of stars in the z~6 LBG population must form at redshifts well above z~7. Extrapolating this steady evolution of the LF out to higher redshifts, we estimate that galaxies would be able to reionize the universe by z~6, provided that the faint-end slope of the z>7 LF steepens to alpha~-1.9, and that faint galaxies, with luminosities below the current detection limits, contribute a substantial fraction of the required ionizing photons. This scenario gives however an integrated optical depth to electron scattering that is ~2sigma below the WMAP-5 measurement. Therefore, altogether, our results indicate that, should galaxies be the primary contributors to reionization, either the currently detected evolution of the galaxy population slows down at z>7, or the LF evolution must be compensated by a decrease in metallicity and a corresponding increase in ionization efficiency at these early epochs.
The Delta-variance analysis is an efficient tool for measuring the structural
scaling behaviour of interstellar turbulence in astronomical maps. In paper I
we proposed essential improvements to the Delta-variance analysis.
In this paper we apply the improved Delta-variance analysis to i) a
hydrodynamic turbulence simulation with prominent density and velocity
structures, ii) an observed intensity map of rho Oph with irregular boundaries
and variable uncertainties of the different data points, and iii) a map of the
turbulent velocity structure in the Polaris Flare affected by the intensity
dependence on the centroid velocity determination.
The tests confirm the extended capabilities of the improved Delta-variance
analysis. Prominent spatial scales were accurately identified and artifacts
from a variable reliability of the data were removed. The analysis of the
hydrodynamic simulations showed that the injection of a turbulent velocity
structure creates the most prominent density structures are produced on a scale
somewhat below the injection scale. The new analysis of a rho Oph continuum map
reveals an intermediate stage in the molecular cloud evolution showing both
signatures of the typical molecular cloud scaling behaviour and the formation
of condensed cores. When analysing the velocity structure of the Polaris Flare
we show that a universal power law connects scales from 0.03 pc to 3 pc.
However, a plateau in the Delta-variance spectrum around 5 pc indicates that
the visible large-scale velocity gradient is not converted directly into a
turbulent cascade.
The origin of magnetic fields in astrophysical objects is a challenging problem in astrophysics. Throughout the years, many scientists have suggested that non-minimal gravitational-electromagnetic coupling (NMGEC) could be the origin of the ubiquitous astrophysical magnetic fields. We investigate the possible origin of intense magnetic fields $\sim 10^{15}-10^{16}$ by NMGEC near rotating neutron stars and black holes, connected with magnetars, quasars, and gamma-ray bursts. Whereas these intense magnetic fields are difficult to explain astrophysically, we find that they are easily explained by NMGEC.
The hypothesis of quantum nonequilibrium at the big bang is shown to have observable consequences. For a scalar field on expanding space, we show that relaxation to quantum equilibrium (in de Broglie-Bohm theory) is suppressed for field modes whose quantum time evolution satisfies a certain inequality, resulting in a 'freezing' of early quantum nonequilibrium for these particular modes. For an early radiation-dominated expansion, the inequality implies a corresponding physical wavelength that is larger than the (instantaneous) Hubble radius. These results make it possible, for the first time, to make quantitative predictions for nonequilibrium deviations from quantum theory, in the context of specific cosmological models. We discuss some possible consequences: corrections to inflationary predictions for the cosmic microwave background, non-inflationary super-Hubble field correlations, and relic nonequilibrium particles.
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The formation and growth of galaxy disks over cosmic time is crucial to our understanding of galaxy formation. Despite steady improvements in the size and quality of disk samples over the last decade, many aspects of galaxy disk evolution remain unclear. Using two square degrees of deep, wide-field i'-band imaging from the Canada-France-Hawaii Telescope Legacy Survey, we compute size functions for 6000 disks from z=0.2 to z=1 and explore luminosity and number density evolution scenarios with an emphasis on the importance of selection effects on the interpretation of the data. We also compute the size function of a very large sample of disks from the Sloan Digital Sky Survey to use as a local (z ~ 0.1) comparison. CFHTLS size functions computed with the same fixed luminosity-size selection window at all redshifts exhibit evolution that appears to be best modelled by a pure number density evolution. The z = 0.3 size function is an excellent match to the z = 0.9 one if disks at the highest redshift are a factor of 2.5 more abundant than in the local universe. The SDSS size function would also match the z = 0.9 CFHTLS size function very well with a similar change in number density. On the other hand, the CFHTLS size functions computed with a varying luminosity-size selection window with redshift remain constant if the selection window is shifted by 1.0$-$1.5 mag towards fainter magnitudes with decreasing redshift. There is a weak dependence on disk scale length with smaller ($h \lesssim $ 4 kpc) disks requiring more luminosity evolution than larger ones. Given that changes in number density are primarily due to mergers and that current estimates of merger rates below z = 1 are low, luminosity evolution appears to be a more plausible scenario to explain the observations.
Using the Sloan Digital Sky Survey (SDSS) galaxy group catalogue of Yang et al. (2007), we study the average colour and average concentration of satellite galaxies as function of (i) their stellar mass, (ii) their group mass, and (iii) their group-centric radius. We find that the colours and concentrations of satellite galaxies are (almost) completely determined by their stellar mass. In particular, at fixed stellar mass, the average colours and concentrations of satellite galaxies are independent of either halo mass or halo-centric radius. We find clear evidence for mass segregation of satellite galaxies in haloes of all masses, and argue that this explains why satellites at smaller halo-centric radii are somewhat redder and somewhat more concentrated. In addition, the weak colour and concentration dependence of satellite galaxies on halo mass is simply a reflection of the fact that more massive haloes host, on average, more massive satellites. Combining these results with the fact that satellite galaxies are, on average, redder and somewhat more concentrated than central galaxies of the same stellar mass, the following picture emerges: galaxies become redder and somewhat more concentrated once they fall into a bigger halo (i.e., once they become a satellite galaxy). This is a clear manifestation of environment dependence. However, there is no indication that the magnitude of the transformation (or its timescale) depends on environment; a galaxy undergoes a transition when it becomes a satellite, but it does not matter whether it becomes a satellite of a small (Milky Way sized) halo, or of a massive cluster. We discuss the implication of this `dearth' of environment dependence for the physical processes responsible for transforming satellite galaxies.
Poststarburst galaxies exhibit spectroscopic signatures indicating that their star formation was recently quenched; they are candidates for galaxies in transition from a star-forming phase to a passively-evolving phase. We have spectroscopically identified large samples of poststarburst galaxies both in the SDSS survey at z~0.1 and in the DEEP2 survey at z~0.8, using a uniform and robust selection method based on measurements of Hbeta line emission rather than the more problematic [O II]. Based on measurements of the overdensity of galaxies around each object, we find that poststarburst galaxies brighter than L*(B) at both low and high redshifts are preferentially found in underdense environments, a trend similar to but stronger than that for star-forming galaxies. These modest differences in the overdensity distributions of star-forming galaxies and poststarbursts are statistically significant in our z~0.1 sample, but not at z~0.8. The poststarburst fraction among field galaxies in the DEEP2 sample is higher than that among DEEP2 group galaxies with 2.5-sigma significance. We conclude that mergers of gas-rich galaxies in underdense environments or gas heating in dark matter halos with M~10^12 Msun/h are more likely to be the dominant poststarburst formation mechanism than cluster-specific mechanisms such as ram-pressure stripping, galaxy harassment, or strangulation. Given the inability of galaxies to quickly change their environments within 1Gyr, the timescale for poststarburst signatures to disappear and a galaxy to join the red sequence, the fact that the environment distribution of poststarburst galaxies is radically different from that of red galaxies indicates that a poststarburst phase cannot be the only route toward the formation of red, early-type galaxies.
The spectral distributions of Be/X-ray binaries in the Large Magellanic Cloud and Galaxy have been shown to differ significantly from the distribution of isolated Be stars in the Galaxy. Population synthesis models can explain this difference in spectral distributions through substantial angular momentum loss from the binary system. In this work we explore the spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud (SMC) using high signal-to-noise spectroscopy of a sample of 37 optical counterparts to known X-ray pulsars. Our results show that the spectral distribution of Be/X-ray binaries in the SMC is consistent with that of the Galaxy, despite the lower metallicity environment of the SMC. This may indicate that, although the metallicity of the SMC is conducive to the formation of a large number of HMXBs, the spectral distribution of these systems is likely to be most strongly influenced by angular momentum losses during binary evolution, which are not particularly dependent on the local metallicity.
Two families of exact simple solutions of Einstein field equations for inhomogeneous stiff cosmologies are presented. The method to obtain the solutions is based on the introduction of auxiliary functions in order to cast the Einstein equations in such a way that can be explicitly integrated. Now, despite of the equations are mathematically equivalent to the equations obtained when the source of matter is a scalar field, is worth to mention that the source that we consider is not a scalar field but a perfect fluid with the stiff equation of state. The obtained solutions are expressed in terms of simple functions of the used coordinates and two families of particular solutions are considered. The geometrical and kinematical properties of the solutions are then analyzed and the parameters are restricted in order to have a physically acceptable behavior. The two particular solutions are of the Petrov type I, the first one being regular everywhere whereas the second one presents a big-bang singularity. Now, for a particular value of one of the parameters, the second particular solution is a vacuum solution of the Bianchi I type that reduces to the Kasner solution.
Radio observations of gas in the Milky Way and Local Group are vital for understanding how galaxies function as systems. The unique sensitivity of Arecibo's 305m dish, coupled with the 7-beam Arecibo L-Band Feed Array (ALFA), provides an unparalleled tool for investigating the full range of interstellar phenomena traced by the HI 21cm line. The GALFA (Galactic ALFA) HI Survey is mapping the entire Arecibo sky over a velocity range of -700 to +700 km/s with 0.2 km/s velocity channels and an angular resolution of 3.4 arcminutes. We present highlights from the TOGS (Turn on GALFA Survey) portion of GALFA-HI, which is covering thousands of square degrees in commensal drift scan observations with the ALFALFA and AGES extragalactic ALFA surveys. This work is supported in part by the National Astronomy and Ionosphere Center, operated by Cornell University under cooperative agreement with the National Science Foundation.
We carried out an unbiased mapping survey of dense molecular cloud cores traced by the NH3 (1,1) and (2,2) inversion lines in the GF9 filament which contains an extremely young low-mass protostar GF9-2 (Furuya et al. 2006, ApJ, 653, 1369). The survey was conducted using the Nobeyama 45m telescope over a region of ~1.5 deg with an angular resolution of 73". The large-scale map revealed that the filament contains at least 7 dense cores, as well as 3 possible ones, located at regular intervals of ~0.9 pc. Our analysis shows that these cores have kinetic temperatures of $\lesssim$ 10 K and LTE-masses of 1.8 -- 8.2 Msun, making them typical sites of low-mass star formation. All the identified cores are likely to be gravitationally unstable because their LTE-masses are larger than their virial masses. Since the LTE-masses and separations of the cores are consistent with the Jeans masses and lengths, respectively, for the low-density ambient gas, we argue that the identified cores have formed via the gravitational fragmentation of the natal filamentary cloud.
The Optical Monitor Catalogue of serendipitous sources (OMCat) contains
entries for every source detected in the publicly available XMM-Newton Optical
Monitor (OM) images taken in either the imaging or ``fast'' modes. Since the OM
is coaligned and records data simultaneously with the X-ray telescopes on
XMM-Newton, it typically produces images in one or more near-UV/optical bands
for every pointing of the observatory. As of the beginning of 2006, the public
archive had covered roughly 0.5% of the sky in 2950 fields.
The OMCat is not dominated by sources previously undetected at other
wavelengths; the bulk of objects have optical counterparts. However, the OMCat
can be used to extend optical or X-ray spectral energy distributions for known
objects into the ultraviolet, to study at higher angular resolution objects
detected with GALEX, or to find high-Galactic-latitude objects of interest for
UV spectroscopy.
We assess the impact of Galactic synchrotron foreground removal on the observation of high-redshift quasar HII regions in redshifted 21-cm emission. We consider the case where a quasar is observed in an intergalactic medium (IGM) whose ionisation structure evolves slowly relative to the light crossing time of the HII region, as well as the case where the evolution is rapid. The latter case is expected towards the end of the reionisation era where the highest redshift luminous quasars will be observed. In the absence of foregrounds the fraction of neutral hydrogen in the IGM could be measured directly from the contrast between the HII region and surrounding IGM. However, we find that foreground removal lowers the observed contrast between the HII region and the IGM. This indicates that measurement of the neutral fraction would require modelling to correct for this systematic effect. On the other hand, foreground removal does not modify the most prominent features of the 21-cm maps. Using a simple algorithm we demonstrate that measurements of the size and shape of observed HII regions will not be affected by continuum foreground removal. Moreover, measurements of these quantities will not be adversely affected by the presence of a rapidly evolving IGM.
We investigate mechanisms of energy extraction from a rotating black hole in terms of negative energy-at-infinity. In addition to the Penrose process through particle fission, the Blandford-Znajek mechanism by magnetic tension, and the magnetohydrodynamic Penrose process, we examine energy extraction from a black hole caused by magnetic reconnection in the ergosphere. The reconnection redistributes the angular momentum efficiently to yield the negative energy-atinfinity. We derive a condition for the process to operate in a simple situation, where the plasma is incompressible and the magnetic energy is converted completely to the plasma kinetic energy locally. Astrophysical situations of magnetic reconnection around the black holes are also discussed.
The Fokker-Planck (FP) model is one of the commonly used methods for studies of the dynamical evolution of dense spherical stellar systems such as globular clusters and galactic nuclei. The FP model is numerically stable in most cases, but we find that it encounters numerical difficulties rather often when the effects of tidal shocks are included in two-dimensional (energy and angular momentum space) version of the FP model or when the initial condition is extreme (e.g., a very large cluster mass and a small cluster radius). To avoid such a problem, we have developed a new integration scheme for a two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI) method given in the Douglas-Rachford split form. We find that our ADI method reduces the computing time by a factor of ~2 compared to the fully implicit method, and resolves problems of numerical instability.
The reactions of cold H atoms with solid O2 molecules were investigated at 10 K. The formation of H2O2 and H2O has been confirmed by in-situ infrared spectroscopy. We found that the reaction proceeds very efficiently and obtained the effective reaction rates. This is the first clear experimental evidence of the formation of water molecules under conditions mimicking those found in cold interstellar molecular clouds. Based on the experimental results, we discuss the reaction mechanism and astrophysical implications.
Evolution of the mass function (MF) and radial distribution (RD) of the Galactic globular cluster (GC) system is calculated using an advanced and a realistic Fokker-Planck (FP) model that considers dynamical friction, disc/bulge shocks and eccentric cluster orbits. We perform hundreds of FP calculations with different initial cluster conditions, and then search a wide-parameter space for the best-fitting initial GC MF and RD that evolves into the observed present-day Galactic GC MF and RD. By allowing both MF and RD of the initial GC system to vary, which is attempted for the first time in the present Letter, we find that our best-fitting models have a higher peak mass for a lognormal initial MF and a higher cut-off mass for a power-law initial MF than previous estimates, but our initial total masses in GCs, M_{T,i} = 1.5-1.8x10^8 Msun, are comparable to previous results. Significant findings include that our best-fitting lognormal MF shifts downward by 0.35 dex during the period of 13 Gyr, and that our power-law initial MF models well-fit the observed MF and RD only when the initial MF is truncated at >~10^5 Msun. We also find that our results are insensitive to the initial distribution of orbit eccentricity and inclination, but are rather sensitive to the initial concentration of the clusters and to how the initial tidal radius is defined. If the clusters are assumed to be formed at the apocentre while filling the tidal radius there, M_{T,i} can be as high as 6.9x10^8 Msun, which amounts to ~75 per cent of the current mass in the stellar halo.
The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad-hoc manner. Thus no complete and direct comparison with observations of the pulsar population within the Galactic disk has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed \textit{typical} MSP formation process. Results also focus on reproducing the observed $P\dot{P}$ diagram for Galactic pulsars and how this precludes short timescales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass.
We analyze the behaviors of reddening vectors in the SDSS photometric system for galaxies of different morphologies, ages, and redshifts. As seen in other photometric systems, the dependence of reddening on the spectral energy distribution (SED) and the nonlinearity of reddening are likewise non-negligible for the SDSS system if extinction is significant (~> 1 mag). These behaviors are most significant for the g filter, which has the largest bandwidth-to-central wavelength ratio among SDSS filters. The SDSS colors involving adjacent filters show greater SED-dependence and nonlinearity. A procedure for calculating the correct amount of extinction from an observed color excess is provided. The relative extinctions between (i.e., the extinction law for) SDSS filters given by Schlegel et al., which were calculated with an older version of filter response functions, would underestimate the amount of extinction in most cases by ~5 to 10 % (maximum ~20 %). We recommend A/A_{5500} values of 1.574, 1.191, 0.876, 0.671 & 0.486 for the u, g, r, i, & z filters, respectively, as a representative extinction law for the SDSS galaxies with a small extinction (i.e., for cases where the nonlinearity and SED-dependence of the reddening is not important). The dependence of reddening on redshift at low extinction is the largest for colors involving the g filter as well, which is due to the Balmer break.
An order-of-magnitude estimate for the incidence of high-amplitude delta Scuti-type variable stars (HADS) in the delta Scuti area of the H-R diagram is calculated. Using a model for the stellar distribution in the Milky Way, we calculate the number of stars that are expected to fall in the delta Scuti area of the H-R diagram within the magnitude range and sky coverage of the ROTSE Survey for Variables I (RSV1). The incidence of the HADS phenomenon is then obtained by comparing the number of stars calculated by the model and the actual, observed number of HADS in the RSV1. We find that ~0.3 % of the stars that lie in the delta Scuti area of the H-R diagram within the RSV1 observational limits exhibit the HADS phenomenon. This number is much lower than the incidence of the low-amplitude delta Scuti stars (LADS), ~>1/3, implying that the HADS phenomenon takes place in a very small fraction of stars and/or its duration is very short, compared to the LADS.
Periodicity search in gamma-ray data is usually difficult because of the small number of detected photons. A periodicity in the timing signal at other energy bands from the counterpart to the gamma-ray source may help to establish the periodicity in the gamma-ray emission and strengthen the identification of the source in different energy bands. It may, however, still be difficult to find the period directly from X-ray data because of limited exposure. We developed a procedure, by cross-checking two X-ray data sets, to find candidate periods for X-ray sources which are possible counterparts to gamma-ray pulsar candidates. Here we report the results of this method obtained with all the currently available X-ray data of 8 X-ray sources. Some tempting periodicity features were found. Those candidate periods can serve as the target periods for future search when new data become available so that a blind search with a huge number of trials can be avoided.
We study the compression driven magnetic reconnection in the relativistic electron-positron plasma. Making use of a 2.5D particle-in-cell code, we simulated compression of a magnetized plasma layer containing a current sheet within it. We found that the particle spectrum within the reconnecting sheet becomes non-thermal; it could be approximated by a power-law distribution with an index of -1 and an exponential cutoff.
This paper presents a prescription for distilling the information contained in the cosmic microwave background radiation from multiple sky maps that also contain both instrument noise and foreground contaminants. The prescription is well-suited for cosmological parameter estimation and accounts for uncertainties in the cosmic microwave background extraction scheme. The technique is computationally viable at low resolution and may be considered a natural and significant generalization of the "Internal Linear Combination" approach to foreground removal. An important potential application is the analysis of the multi-frequency temperature and polarization data from the forthcoming Planck satellite.
In1879 George Howard Darwin theoretically analyzed the outward spiraling orbit of Moon and the subsequent lengthening of the Mean Solar Day. The author redid the same analysis based on the fact that Moon was receding at the rate of 3.8 cm per annum. Basic Mechanics of Earth-Moon is worked out and various system parameters are optimized to fit the given boundary condition obtained by Apollo Mission and other modern means of observations. Based on this theoretical formulation the theoretical graph of the lengthening of the Mean Solar Day with respect to time is drawn and is compared with the observational graph of the same based on pale ontological data, paleo tidal data and iron-banded formation. The observational data on Mean Solar Day is found to follow the theoretical smooth curve in post-Cambrian Era but is found to deviate in the remote past. This deviation is corrected by taking the evolving form of Moment of Inertia of Earth. The deviation of the observed data prompts the Author to suggest that the lengthening of the Mean Solar Day curve could possibly be used as an analytical seismograph for the impending earthquakes and sudden volcanic eruptions. The Basic Mechanics of E-M system is generalized to lay the foundation of simulation software for any Planet-Satellite pair in our Solar System.
Two different multi-resolution analyses are used to decompose the structure of active region magnetic flux into concentrations of different size scales. Lines separating these opposite polarity regions of flux at each size scale are found. These lines are used as a mask on a map of the magnetic field gradient to sample the local gradient between opposite polarity regions of given scale sizes. It is shown that the maximum, average and standard deviation of the magnetic flux gradient for alpha, beta, beta-gamma and beta-gamma-delta active regions increase in the order listed, and that the order is maintained over all length-scales. This study demonstrates that, on average, the Mt. Wilson classification encodes the notion of activity over all length-scales in the active region, and not just those length-scales at which the strongest flux gradients are found. Further, it is also shown that the average gradients in the field, and the average length-scale at which they occur, also increase in the same order. Finally, there are significant differences in the gradient distribution, between flaring and non-flaring active regions, which are maintained over all length-scales. It is also shown that the average gradient content of active regions that have large flares (GOES class 'M' and above) is larger than that for active regions containing flares of all flare sizes; this difference is also maintained at all length-scales.
Accretion and merger shocks in clusters of galaxies are potential accelerators of high-energy particles. We show that they may provide a significant contribution to cosmic rays above the second knee feature in the spectrum around 10^17.5 eV. Due to pp interactions with the intracluster gas, such cosmic rays would also generate a diffuse background of high-energy neutrinos above PeV that may be detectable by upcoming neutrino telescopes such as IceCube or KM3NeT, offering a crucial test of this proposal, as well as a probe of cosmic-ray confinement properties in clusters.
White dwarfs with surface magnetic fields in excess of $1 $MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables. Some 1,253 white dwarfs with a detached low-mass main-sequence companion are identified in the Sloan Digital Sky Survey but none of these is observed to show evidence for Zeeman splitting of hydrogen lines associated with a magnetic field in excess of 1MG. If such high magnetic fields on white dwarfs result from the isolated evolution of a single star then there should be the same fraction of high field white dwarfs among this SDSS binary sample as among single stars. Thus we deduce that the origin of such high magnetic fields must be intimately tied to the formation of cataclysmic variables. CVs emerge from common envelope evolution as very close but detached binary stars that are then brought together by magnetic braking or gravitational radiation. We propose that the smaller the orbital separation at the end of the common envelope phase, the stronger the magnetic field. The magnetic cataclysmic variables originate from those common envelope systems that almost merge. We propose further that those common envelope systems that do merge are the progenitors of the single high field white dwarfs. Thus all highly magnetic white dwarfs, be they single stars or the components of MCVs, have a binary origin. This hypothesis also accounts for the relative dearth of single white dwarfs with fields of 10,000 - 1,000,000G. Such intermediate-field white dwarfs are found preferentially in cataclysmic variables. In addition the bias towards higher masses for highly magnetic white dwarfs is expected if a fraction of these form when two degenerate cores merge in a common envelope. Similar scenarios may account for very high field neutron stars.
We present high signal-to-noise measurements of the acoustic scale in the presence of nonlinear growth and redshift distortions using 320(Gpc/h)^3 of cosmological PM simulations. Using simple fitting methods, we obtain robust measurements of the acoustic scale with scatter close to that predicted by the Fisher matrix. We detect and quantify the shift in the acoustic scale by analyzing the power spectrum: we detect at greater than 5 sigma a decrease in the acoustic scale in the real-space matter power spectrum of 0.2% at z=1.5, growing to 0.45% at z=0.3. In redshift space, the shifts are about 25% larger: we detect a decrease of 0.25% of at z=1.5 and 0.54% at z=0.3. Despite the nonzero amounts, these shifts are highly predictable numerically, and hence removable within the standard ruler analysis of clustering data. Moreover, we show that a simple density-field reconstruction method substantially reduces the scatter and nonlinear shifts of the acoustic scale measurements: the shifts are reduced to less than 0.1% at z=0.3-1.5, even in the presence of non-negligible shot noise. Finally, we show that the ratio of the cosmological distance to the sound horizon that would be inferred from these fits is robust to variations in the parameterization of the fitting method and reasonable differences in the template cosmology.
In this paper we consider dark matter particles annihilation in the gravitational field of black holes. We obtain exact distribution function of the infalling dark matter particles, and compute the resulting flux and spectra of gamma rays coming from the objects. It is shown that the dark matter density significantly increases near a black hole. Particle collision energy becomes very high affecting on relative cross-sections of various annihilation channels. We also discuss possible experimental consequences of these effects.
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