We have performed a systematic search for X-ray cavities in the hot gas of 51 galaxy groups with Chandra archival data. The cavities are identified based on two methods: subtracting an elliptical beta model fitted to the X-ray surface brightness, and performing unsharp masking. 13 groups in the sample 25% are identified as clearly containing cavities, with another 13 systems showing tentative evidence for such structures. We find tight correlations between the radial and tangential radii of the cavities, and between their size and projected distance from the group center, in quantitative agreement with the case for more massive clusters. This suggests that similar physical processes are responsible for cavity evolution and disruption in systems covering a large range in total mass. We see no clear association between the detection of cavities and the current 1.4 GHz radio luminosity of the central brightest group galaxy, but there is a clear tendency for systems with a cool core to be more likely to harbor detectable cavities. To test the efficiency of the adopted cavity detection procedures, we employ a set of mock images designed to mimic typical Chandra data of our sample, and find that the model-fitting approach is generally more reliable than unsharp masking for recovering cavity properties. Finally, we find that the detectability of cavities is strongly influenced by a few factors, particularly the signal-to-noise ratio of the data, and that the real fraction of X-ray groups with prominent cavities could be substantially larger than the 25--50% suggested by our analysis.
We present a catalog of 105 rich and massive ($M>3\times10^{14}M_{\sun}$) optically-selected clusters of galaxies extracted from 70 square-degrees of public archival griz imaging from the Blanco 4-m telescope acquired over 45 nights between 2005 and 2007. We use the clusters' optically-derived properties to estimate photometric redshifts, optical luminosities, richness, and masses. We complement the optical measurements with archival XMM-Newton and ROSAT X-ray data which provide additional luminosity and mass constraints on a modest fraction of the cluster sample. Two of our clusters show clear evidence for central lensing arcs; one of these has a spectacular large-diameter, nearly-complete Einstein Ring surrounding the brightest cluster galaxy. A strong motivation for this study is to identify the massive clusters that are expected to display prominent signals from the Sunyaev-Zeldovich Effect (SZE) and therefore be detected in the wide-area mm-band surveys being conducted by both the Atacama Cosmology Telescope and the South Pole Telescope. The optical sample presented here will be useful for verifying new SZE cluster candidates from these surveys, for testing the cluster selection function, and for stacking analyzes of the SZE data.
The first phase of stellar evolution in the history of the Universe may be Dark Stars, powered by dark matter heating rather than by nuclear fusion. Weakly Interacting Massive Particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars for millions to billions of years. In this paper we show that these objects can grow to be supermassive dark stars (SMDS) with masses $\gtrsim (10^5-10^7) \msun$. The growth continues as long as dark matter heating persists, since dark stars are large and cool (surface temperature $\lesssim 5\times 10^4$K) and do not emit enough ionizing photons to prevent further accretion of baryons onto the star. The dark matter may be provided by two mechanisms: (1) gravitational attraction of dark matter particles on a variety of orbits not previously considered, and (2) capture of WIMPs due to elastic scattering. Once the dark matter fuel is exhausted, the SMDS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes in the Universe. SMDS are very bright, with luminosities exceeding $(10^9-10^{11}) L_\odot$. We demonstrate that for several reasonable parameters, these objects will be detectable with JWST. Such an observational discovery would confirm the existence of a new phase of stellar evolution powered by dark matter.
Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than ~200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of ~5 over a smooth-halo assumption. We also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. In this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.
We performed observations of NGC1569 for 6 infrared bands (3.2, 4.1, 7, 11,
15, and 24 micron) with the Infrared Camera (IRC) onboard AKARI. Near- to
mid-infrared (2--13 micron) spectroscopy of a Halpha filament was also carried
out with the IRC.
The extended structure associated with a Halpha filament appears bright at 7
micron, suggesting that the filament is bright at the UIR band emission.
Follow-up spectroscopic observations with the IRC confirm the presence of 6.2,
7.7, and 11.3 micron emission in the filament. The filament spectrum exhibits
strong 11.3 micron UIR band emission relative to the 7.7 micron band compared
to the galaxy disk observed with the Infrared Spectrograph on Spitzer. The
near-infrared spectrum also suggests the presence of excess continuum emission
in 2.5--5 micron in the filament.
The Halpha filament is thought to have been formed by the galactic outflow
originating from the star-formation activity in the disk of NGC1569. The
destruction timescale of the UIR band carriers in the outflow is estimated to
be much shorter (~ 1.3 x 10^3 yr) than the timescale of the outflow (~ 5.3
Myr). Thus it is unlikely that the band carriers survive the outflow
environment. Alternatively, we suggest that the band carriers in the filaments
may be produced by the fragmentation of large carbonaceous grains in shocks,
which produces the Halpha emission. The NIR excess continuum emission cannot be
accounted for by free-free emission alone and a hot dust contribution may be
needed, although the free-free emission intensity estimated from HI
recombination lines has a large uncertainty.
In this work we present scanning Fabry-Perot H$\alpha$ observations of the isolated interacting galaxy pair NGC 5278/79 obtained with the PUMA Fabry-Perot interferometer. We derived velocity fields and rotation curves for both galaxies. For NGC 5278 we also obtained the residual velocity map to investigate the non-circular motions, and estimated its mass by fitting the rotation curve with a disk+halo components. We test three different types of halo (pseudo-isothermal, Hernquist and Navarro Frenk White) and obtain satisfactory fits to the rotation curve for all profiles. The amount of dark matter required by pseudo-isothermal profile is about ten times smaller than, that for the other two halo distributions. Finally, our kinematical results together with the analysis of dust lanes distribution and of surface brightness profiles along the minor axis allowed us to determine univocally that both components of the interacting pair are trailing spirals.
We present a new technique to estimate the level of contamination between photometric redshift bins. If the true angular cross-correlation between redshift bins can be safely assumed to be zero, any measured cross-correlation is a result of contamination between the bins. We present the theory for an arbitrary number of redshift bins, and discuss in detail the case of two and three bins which can be easily solved analytically. We use mock catalogues constructed from the Millennium Simulation to test the method, showing that artificial contamination can be successfully recovered with our method. We find that degeneracies in the parameter space prohibit us from solving uniquely for the contamination, though constraints are made which can be improved with larger data sets. We then apply the method to an observational galaxy survey; the deep component of the Canada France Hawaii Telescope Legacy Survey. We estimate the level of contamination between photometric redshift bins and demonstrate our ability to reconstruct both the true redshift distribution and the true average redshift of galaxies in each photometric bin.
[Abridged] Using VLT/FORS2 spectroscopy, we have studied the properties of the central stellar populations of a sample of 38 nucleated early-type dwarf (dE) galaxies in the Virgo Cluster. We find that these galaxies do not exhibit the same average stellar population characteristics for different morphological subclasses. The nucleated galaxies without discs are older and more metal poor than the dEs with discs . The alpha-element abundance ratio appears consistent with the solar value for both morphological types. Besides a well-defined relation of metallicity and luminosity, we also find a clear anti-correlation between age and luminosity. More specifically, there appears to be a bimodality: brighter galaxies, including the discy ones, exhibit significantly younger ages than fainter dEs. Therefore, it appears less likely that fainter and brighter dEs have experienced the same evolutionary history, as the well-established trend of decreasing average stellar age when going from the most luminous ellipticals towards low-luminosity Es and bright dEs is broken here. The older and more metal-poor dEs could have had an early termination of star formation activity, possibly being "primordial" galaxies in the sense that they have formed along with the protocluster or experienced very early infall. By contrast, the younger and relatively metal-rich brighter dEs, most of which have discs, might have undergone structural transformation of infalling disc galaxies.
We studied the formation and evolution of low-mass stars within halos with high concentration of dark matter (DM) particles, using a highly sophisticated expression to calculate the rate at which DM particles are captured inside the star. For very high DM densities in the host halo (\rho_{\chi}>10^10 GeV cm^-3 for a 1 M_{\odot} star), we found that young stars stop sooner their gravitational collapse in the pre-Main Sequence phase, reaching states of equilibrium in which DM annihilation is their only source of energy. The lower effective temperature of these stars, which depends on the properties of the DM particles and DM halo, may be used as an alternative method to investigate the nature of DM.
VLA observations at 1477 MHz revealed the presence of a radio mini-halo surrounding the faint central point-like radio source in the Ophiuchus cluster of galaxies. In this work we present a study of the radio emission from this cluster of galaxies at lower radio frequencies. We observed the Ophiuchus cluster at 153, 240, and 614 MHz with the GMRT. The mini-halo is clearly detected at 153 and 240 MHz while it is not detected at 610 MHz. The most prominent feature at low frequencies is a patch of diffuse steep spectrum emission located at about 5' south-east from the cluster center. By combining these images with that at 1477 MHz, we derived the spectral index of the mini-halo. Globally, the mini-halo has a low-frequency spectral index of alpha_240^153 ~1.4 +/- 0.3 and an high-frequency spectral index of alpha_1477^240 ~ 1.60 +/- 0.05. Moreover, we measure a systematic increase of the high-frequency spectral index with radius: the azimuthal radial average of alpha_1477^240 increases from about 1.3, at the cluster center, up to about 2.0 in the mini-halo outskirts. The observed radio spectral index is in agreement with that obtained by modeling the non-thermal hard X-ray emission in this cluster of galaxies. We assume that the X-ray component arises from inverse Compton scattering between the photons of the cosmic microwave background and a population of non-thermal electrons which are isotropically distributed and whose energy spectrum is a power law with index p. We derive that the electrons energy spectrum should extend from a minimum Lorentz factor of gamma_min < 700 up to a maximum Lorentz factor of gamma_max =3.8 x 10^4 with an index p=3.8 +/- 0.4. The volume-averaged strength for a completely disordered intra-cluster magnetic field is B_V ~0.3 +/- 0.1 micro-G.
We assess the effects of simulated active galactic nuclei (AGNs) on the colour and morphology measurements of their host galaxies. To test the morphology measurements, we select a sample of galaxies not known to host AGNs and add a series of point sources scaled to represent specified fractions of the observed V band light detected from the resulting systems; we then compare morphology measurements of the simulated systems to measurements of the original galaxies. AGN contributions >20 per cent bias most of the morphology measurements tested, though the extent of the apparent bias depends on the morphological characteristics of the original galaxies. We test colour measurements by adding to non-AGN galaxy spectra a quasar spectrum scaled to contribute specified fractions of the rest-frame B band light detected from the resulting systems. A quasar fraction of 5 per cent can move the NUV-r colour of an elliptical galaxy from the UV-optical red sequence to the green valley, and 20 per cent can move it into the blue cloud. Combining the colour and morphology results, we find that a galaxy/AGN system with an AGN contribution >20 per cent may appear bluer and more bulge-dominated than the underlying galaxy. We conclude that (1) bulge-dominated, E/S0/Sa, and early-type morphology classifications are accurate for red AGN host galaxies and may be accurate for blue host galaxies, unless the AGN manifests itself as a well-defined point source; and (2) although highly unobscured AGNs, such as the quasar used for our experiments, can significantly bias the measured colours of AGN host galaxies, it is possible to identify such systems by examining optical images of the hosts for the presence of a point source and/or measuring the level of nuclear obscuration.
(abridged) NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense burst of star formation 10 to 40 Myr ago. We present observations that reach surface brightnesses two to eighty times fainter than previous radio continuum observations and the first radio continuum polarization observations. These observations allow us to probe the relationship of the magnetic field of NGC 1569 to the rest of its interstellar medium. We confirm the presence of an extended radio continuum halo at 20 cm and see for the first time the radio continuum feature associated with the western Halpha arm at wavelengths shorter than 20cm. The spectral index trends in this galaxy support the theory that there is a convective wind at work in this galaxy. We derive a total magnetic field strength of 38 microG in the central regions and 10-15 microG in the halo. The magnetic field is largely random in the center of the galaxy; the uniform field is ~3-9 microG and is strongest in the halo. We find that the magnetic pressure is the same order of magnitude but, in general, a factor of a few less than the other components of the interstellar medium in this galaxy. The uniform magnetic field in NGC 1569 is closely associated with the Halpha bubbles and filaments. We suggest that a supernova-driven dynamo may be operating in this galaxy. The outflow of hot gas from NGC 1569 is clearly shaping the magnetic field, but the magnetic field in turn may be aiding the outflow by channeling gas out of the disk of the galaxy. Dwarf galaxies with extended radio continuum halos like that of NGC 1569 may play an important role in magnetizing the intergalactic medium.
The next generation of weak lensing surveys will trace the growth of large scale perturbations through a sequence of epochs, offering an opportunity to test General Relativity (GR) on cosmological scales. We review in detail the parametrization used in MGCAMB to describe the modified growth expected in alternative theories of gravity and generalized dark energy models. We highlight its advantages and examine several theoretical aspects. In particular, we show that the same set of equations can be consistently used on super-horizon and sub-horizon linear scales. We also emphasize the sensitivity of data to scale-dependent features in the growth pattern, and propose using Principal Component Analysis to converge on a practical set of parameters which is most likely to detect departures from GR. The connection with other parametrizations is also discussed.
We analyze the physical properties and infall rates of the circum-galactic gas around disks obtained in multi-resolved, cosmological, AMR simulations. At intermediate and low redshifts, disks are embedded into an extended, hot, tenuous corona that contributes largely in fueling the disk with non-enriched gas whereas the accretion of enriched gas from tidal streams occurs throughout episodic events. We derive an infall rate close to the disk of the same value as the one of the star formation rate in the disk and its temporal evolution as a function of galacto-centric radius nicely shows that the growth of galactic disks proceeds according to an inside-out formation scenario.
Recently, spatially inhomogeneous cosmological models have been proposed as an alternative to the LCDM model, with the aim of reproducing the late time dynamics of the Universe without introducing a cosmological constant or dark energy. This paper investigates the possibility of distinguishing such models from the standard LCDM using background or large scale structure data. It also illustrates and emphasizes the necessity of testing the Copernican principle in order to confront the tests of general relativity with the large scale structure.
We discuss the primordial spectrum of a massless and minimally coupled scalar field, produced during the initial anisotropic epoch before the onset of inflation. We consider two models of the anisotropic cosmology, the (planar) Kasner de Sitter solution (Bianchi I) and the Taub-NUT de Sitter solution (Bianchi IX), where the 3-space geometry is initially anisotropic, followed by the de Sitter phase due to the presence of a positive cosmological constant. We discuss the behavior of a quantized, massless and minimally coupled scalar field in the anisotropic stage, which is a counterpart of the inflaton fluctuation. The initial condition is set by the requirement that the scalar field is initially in an adiabatic state. In the Kasner de Sitter model, for one branch of planar solutions there is an adiabatic vacuum unless $k_3\neq 0$, where $k_3$ is the comoving momentum along the third direction, while in the other branch there is no adiabatic state. In the first branch, for the moderate modes, $k_3\sim k$, where $k$ is the total comoving momentum, the scalar power spectrum has an oscillatory behavior and its direction dependence is suppressed. For the planar modes, $k_3\ll k$, in contrast, the direction dependence becomes more important, because of the amplification of the scalar amplitude during this interval of the violation of WKB approximation in the initial anisotropic stage. The qualitative behaviors in the Taub-NUT de Sitter models are very similar to the case of the first branch of the planar Kasner de Sitter model.
As the vacuum state of a quantum field is not an eigenstate of the Hamiltonian density, the vacuum energy density can be represented as a random variable. We present an analytical calculation of the probability distribution of the vacuum energy density for real and complex massless scalar fields in Minkowski space. The obtained probability distributions are broad and the vacuum expectation value of the Hamiltonian density is not fully representative of the vacuum energy density.
The Ep,i - Eiso correlation is one of the most intriguing properties of GRBs, with significant implications for the understanding of the physics and geometry of the prompt emission, the identification and investigation of different classes of GRBs, the use of GRBs as cosmological probes. The Fermi satellite, by exploiting the high accuracy of the GBM instrument in the measurement of Ep, the simultaneous detection of GRBs with Swift, and the detection and localization of GRBs in the GeV energy range by the LAT instrument, is allowing us to enrich the sample of of GRBs with known redshift and reliable estimate of Ep,i, and, thus, to further test the robustness, reliability and extension of this correlation. Based on published results and preliminary spectral data available as of the end of 2009, it is found that the locations in the Ep,i - Eiso plane of Fermi long and short GRBs with measured redshift, including extremely energetic events, are consistent with the results provided by previous / other experiments.
To compare photometric properties of galaxies at different redshifts, the fluxes need to be corrected for the changes of effective rest-frame wavelengths of filter bandpasses, called K-corrections. Usual approaches to compute them are based on the template fitting of observed spectral energy distributions (SED) and, thus, require multi-colour photometry. Here, we demonstrate that, in cases of widely used optical and near-infrared filters, K-corrections can be precisely approximated as two-dimensional low-order polynomials of only two parameters: redshift and one observed colour. With this minimalist approach, we present the polynomial fitting functions for K-corrections in SDSS ugriz, UKIRT WFCAM YJHK, Johnson-Cousins UBVR_cI_c, and 2MASS JHK_s bands for galaxies at redshifts Z<0.5 based on empirically-computed values obtained by fitting combined optical-NIR SEDs of a set of 10^5 galaxies constructed from SDSS DR7 and UKIDSS DR5 photometry using the Virtual Observatory. For luminous red galaxies we provide K-corrections as functions of their redshifts only. In two filters, g and r, we validate our solutions by computing K-corrections directly from SDSS DR7 spectra. We also present a K-corrections calculator, a web-based service for computing K-corrections on-line.
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We present the results of a high-spatial-resolution study of the line emission in a sample of z=3.1 Lyman-Alpha-Emitting Galaxies (LAEs) in the Extended Chandra Deep Field-South. Of the eight objects with coverage in our HST/WFPC2 narrow-band imaging, two have clear detections and an additional two are barely detected (~1.5-sigma). The clear detections are within ~0.5 kpc of the centroid of the corresponding rest-UV continuum source, suggesting that the line-emitting gas and young stars in LAEs are spatially coincident. The brightest object exhibits extended emission with a half-light radius of ~1.5 kpc, but a stack of the remaining LAE surface brightness profiles is consistent with the WFPC2 point spread function. This suggests that the Lyman Alpha emission in these objects originates from a compact (<~1.5 kpc) region and cannot be significantly more extended than the far-UV continuum emission (<~1 kpc). Comparing our WFPC2 photometry to previous ground-based measurements of their monochromatic fluxes, we that we cannot be failing to account for more than 23% of the Lyman Alpha emission from the objects in our sample.
We use the mock catalog of galaxies, constructed based on the COSMOS galaxy catalog including information on photometric redshifts (photo-z) and SED types of galaxies, in order to study how to define a galaxy subsample suitable for weak lensing tomography feasible with optical (and NIR) multi-band data. Since most of useful cosmological information arises from the sample variance limited regime for planned lensing surveys, a suitable subsample can be obtained by discarding a large fraction of galaxies that have less reliable photo-z estimations, mostly photo-z outliers. We develop a method to efficiently identify photo-z outliers by monitoring the width of posterior likelihood unction of redshift estimation for each galaxies. By using the Fisher information matrix formalism, we propagate photo-z errors into biases in cosmological parameters, especially dark energy equation of state parameter w. We found that, by discarding most of ill-defined photo-z galaxies, the bias in w may be reduced to the level comparable to the marginalized statistical error, however, the residual, small systematic bias remains due to asymmetric scatters around the relation between photometric and true redshifts. Even so we argue that such a cleaned photo-z subsample may require less stringent requirements on spectroscopic samples to calibrate the residual photo-z errors. We also use the mock catalog to estimate the cumulative signal-to-noise (S/N) ratios for measuring the angular cross-correlations of galaxies between finner photo-z bins, finding the higher S/N values for photo-z bins including photo-z outliers.
Using the Hubble Space Telescope ACS imaging of the GOODS North and South fields during Cycles 11, 12, and 13, we derive empirical constraints on the delay-time distribution function for type Ia supernovae. We extend our previous analysis to the three-year sample of 56 SNe Ia over the range 0.2<z<1.8, using a Markov chain Monte Carlo to determine the best-fit unimodal delay-time distribution function. The test, which ultimately compares the star formation rate density history to the unbinned volumetric SN Ia rate history from the GOODS/HST-SN survey, reveals a SN Ia delay-time distribution that is tightly confined to 3-4 Gyrs (to >95% confidence). This result is difficult to resolve with any intrinsic delay-time distribution function (bimodal or otherwise), in which a substantial fraction (e.g., >10%) of events are ``prompt'', requiring less than approximately 1 Gyr to develop from formation to explosion. The result is, however, strongly motivated by the decline in the number of SNe Ia at z>1.2. Sub-samples of the HST-SN data confined to lower redshifts (z<1) show plausible delay-time distributions that are dominated by prompt events, which is more consistent with results from low-redshift supernova samples and supernova host galaxy properties. Scenarios in which a substantial fraction of z>1.2 supernovae are extraordinarily obscured by dust may partly explain the differences in low-z and high-z results. Other possible resolutions may include environmental dependencies (such as gas-phase metallicity) that affect the progenitor mechanism efficiency, especially in the early universe.
We present a quantitative morphological analysis using HST NICMOS H160- and ACS I775- band imaging of 25 spectroscopically confirmed submillimetre galaxies (SMGs) which have redshifts between z=0.7-3.4. Our analysis also employs a comparison sample of more typical star-forming galaxies at similar redshifts (such as LBGs) which have lower far-infrared luminosities. This is the first large-scale study of the morphologies of SMGs in the near-infrared at ~0.1" resolution (<1kpc). We find that the half light radii of the SMGs (r_h=2.3+/-0.3 and 2.8+/-0.4kpc in the observed I- and H-bands respectively) and asymmetries are not statistically distinct from the comparison sample of star-forming galaxies. However, we demonstrate that the SMG morphologies differ more between the rest-frame UV and optical-bands than typical star-forming galaxies and interpret this as evidence for structured dust obscuration. We show that the composite observed H-band light profile of SMGs is better fit with a Sersic index with n~2, suggesting the stellar structure of SMGs is best described by a spheroid/elliptical galaxy light distribution. We also compare the sizes and stellar masses of SMGs to local and high-redshift populations, and find that the SMGs have stellar densities which are comparable to local early-type galaxies, as well as luminous, red and dense galaxies at z~1.5 which have been proposed as direct SMG descendants, although the SMG stellar masses and sizes are systematically larger. Overall, our results suggest that the physical processes occuring within the galaxies are too complex to be simply characterised by the rest-frame UV/optical morphologies which appear to be essentially decoupled from all other observables, such as bolometric luminosity, stellar or dynamical mass.
We report the first two-dimensional stellar population synthesis in the
near-infrared of the nuclear region of an active galaxy, namely Mrk1066.
We have used integral field spectroscopy with adaptive optics at the Gemini
North Telescope to map the to map the age distribution of the stellar
population in the inner 300 pc at a spatial resolution of 35 pc. An old stellar
population component (age >5Gyr) is dominant within the inner ~160pc, which we
attribute to the galaxy bulge. Beyond this region, up to the borders of the
observation field (~300 pc), intermediate age components (0.3-0.7Gyr) dominate.
We find a spatial correlation between this intermediate age component and a
partial ring of low stellar velocity dispersions (sigma). Low-sigma nuclear
rings have been observed in other active galaxies and our result for Mrk1066
suggests that they are formed by intermediate age stars. This age is consistent
with an origin for the low-sigma rings in a past event which triggered an
inflow of gas and formed stars which still keep the colder kinematics (as
compared to that of the bulge) of the gas from which they have formed. At the
nucleus proper we detect, in addition, two unresolved components: a compact
infrared source, consistent with an origin in hot dust with mass ~1.9x10^{-2}
M_Sun, and a blue featureless power-law continuum, which contributes with only
~15% of the flux at 2.12 microns.
The bar formation is still an open problem in modern astrophysics. In this paper we present numerical simulation performed with the aim of analyzing the growth of the bar instability inside stellar-gaseous disks, where the star formation is triggered, and a central black hole is present. The aim of this paper is to point out the impact of such a central massive black hole on the growth of the bar. We use N-body-SPH simulations of the same isolated disk-to-halo mass systems harboring black holes with different initial masses and different energy feedback on the surrounding gas. We compare the results of these simulations with the one of the same disk without black hole in its center. We make the same comparison (disk with and without black hole) for a stellar disk in a fully cosmological scenario. A stellar bar, lasting 10 Gyrs, is present in all our simulations. The central black hole mass has in general a mild effect on the ellipticity of the bar but it is never able to destroy it. The black holes grow in different way according their initial mass and their feedback efficiency, the final values of the velocity dispersions and of the black hole masses are near to the phenomenological constraints.
We present a simultaneous analysis of 18 galaxy lenses with time delay
measurements. For each lens we derive mass maps using pixelated simultaneous
modeling with shared Hubble constant. We estimate the Hubble constant to be
66_{-4}^{+6} km/s/Mpc (for a flat Universe with \Omega_m=0.3,
\Omega_\Lambda=0.7).
We have also selected a subsample of five relatively isolated early type
galaxies and by simultaneous modeling with an additional constraint on
isothermality of their mass profiles we get H_0=76 +/-3 km/s/Mpc.
A bright feature 80 pc away from the core in the powerful jet of M87 shows highly unusual properties. Earlier radio, optical and X-ray observations have shown that this feature, labeled HST-1, is superluminal, and is possibly connected with the TeV flare detected by HESS in 2005. It has been claimed that this feature might have a blazar nature, due to these properties. To examine the possible blazar-like nature of HST-1, we analyzed lambda 2 cm VLBA archival data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs obtained between 2000 and 2009. Applying VLBI wide-field imaging techniques, the HST-1 region was imaged at milliarcsecond resolution. Here we present the first 2 cm VLBI detection of this feature in observations from early 2003 to early 2007, and analyze its evolution over this time. Using the detections of HST-1, we find that the projected apparent speed is 0.61 +/- 0.31 c. A comparison of the VLA and VLBA flux densities of this feature indicate that is mostly resolved on molliarcsecond scales. This feature is optically thin between lambda 2 cm and lambda 20 cm. We do not find evidence of a blazar nature for HST-1.
We derive a Cardy-Verlinde-like formula which relates the entropy of the closed FRW universe to its energy, and Casimir energy, for a multicomponent coupled fluid. The generalized fluid obeys an inhomogeneous equation of state. A viscous dark fluid is included, and we include also modified gravity using its fluid representation. It is demonstrated how such an expression reduces to the standard Cardy-Verlinde formula corresponding to the 2d CFT entropy only in some special cases. The dynamical entropy bound for a closed FRW universe with dark components is obtained. The universality of the dynamical entropy bound near a future singularity (of all four types), as well as near the Big Bang singularity, is investigated. It is demonstrated that except from some special cases of Type II and Type IV singularities the dynamical entropy bound is violated near the singularity even if quantum effects are taken into account. The dynamical entropy bound seems to be universal for the case of a regular universe, including the asymptotic de Sitter one.
Even if only a small fraction of neutron dipole moments are aligned in a neutron star, observed pulsar radiation loses provide a stringent limit on the neutron electric dipole moment of <10-29 ecm, more stringent than best current experimental limits.
Radially inhomogeneous gamma-ray burst (GRB) jets release variable photospheric emission and can have internal shocks occurring above the photosphere. We argue that the photospheric emission may correspond to the traditional (Band) component at <~1MeV, and the Compton upscattered photospheric (UP) emission off the electrons in the internal shocks may be the distinct high-energy spectral component at >~10MeV, which is observed by Fermi/LAT for some GRBs. We find that a distinct, bright UP emission does not need strong fine tuning of the physical parameters, but the appropriate parameter ranges are limited, which is consistent with the fact that not all the LAT GRBs have a distinct high-energy component. The observed delays of the distinct component behind the Band component which are large compared to the variability times are unlikely to be due to kinematic effects. They may instead be attributed to the temporal evolution of the physical parameters of the jet, and thus the delay timescales could provide a potential tool for investigating the structures of GRB jets themselves and their environments. Based on this idea, we speculate that the difference of the delay timescales of long and short GRBs inferred from the Fermi data could originate from the differences of the progenitors of long and short GRBs. Some other properties of this model are discussed, including temporal correlations among the prompt optical, soft X-ray, and the distinct high-energy component as well as the Band component.
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The existence of submillimeter-selected galaxies (SMGs) at redshifts z>4 has recently been confirmed. Using simultaneously all the available data from UV to radio we have modelled the spectral energy distributions of the six known spectroscopically confirmed SMGs at z>4. We find that their star formation rates (average ~2500 MSun yr^-1), stellar (~3.6x10^11 MSun) and dust (~6.7x10^8 MSun) masses, extinction (A_V~2.2 mag) and gas-to-dust ratios (~60) are within the ranges for 1.7<z<3.6 SMGs. Our analysis suggests that infrared-to-radio luminosity ratios of SMGs do not change up to redshift ~5 and are lower by a factor of ~2.1 than the value corresponding to the local IR-radio correlation. However, we also find dissimilarities between z>4 and lower-redshift SMGs. Those at z>4 tend to be among the most star-forming, least massive and hottest (~60 K) SMGs and exhibit the highest fraction of stellar mass formed in the ongoing starburst (~45%). This indicates that at z>4 we see earlier stages of evolution of submillimeter-bright galaxies. Using the derived properties for z>4 SMGs we investigate the origin of dust at epochs less than 1.5 Gyr after the Big Bang. This is significant to our understanding of the evolution of the early Universe. For three z>4 SMGs asymptotic giant branch stars could be the dominant dust producers. However, for the remaining three only supernovae are efficient and fast enough to be responsible for dust production, though requiring a very high dust yield per supernova (0.15-0.65 MSun). The required dust yields are lower if a top-heavy initial mass function or significant dust growth in the interstellar medium are assumed. We estimate lower limits of the contribution of SMGs to the cosmic star formation and stellar mass densities at z~4-5 to be ~4% and ~1%, respectively.
We present a new and simple technique for selecting extensive, complete and pure quasar samples, based on their intrinsic variability. We parametrize the single-band variability by a power-law model for the light-curve structure function, with amplitude A and power-law index gamma. We show that quasars can be efficiently separated from other non-variable and variable sources by the location of the individual sources in the A-gamma plane. We use ~60 epochs of imaging data, taken over ~5 years, from the SDSS stripe 82 (S82) survey, where extensive spectroscopy provides a reference sample of quasars, to demonstrate the power of variability as a quasar classifier in multi-epoch surveys. For UV-excess selected objects, variability performs just as well as the standard SDSS color selection, identifying quasars with a completeness of 90% and a purity of 95%. In the redshift range 2.5<z<3, where color selection is known to be problematic, variability can select quasars with a completeness of 90% and a purity of 96%. This is a factor of 5-10 times more pure than existing color-selection of quasars in this redshift range. Selecting objects from a broad griz color box without u-band information, variability selection in S82 can afford completeness and purity of 92%, despite a factor of 30 more contaminants than quasars in the color-selected feeder sample. This confirms that the fraction of quasars hidden in the 'stellar locus' of color-space is small. To test variability selection in the context of Pan-STARRS 1 (PS1) we created mock PS1 data by down-sampling the S82 data to just 6 epochs over 3 years. Even with this much sparser time sampling, variability is an encouragingly efficient classifier. For instance, a 92% pure and 44% complete quasar candidate sample is attainable from the above $griz$-selected catalog.
Observational data show that the correlation between supermassive black holes (MBH) and galaxy bulge (Mbulge) masses follows a nearly linear trend, and that the correlation is strongest with the bulge rather than the total stellar mass (Mgal). With increasing redshift, the ratio Gamma=MBH/Mbulge relative to z=0 also seems to be larger for MBH >~ 10^{8.5} Msol. This study looks more closely at statistics to better understand the creation and observations of the MBH-Mbulge correlation. It is possible to show that if galaxy merging statistics can drive the correlation, minor mergers are responsible for causing a *convergence to linearity* most evident at high masses, whereas major mergers have a central limit convergence that more strongly *reduces the scatter*. This statistical reasoning is agnostic about galaxy morphology. Therefore, combining statistical prediction (more major mergers ==> tighter correlation) with observations (bulges = tightest correlation), would lead one to conclude that more major mergers (throughout an entire merger tree, not just the primary branch) give rise to more prominent bulges. With regard to controversial findings that Gamma increases with redshift, this study shows why the luminosity function (LF) bias argument, taken correctly at face value, strengthens rather than weakens the results. However, correcting for LF bias is unwarranted because the BH mass scale for quasars is bootstrapped to the MBH-Sigma* correlation in normal galaxies at z=0, and quasar-quasar comparisons are internally consistent. In Monte-Carlo simulations, high Gamma objects are "under-merged" galaxies that take longer to converge to linearity via minor mergers. Another evidence that the galaxies are undermassive at z >~ 2 for their MBH is that the quasar hosts are very compact for their expected mass.
The Epoch of Reionization (EoR) is the epoch in which hydrogen in the Universe reionize after the "Dark Ages". This is the second of two major phase transitions that hydrogen in the Universe underwent, the first phase being the recombination era in which hydrogen became neutral at redshift about 1100. The EoR, occurs around z of 10 and is probably caused by the first radiation emitting astrophysical sources, hence it is crucial to our understanding of when and how the Universe "decided" to start forming astrophysical objects and how that influenced subsequent structure formation in the Universe. As such, the EoR is related to many fundamental questions in cosmology, galaxy formation, quasars and very metal poor stars; all are foremost research issues in modern astrophysics. The redshifted 21 cm hyperfine line is widely considered as the most promising probe for studying the EoR in detail. In the near future a number of low frequency radio telescopes (LOFAR, MWA, GMRT and SKA) will be able to observe the 21 cm radiation arriving from the high redshift Universe. In this paper I present our current picture of the ionization process, review the 21 cm line physics and discuss the challenges that the current generation experiments are expected to face. Finally, I discuss the potential of SKA in exploring the EoR and the Universe's Dark Ages.
Many barred galaxies harbor small-scale secondary bars in the center. The evolution of such double-barred galaxies is still not well understood, partly because of a lack of realistic N-body models with which to study them. Here we report the generation of such systems in the presence of rotating pseudobulges. We demonstrate with high mass and force resolution collisionless N-body simulations that long-lived secondary bars can form spontaneously without requiring gas, contrary to previous claims. We find that secondary bars rotate faster than primary ones. The rotation is not rigid: the secondary bars pulsate, with their amplitude and pattern speed oscillating as they rotate through the primary bars. This self-consistent study supports previous work based on orbital analysis in the potential of two rigidly rotating bars. We also characterize the density and kinematics of the N-body simulations of the double-barred galaxies, compare with observations to achieve a better understanding of such galaxies. The pulsating nature of secondary bars may have important implications for understanding the central region of double-barred galaxies.
Direct detection experiments have reached the sensitivity required to detect dark matter WIMPs. Demonstrating that a putative signal is due to WIMPs, and not backgrounds, is a major challenge however. The direction dependence of the WIMP scattering rate provides a potential WIMP `smoking gun'. If the WIMP distribution is predominantly smooth, the Galactic recoil distribution is peaked in the direction opposite to the direction of Solar motion. Previous studies have found that, for an ideal detector, of order 10 WIMP events would be sufficient to reject isotropy, and rule out an isotropic background. We examine how the median recoil direction could be used to confirm the WIMP origin of an anisotropic recoil signal. Specifically we determine the number of events required to reject the null hypothesis that the median direction is random (corresponding to an isotropic Galactic recoil distribution) at 95% confidence. We find that for zero background 31 events are required, a factor of roughly 2 more than are required to simply reject isotropy. We also investigate the effect of a non-zero isotropic background. As the background rate is increased the number of events required increases, initially fairly gradually and then more rapidly, once the signal becomes subdominant. We also discuss the effect of features in the speed distribution at large speeds, as found in recent high resolution simulations, on the median recoil direction.
Possible experimental tests are considered of recent hypotheses suggesting that TeV photons survive the pair production interaction with extragalactic background light over cosmological distances by converting to axion-like particles (ALPs) in galactic magnetic fields. The conclusion is that the CAST or CAST-like experiment may have the only chance of making a direct observation of ALPs from the sun even in the most optimistic coupling scenarios suggested by recent astrophysical data.
In the context of modified Newtonian dynamics, the fundamental plane, as the observational signature of the Newtonian virial theorem, is defined by high surface brightness objects that deviate from being purely isothermal: the line-of-sight velocity dispersion should slowly decline with radius as observed in luminous elliptical galaxies. All high surface brightness objects (e.g. globular clusters, ultra-compact dwarfs) will lie, more or less, on the fundamental plane defined by elliptical galaxies, but low surface brightness objects (dwarf spheroidals) would be expected to deviate from this relation. This is borne out by observations. With MOND, the Faber-Jackson relation (the power-law relation between luminosity and velocity dispersion), ranging from globular clusters to clusters of galaxies and including both high and low surface brightness objects, is the more fundamental and universal scaling relation in spite of its larger scatter. Faber-Jackson reflects the presence of an additional dimensional constant (the MOND acceleration) in the structure equation.
In massive primordial galaxies, the gas may directly collapse and form a single central massive object if cooling is suppressed. Line cooling by molecular hydrogen can be suppressed in the presence of a strong soft-ultraviolet radiation field, but the role played by other cooling mechanisms is less clear. In optically thin gas, Lyman-Alpha cooling can be very effective, maintaining the gas temperature below 10^4 K over many orders of magnitude in density. However, the large neutral hydrogen column densities present in primordial galaxies render them highly optically thick to Lyman-Alpha photons. In this letter, we examine in detail the effects of the trapping of these Lyman-Alpha photons on the thermal and chemical evolution of the gas. We show that despite the high optical depth in the Lyman series lines, cooling is not strongly suppressed, and proceeds via other atomic hydrogen transitions, in particular the 2s-1s and the 3-2 transitions. At densities larger than 10^9 cm^{-3}, collisional dissociation of molecular hydrogen becomes the dominant cooling process and decreases the gas temperature to about 5000 K. The gas temperature evolves with density as $T \propto \rho^{\gamma_{\rm eff} - 1}$, with $\gamma_{\rm eff} = 0.97-0.98$. The evolution is thus very close to isothermal, and so fragmentation is possible, but unlikely to occur during the initial collapse. However, after the formation of a massive central object, we expect that later-infalling, higher angular momentum material will form an accretion disk that may be unstable to fragmentation, which may give rise to star formation with a top-heavy IMF.
We use two simulations performed within the Constrained Local UniversE Simulation (CLUES) project to study both the shape and radial alignment of (the dark matter component of) subhaloes; one of the simulations is a dark matter only model while the other run includes all the relevant gas physics and star formation recipes. We find that the involvement of gas physics does not have a statistically significant effect on either property -- at least not for the most massive subhaloes considered in this study. However, we observe in both simulations including and excluding gasdynamics a (pronounced) evolution of the dark matter shapes of subhaloes as well as of the radial alignment signal since infall time. Further, this evolution is different when positioned in the central and outer regions of the host halo today; while subhaloes tend to become more aspherical in the central 50% of their host's virial radius, the radial alignment weakens in the central regime while strengthening in the outer parts. We confirm that this is due to tidal torquing and the fact that subhaloes at pericentre move too fast for the alignment signal to respond.
In this paper we derive ages and masses for 276 clusters in the merger galaxy NGC 3256. This was achieved by taking accurate photometry in four wavebands from archival HST images. Photometric measurements are compared to synthetic stellar population (SSP) models to find the most probable age, mass and extinction. The cluster population of NGC 3256 reveals an increase in the star formation rate over the last 100 million years and the initial cluster mass function (ICMF) is best described by a power law relation with slope $\alpha = 1.85 \pm 0.12$. Using the observed cluster population for NGC 3256 we calculate the implied mass of clusters younger than 10 million years old, and convert this to a cluster formation rate over the last 10 million years. Comparison of this value with the star formation rate (SFR) indicates the fraction of stars found within bound clusters after the embedded phase of cluster formation, $\Gamma$, is $22.9% \pm^{7.3}_{9.8} $ for NGC 3256. We carried out an in-depth analysis into the errors associated with such calculations showing that errors introduced by the SSP fitting must be taken into account and an unconstrained metallicity adds to these uncertainties. Observational biases should also be considered. Using published cluster population data sets we calculate $\Gamma$ for six other galaxies and examine how $\Gamma$ varies with environment. We show that $\Gamma$ increases with the star formation rate density and can be described as a power law type relation of the form $\Gamma(%) = (29.0\pm{6.0}) \Sigma_{SFR}^{0.24\pm0.04} (\msol yr^{-1} kpc^{-2})$.
In this paper we analyze the possibility of detecting nontrivial quantum phenomena in observations of the temperature anisotropy of the cosmic background radiation (CBR), for example, if the Universe could be found in a coherent superposition of two states corresponding to different CBR temperature self-correlations. Such observations are sensitive to scalar primordial fluctuations but insensitive to tensor fluctuations, which are therefore converted into an environment for the former. Even for a free inflaton field minimally coupled to gravity, scalar-tensor interactions induce enough decoherence among histories of the scalar fluctuations as to render them classical under any realistic probe of their amplitudes.
The Arecibo L-band Feed Array (ALFA) is being used to conduct a low-Galactic latitude survey, to map the distribution of galaxies and large-scale structures behind the Milky Way through detection of galaxies' neutral hydrogen (HI) 21-cm emission. This Zone of Avoidance (ZOA) survey finds new HI galaxies which lie hidden behind the Milky Way, and also provides redshifts for partially-obscured galaxies known at other wavelengths. Before the commencement of the full survey, two low-latitude precursor regions were observed, totalling 138 square degrees, with 72 HI galaxies detected. Detections through the inner Galaxy generally have no cataloged counterparts in any other waveband, due to the heavy extinction and stellar confusion. Detections through the outer Galaxy are more likely to have 2MASS counterparts. We present the results of these precursor observations, including a catalog of the detected galaxies, with their HI parameters. The survey sensitivity is well described by a flux- and linewidth-dependent signal-to-noise ratio of 6.5. ALFA ZOA galaxies which also have HI measurements in the literature show good agreement between our measurements and previous work. The inner Galaxy precursor region was chosen to overlap the HI Parkes Zone of Avoidance Survey so ALFA performance could be quickly assessed. The outer Galaxy precursor region lies north of the Parkes sky. Low-latitude large-scale structure in this region is revealed, including an overdensity of galaxies near l = 183 deg and between 5000 - 6000 km/s in the ZOA. The full ALFA ZOA survey will be conducted in two phases: a shallow survey using the observing techniques of the precursor observations, and also a deep phase with much longer integration time, with thousands of galaxies predicted for the final catalog.
The possibility of creation of cosmologically significant antimatter are analyzed in different scenarios of baryogenesis. It is argued that there may exist plenty of antimatter even in our Galaxy. Possible forms of antimatter objects and their observational signatures are discussed.
We develop a new covariant formalism to treat spherically symmetric spacetimes in metric} f(R) theories of gravity. Using this formalism we derive the general equations for a static and spherically symmetric metric in a general f(R)-gravity. These equations are used to determine the conditions for which the Schwarzschild metric is the only vacuum solution with vanishing Ricci scalar. We also show that our general framework provides a clear way of showing that the Schwarzschild solution is not a unique static spherically symmetric solution, providing some incite on how the current form of Birkhoff's theorem breaks down for these theories.
We present a framework for studying gravitational lensing in spherically symmetric spacetimes using 1+1+2 covariant methods. A general formula for the deflection angle is derived and we show how this can be used to recover the standard result for the Schwarzschild spacetime.
We present a framework for the study of lensing in spherically symmetric spacetimes within the context of f(R) gravity. Equations for the propagation of null geodesics, together with an expression for the bending angle are derived for any f(R) theory and then applied to an exact spherically symmetric solution of R^n gravity. We find that for this case more bending is expected for R^n gravity theories in comparison to GR and is dependent on the value of n and the value of distance of closest approach of the incident null geodesic.
Gravitational wave observations will be excellent tools for making precise measurements of processes that occur in very strong-field regions of spacetime. Extreme mass ratio systems, formed by the capture of a stellar mass body compact by a massive black hole, will be targets for planned space-based interferometers such as LISA and DECIGO. These systems will be especially powerful tools for testing the spacetime nature of black hole candidates. In this writeup of the talk I gave at JGRG19, I describe how the properties of black holes are imprinted on their waveforms, and how measurements can be used to study these properties and thereby learn about the astrophysics of black holes and about strong-field gravity.
The optimal reconstruction of cosmic metric perturbations and other signals requires knowledge of their power spectra and other parameters. If these are not known a priori, they have to be measured simultaneously from the same data used for the signal reconstruction. We formulate the general problem of signal inference in the presence of unknown parameters within the framework of information field theory. We develop a generic parameter uncertainty renormalized estimation (PURE) technique and address the problem of reconstructing Gaussian signals with unknown power-spectrum with five different approaches: (i) separate maximum-a-posteriori (MAP) power spectrum measurement and subsequent reconstruction, (ii) MAP reconstruction with marginalized power-spectrum, (iii) maximizing the joint posterior of signal and spectrum, (iv) guessing the spectrum from the variance in the Wiener filter map, and (v) renormalization flow analysis of the field theoretical problem providing the PURE filter. In all cases, the reconstruction can be described or approximated as Wiener filter operations with assumed signal spectra derived from the data according to the same recipe, but with differing coefficients. All of these filters, except the renormalized one, exhibit a perception threshold in case of a Jeffreys prior for the unknown spectrum. Data modes, with variance below this threshold do not affect the signal reconstruction at all. Filter (iv) seems to be similar to the so called Karhune-Loeve and Feldman-Kaiser-Peacock estimators for galaxy power spectra used in cosmology, which therefore should also exhibit a marginal perception threshold if correctly implemented. We present statistical performance tests and show that the PURE filter is superior to the others.
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Dome A, the highest plateau in Antarctica, is being developed as a site for an astronomical observatory. The planned telescopes and instrumentation and the unique site characteristics are conducive toward Type Ia supernova surveys for cosmology. A self-contained search and survey over five years can yield a spectro-photometric time series of ~1000 z<0.08 supernovae. These can serve to anchor the Hubble diagram and quantify the relationship between luminosities and heterogeneities within the Type Ia supernova class, reducing systematics. Larger aperture (>4-m) telescopes are capable of discovering supernovae shortly after explosion out to z~3. These can be fed to space telescopes, and can isolate systematics and extend the redshift range over which we measure the expansion history of the universe.
We derive the slow-roll conditions for a non-minimally coupled scalar field (extended quintessence) during the radiation/matter dominated era extending our previous results for thawing quintessence. We find that the ratio $\ddot\phi/3H\dot\phi$ becomes constant but negative, in sharp contrast to the ratio for the minimally coupled scalar field. We also find that the functional form of the equation of state of the scalar field asymptotically approaches that of the minimally coupled thawing quintessence.
The LCDM cosmological model assumes the existence of a small cosmological constant in order to explain the observed accelerating cosmic expansion. Despite the dramatic improvement of the quality of cosmological data during the last decade it remains the simplest model that fits remarkably well (almost) all cosmological observations. In this talk I review the increasingly successful fits provided by LCDM on recent geometric probe data of the cosmic expansion. I also briefly discuss some emerging shortcomings of the model in attempting to fit specific classes of data (eg cosmic velocity dipole flows and cluster halo profiles). Finally, I summarize recent results on the theoretically predicted matter overdensity ($\delta_m=\frac{\delta \rho_m}{\rho_m}$) evolution (a dynamical probe of the cosmic expansion), emphasizing its scale and gauge dependence on large cosmological scales in the context of general relativity. A new scale dependent parametrization which describes accurately the growth rate of perturbations even on scales larger than 100h^{-1}Mpc is shown to be a straightforward generalization of the well known scale independent parametrization f(a)=\omms(a)^\gamma valid on smaller cosmological scales.
After cosmic inflation and before the transition to radiation domination, the cosmic energy density may have been dominated during an extended period by an oscillating massive scalar condensate. We show that during this period, sub-Hubble scale perturbations are subject to a metric preheating instability in the narrow resonance regime. We analyze in detail both, quadratic and quartic potentials. The instability leads to the growth of density perturbations which in many cases become non-linear already before the beginning of a radiation dominated Universe. This is particularly the case when requiring a phenomenologically preferred low reheat temperature. These early structures may lead to the emission of gravitational waves and the production of primordial black holes. Furthermore, it is not clear if they could modify the prediction of linear curvature perturbations on very large scales.
In this brief, partial, incomplete and egregiously self-citing review I will summarise some of the key results in the past few years in surveys for dusty star-forming galaxies and some exciting prospects for forthcoming surveys.
The supernova (SN) delay-time distribution (DTD) - the SN rate versus time that would follow a brief burst of star formation - can shed light on SN progenitors, and on chemical enrichment timescales. Previous attempts to recover the DTD have used comparisons of mean SN rates vs. redshift to cosmic star-formation history (SFH), or comparison of SN rates among galaxies of different mean ages. We present an approach to recover the SN DTD that avoids such averaging. We compare the SFHs of individual galaxies to the numbers of SNe discovered in each galaxy (generally zero, sometimes one or a few SNe). We apply the method to a subsample of 3505 galaxies, hosting 82 SNe Ia and 119 core-collapse SNe (CC SNe), from the Lick Observatory SN Search (LOSS), with SFHs reconstructed from SDSS spectra. We find a >2sigma SN Ia DTD signal in our shortest-delay, "prompt", bin at <420 Myr. Despite a systematic error, due to the limited aperture of the SDSS spectroscopic fibres, which causes some of the prompt signal to leak to the later DTD bins, the data require a prompt SNe Ia at the 99% confidence. We further find, at 4sigma, SNe Ia that are "delayed" by > 2.4 Gyr. Thus, the data support the existence of both prompt and delayed SNe Ia. The time integral over the CC SN DTD is 0.010+/-0.002 SNe per Msun, as expected if all stars of mass >8 Msun lead to visible SN explosions. This argues against a minimum mass for CC SNe of >10 Msun, and against a significant fraction of massive stars that collapse without exploding. For SNe Ia, the time-integrated DTD is 0.0023+/-0.0006 SNe per Msun formed, most of them with delays < 2.4 Gyr. We show, using simulations, that application of the method to the full existing LOSS sample, but with complete and unbiased SFH estimates for the survey galaxies, could provide a detailed measurement of the SN Ia DTD.
Studying outliers from the bimodal distribution of galaxies in the color-mass space, such as morphological early-type galaxies residing in the blue cloud, can help to better understand the physical mechanisms that lead galaxy migrations in this space. In this paper we study the evolution of the properties of 210 M*/Msol>10^10 blue E/S0s between z~1.4 and z~0.2 in the COSMOS field with confirmed spectroscopic redshifts from the zCOSMOS 10k release. We first observe that the threshold mass, defined at z=0 in previous studies as the mass below which the population of blue early-type galaxies starts to be abundant relative to passive E/S0s, evolves from log(M*/Msol)~10.1 at z~0.3 to log(M*/Msol)~10.9 at z~1. Second, there seems to be a turn-over mass in the nature of blue E/S0 galaxies. Above log(M*/Msol)~10.8 blue E/S0 resemble to merger remnants probably migrating to the red-sequence in a time-scale of ~3 Gyr. Below this mass, they seem to be closer to normal late-type galaxies as if they were the result of minor mergers which triggered the central star-formation and built a central bulge component or were (re)building a disk from the surrounding gas, suggesting that they are moving back or staying in the blue-cloud. This turn-over mass does not seem to evolve significantly from z~1 in contrast with the threshold mass and therefore does not seem to be linked with the relative abundance of blue E/S0s.
This is the fourth paper in a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. We observed for this purpose the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. We have analysed the HI channel maps to accurately measure all four functions that describe the HI kinematics and 3D distribution: the radial HI surface density, the HI vertical thickness, the rotation curve and the HI velocity dispersion. In this paper we analyse these data for the edge-on galaxy UGC7321. We measured the stellar mass distribution ($M=3\times10^8$ \msun with $M/L_R\lesim0.2$), finding that the vertical force of the gas disk dominates the stellar disk at all radii. We find that the vertical force puts a much stronger constraint on the stellar mass-to-light ratio than rotation curve decomposition. Fitting of the vertical force field derived from the flaring and velocity dispersion of the HI revealed that UGC7321 has a spherical halo density distribution with a flattening of $q = c/a = 1.0 \pm 0.1$.
The observed super-massive black hole (SMBH) mass -- galaxy velocity
dispersion ($M_{\rm cmo} - \sigma$) correlation, and the similar correlation
for nuclear star clusters, may be established when winds/outflows from the CMO
("central massive object") drive gas out of the potential wells of classical
bulges. Timescales of growth for these objects may explain why smaller bulges
appear to host preferentially NCs while larger ones contain SMBHs only.
Despite much recent progress, feedback processes in bulge/galaxy formation
are far from being understood. Our numerical simulations show that that
understanding how the CMO feeds is as important a piece of the puzzle as
understanding how its feedback affects its host galaxy.
We review models which generate a large non-Gaussianity of the local form. We first briefly consider three models which generate the non-Gaussianity either at or after the end of inflation; the curvaton scenario, modulated (p)reheating and an inhomogeneous end of inflation. We then focus on ways of generating the non-Gaussianity during inflation. We derive general conditions which a product or sum separable potential must satisfy in order to generate a large local bispectrum during slow-roll inflation. As an application we consider two-field hybrid inflation. We then derive a formalism not based on slow roll which can be applied to models in which the slow-roll parameters become large before inflation ends. An exactly soluble two-field model is given in which this happens. Finally we also consider further non-Gaussian observables; a scale dependence of f_NL and the trispectrum.
Microlensing perturbations to the magnification of gravitationally lensed quasar images are dependent on the angular size of the quasar. If quasar variability at visible wavelengths is caused by a change in the area of the accretion disk, it will affect the microlensing magnification. We derive the expected signal, assuming that the luminosity scales with some power of the disk area, and estimate its amplitude using simulations. We discuss the prospects for detecting the effect in real-world data and for using it to estimate the logarithmic slope of the luminosity's dependence on disk area. Such an estimate would provide a direct test of the standard thin accretion disk model. We tried fitting 6 seasons of the light curves of the lensed quasar HE 0435-1223 including this effect as a modification to the Kochanek et al. (2006) approach to estimating time delays. We find a dramatic improvement in the goodness of fit and relatively plausible parameters, but a robust estimate will require a full numerical calculation in order to correctly model the strong correlations between the structure of the microlensing magnification patterns and the magnitude of the effect. We also comment briefly on the effect of this phenomenon on the stability of time delay estimates.
A simple model for the dynamics of the Magellanic Stream (MS), in the framework of modified gravity models is investigated. We assume that the galaxy is made up of baryonic matter out of context of dark matter scenario. The model we used here is named Modified Gravity (MOG) proposed by Moffat (2005). In order to examine the compatibility of the overall properties of the MS under the MOG theory, the observational radial velocity profile of the MS is compared with the numerical results using the $\chi^2$ fit method. In order to obtain the best model parameters, a maximum likelihood analysis is performed. We also compare the results of this model with the Cold Dark Matter (CDM) halo model and the other alternative gravity model that proposed by Bekenstein (2004), so called TeVeS. We show that by selecting the appropriate values for the free parameters, the MOG theory seems to be plausible to explain the dynamics of the MS as well as the CDM and the TeVeS models.
From various cosmological, astrophysical and terrestrial requirements, we derive conservative upper bounds on the present-day fraction of the mass of the Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark matter particles are neutral but decay lately into CHAMPs, the lack of detection of heavy hydrogen in sea water and the vertical pressure equilibrium in the Galactic disc turn out to put the most stringent bounds. Adopting very conservative assumptions about the recoiling velocity of CHAMPs in the decay and on the decay energy deposited in baryonic gas, we find that the lifetime for decaying neutral DM must be > (0.9-3.4)x 10^3 Gyr. Even assuming the gyroradii of CHAMPs in the Galactic magnetic field are too small for halo CHAMPs to reach Earth, the present-day fraction of the mass of the Galactic halo in CHAMPs should be < (0.4-1.4)x 10^{-2}. We show that redistributing the DM through the coupling between CHAMPs and the ubiquitous magnetic fields cannot be a solution to the cuspy halo problem in dwarf galaxies.
The WW scattering into gravitino and gaugino is here investigated in the broken phase, by using both gauge and mass eigenstates. Differently from what is obtained for unbroken gauge symmetry, we find in the scattering amplitudes new structures, which can lead to violation of unitarity above a certain scale. This happens because, in the annihilation diagram, the longitudinal degrees of freedom in the propagator of the gauge bosons disappear from the amplitude, by virtue of the SUGRA vertex. We show that the longitudinal polarizations of the on-shell W become strongly interacting in the high energy limit, and that the inclusion of diagrams with off-shell scalars of the MSSM does not cancel the divergences.
We construct an anisotropic Weyl invariant theory in the ADM formalism and discuss its cosmological consequences. It extends the original anisotropic Weyl invariance of Ho\v{r}ava-Lifshitz gravity using an extra scalar field. The action is invariant under the anisotropic transformations of the space and time metric components with an arbitrary value of the critical exponent $z$. One of the interesting features is that the cosmological constant term maintains the anisotropic symmetry for $z=-3$. We also include the ordinary matter and show that it can preserve the anisotropic Weylinvariance if the equation of state satisfies $P_m= z\rho_m/3$. Then, we study cosmology of the Einstein-Hilbert-anisotropic Weyl (EHaW) action including the ordinary matter both with or without anisotropic Weyl invariance. The correlation of the critical exponent $z$ and the equation of state parameter $\omega_m$ provides a new perspective of the cosmology. It is also shown that for particular value of $z=-3$, the EHaW action admits a late time accelerating universe.
Gravitino production in the primordial Universe is investigated into details. After briefly reviewing inflation, supersymmetry and supergravity, we first study the scattering of massive W bosons in the thermal bath of particles, during the period of reheating. It is found that the process generates in the cross section terms which eventually lead to unitarity breaking above a certain scale. This happens by virtue of the supergravity vertex. We show that the longitudinal polarizations of the on-shell W become strongly interacting in the high energy limit, and that the inclusion of diagrams with off-shell scalars of the MSSM does not cancel the divergences. Next, we consider the dynamics and the decay into gravitinos of a scalar field S, which starts oscillating in its potential at the end of inflation. We embed S in a model of gauge mediation with metastable vacua, where the hidden sector is of the O'Raifeartaigh type. By demanding that the gravitinos thus produced provide with the observed Cold Dark Matter density, we modify previous results in the literature, and find that it is easy to account for gravitino Dark Matter with an arbitrarily low reheating temperature.
The NIR Ca II triplet absorption lines have proven to be an important tool for quantitative spectroscopy of individual red giant branch stars in the Local Group, providing a better understanding of metallicities of stars in the Milky Way and dwarf galaxies and thereby an opportunity to constrain their chemical evolution processes. An interesting puzzle in this field is the significant lack of extremely metal-poor stars, below [Fe/H]=-3, found in classical dwarf galaxies around the Milky Way using this technique. The question arises whether these stars are really absent, or if the empirical Ca II triplet method used to study these systems is biased in the low-metallicity regime. Here we present results of synthetic spectral analysis of the Ca II triplet, that is focused on a better understanding of spectroscopic measurements of low-metallicity giant stars. Our results start to deviate strongly from the widely-used and linear empirical calibrations at [Fe/H]<-2. We provide a new calibration for Ca II triplet studies which is valid for -0.5<[Fe/H]<-4. We subsequently apply this new calibration to current data sets and suggest that the classical dwarf galaxies are not so devoid of extremely low-metallicity stars as was previously thought.
We study the formation of molecular precursors to dust in the ejecta of Population III supernovae using a chemical kinetic approach. Our work focuses on zero-metallicity 20 Msun and 170 Msun progenitors, and we consider fully-macroscopically mixed and unmixed ejecta. The nucleation stage for small silica, metal oxides and sulphides, pure metal, and carbon clusters is described with a new chemical reaction network. We consider the effect of the pressure dependence of critical nucleation rates, and test the impact of microscopically-mixed He+ on carbon dust formation. The unmixed ejecta of a 170 Msun progenitor supernova synthesizes ~ 5.6 Msun of small clusters, while its 20 Msun counterpart produces ~ 0.103 Msun. Our results point to smaller amounts of dust formed in the ejecta of Pop. III supernovae by a factor ~ 5 compared to values derived by previous studies, and to different dust chemical composition. Such deviations result from some erroneous assumptions made, the inappropriate use of classical nucleation theory to model dust formation, and the omission of the synthethis of molecules in supernova ejecta. Unmixed ejecta of massive Pop. III supernovae chiefly form silica and/or silicates, and pure silicon grains whereas their lower mass counterparts form a dust mixture dominated by silica and/or silicates, pure silicon and iron sulphides. Amorphous carbon can only condense in ejecta where the carbon-rich zone is deprived of He+. The first dust enrichment to the primordial gas in the early universe from Pop. III massive supernova comprises primarily pure silicon, silica and silicates. If carbon dust is present at redshift z> 6, alternative dust sources must be considered.
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[Abridged] We present reliable multiwavelength identifications and high-quality photometric redshifts for the 462 X-ray sources in the ~2 Ms Chandra Deep Field-South. Source identifications are carried out using deep optical-to-radio multiwavelength catalogs, and are then combined to create lists of primary and secondary counterparts for the X-ray sources. We identified reliable counterparts for 446 (96.5%) of the X-ray sources, with an expected false-match probability of ~6.2%. A likelihood-ratio method is used for source matching, which effectively reduces the false-match probability at faint magnitudes compared to a simple error-circle matching method. We construct a master photometric catalog for the identified X-ray sources including up to 42 bands of UV-to-infrared data, and then calculate their photometric redshifts (photo-z's). The reliability of the photo-z's is evaluated using the subsample of 220 sources with secure spectroscopic redshifts. We achieve an accuracy of ~1% [|Delta z|/(1+z)] and an outlier fraction of ~1.4% for sources with spectroscopic redshifts. We performed blind tests to derive a more realistic estimate of the photo-z quality for sources without spectroscopic redshifts. We expect there are ~9% outliers for the relatively brighter sources (R<26), and the outlier fraction will increase to ~15-25% for the fainter sources (R>26). The typical photo-z accuracy is ~6-7%. The outlier fraction and photo-z accuracy do not appear to have a redshift dependence (for z~0-4). These photo-z's appear to be the best obtained so far for faint X-ray sources, and they have been significantly (>50%) improved compared to previous estimates of the photo-z's for the X-ray sources in the ~2 Ms Chandra Deep Field-North and ~1 Ms Chandra Deep Field-South.
The mass of super massive black holes at the centre of galaxies is tightly correlated with the mass of the galaxy bulges which host them. This observed correlation implies a mechanism of joint growth, but the precise physical processes responsible are a matter of some debate. Here we report on the growth of black holes in 400 local galactic bulges which have experienced a strong burst of star formation in the past 600Myr. The black holes in our sample have typical masses of 10^6.5-10^7.5 solar masses, and the active nuclei have bolometric luminosities of order 10^42-10^44erg/s. We combine stellar continuum indices with H-alpha luminosities to measure a decay timescale of ~300Myr for the decline in star formation after a starburst. During the first 600Myr after a starburst, the black holes in our sample increase their mass by on-average 5% and the total mass of stars formed is about 1000 times the total mass accreted onto the black hole. This ratio is similar to the ratio of stellar to black hole mass observed in present-day bulges. We find that the average rate of accretion of matter onto the black hole rises steeply roughly 250Myr after the onset of the starburst. We show that our results are consistent with a simple model in which 0.5% of the mass lost by intermediate mass stars in the bulge is accreted by the black hole, but with a suppression in the efficiency of black hole growth at early times plausibly caused by supernova feedback, which is stronger at earlier times. We suggest this picture may be more generally applicable to black hole growth, and could help explain the strong correlation between bulge and black hole mass.
We report the discovery of a galaxy cluster at z=1.62 located in the Spitzer Wide-Area Infrared Extragalactic survey XMM-LSS field. This structure was selected solely as an overdensity of galaxies with red Spitzer/IRAC colors, satisfying [3.6] - [4.5] > -0.1 AB mag. Photometric redshifts derived from Subaru XMM Deep Survey (BViz-bands), UKIRT Infrared Deep Survey-Ultra-Deep Survey (UKIDSS-UDS, JK-bands), and from the Spitzer Public UDS survey (3.6-8.0 micron) show that this cluster corresponds to a surface density of galaxies at z ~ 1.6 that is more than 20 sigma above the mean at this redshift. We obtained optical spectroscopic observations of galaxies in the cluster region using IMACS on the Magellan telescope. We measured redshifts for seven galaxies in the range z=1.62-1.63 within 2.8 arcmin (< 1.4 Mpc) of the astrometric center of the cluster. The color-magnitude diagram of the galaxies in this cluster shows a strong red-sequence, dominated by a population of red galaxies with (z - J) > 1.7 mag. The photometric redshift distributions for the red galaxies are strongly peaked at z=1.62, coincident with the spectroscopically confirmed galaxies. The rest-frame (U - B) color and scatter of galaxies on the red-sequence are consistent with a mean luminosity-weighted age of 1.2 +/- 0.1 Gyr, corresponding to a formation redshift z_f = 2.40 +/- 0.15, and implying that most of the stellar mass in this cluster formed during that period.
In this talk, we discuss how to estimate the gravitational lensing effect of a local void on the CMB polarization by using the LTB model.
We present the first and so far the only simulations to follow the fine-grained phase-space structure of galaxy haloes formed from generic LCDM initial conditions. We integrate the geodesic deviation equation in tandem with the N-body equations of motion, demonstrating that this can produce numerically converged results for the properties of fine-grained phase-space streams and their associated caustics, even in the inner regions of haloes. Our effective resolution for such structures is many orders of magnitude better than achieved by conventional techniques on even the largest simulations. We apply these methods to the six Milky Way-mass haloes of the Aquarius Project. At 8 kpc from halo centre a typical point intersects about 10^14 streams with a very broad range of individual densities; the ~10^6 most massive streams contribute about half of the local dark matter density. As a result, the velocity distribution of dark matter particles should be very smooth with the most massive fine-grained stream contributing about 0.1% of the total signal. Dark matter particles at this radius have typically passed 200 caustics since the Big Bang, with a 5 to 95% range of 50 to 500. Such caustic counts are a measure of the total amount of dynamical mixing and are very robustly determined by our technique. The peak densities on present-day caustics in the inner halo almost all lie well below the mean local dark matter density. As a result caustics provide a negligible boost (<0.1%) to the predicted local dark matter annihilation rate. The effective boost is larger in the outer halo but never exceeds about 10%. Thus fine-grained streams and their associated caustics have no effect on the detectability of dark matter, either directly in Earth-bound laboratories, or indirectly through annihilation radiation.
We have measured star formation histories (SFHs) and stellar masses of galaxies detected by the Balloon-borne Large Aperture Sub-millimetre Telescope (BLAST) over approximately 9 square degrees centred on the Chandra Deep Field South. We have applied the recently developed SFH reconstruction method of Dye et al. to optical, near-infrared and mid-infrared photometry of 92 BLAST galaxies. We find significant differences between the SFHs of low mass (<10^11 M_sol) and high mass (>10^11 M_sol) galaxies. On average, low mass galaxies exhibit a dominant late burst of star formation which creates a large fraction of their stellar mass. Conversely, high mass systems tend to have a significant amount of stellar mass that formed much earlier. We also find that the high mass SFHs evolve more strongly than the low mass SFHs. These findings are consistent with the phenomenon of downsizing observed in optically selected samples of galaxies.
We study in detail how the barred galaxy fraction varies as a function of luminosity, HI gas mass, morphology and color in the Virgo cluster in order to provide a well defined, statistically robust measurement of the bar fraction in the local universe spanning a wide range in luminosity (factor of ~100) and HI gas mass. We combine multiple public data-sets (UKIDSS near-infrared imaging, ALFALFA HI gas masses, GOLDMine photometry). After excluding highly inclined systems, we define three samples where galaxies are selected by their B-band luminosity, H-band luminosity, and HI gas mass. We visually assign bars using the high resolution H-band imaging from UKIDSS. When all morphologies are included, the barred fraction is ~17-24% while for morphologically selected discs, we find that the barred fraction in Virgo is ~29-34%: it does not depend strongly on how the sample is defined and does not show variations with luminosity or HI gas mass. The barred fraction depends most strongly on the morphological composition of the sample: when the disc populations are separated into lenticulars (S0--S0/a), early-type spirals (Sa--Sb), and late-type spirals (Sbc--Sm), we find that the early-type spirals have a higher barred fraction (~45-50%) compared to the lenticulars and late-type spirals (~22-36%). This difference may be due to the higher baryon fraction of early-type discs which makes them more susceptible to bar instabilities. We do not find any evidence of barred galaxies being preferentially blue.
Motivated by suggestions of 'cosmic downsizing', in which the dominant contribution to the cosmic star formation rate density (SFRD) proceeds from higher to lower mass galaxies with increasing cosmic time, we describe the design and implementation of the Redshift One LDSS3 Emission line Survey (ROLES). ROLES is a K-selected (22.5 < K_AB < 24.0) survey for dwarf galaxies [8.5<log(M*/Msun)< 9.5] at 0.89 < z < 1.15 drawn from two extremely deep fields (GOODS-S and MS1054-FIRES). Using the [OII]3727 emission line, we obtain redshifts and star-formation rates (SFRs) for star-forming galaxies down to a limit of ~0.3 Msun/yr. We present the [OII] luminosity function measured in ROLES and find a faint end slope of alpha_faint ~ -1.5, similar to that measured at z~0.1 in the SDSS. By combining ROLES with higher mass surveys, we measure the SFRD as a function of stellar mass using [OII] (with and without various empirical corrections), and using SED-fitting to obtain the SFR from the rest-frame UV luminosity for galaxies with spectroscopic redshifts. Our best estimate of the corrected [OII]-SFRD and UV SFRD both independently show that the SFRD evolves equally for galaxies of all masses between z~1 and z~0.1. The exact evolution in normalisation depends on the indicator used, with the [OII]-based estimate showing a change of a factor of ~2.6 and the UV-based a factor of ~6. We discuss possible reasons for the discrepancy in normalisation between the indicators, but note that the magnitude of this uncertainty is comparable to the discrepancy between indicators seen in other z~1 works. Our result that the shape of the SFRD as a function of stellar mass (and hence the mass range of galaxies dominating the SFRD) does not evolve between z~1 and z~0.1 is robust to the choice of indicator. [abridged]
We explore the use of simple star-formation rate (SFR) indicators (such as may be used in high-redshift galaxy surveys) in the local Universe using [OII], Ha, and u-band luminosities from the deeper 275 deg^2 Stripe 82 subsample of the Sloan Digital Sky Survey (SDSS) coupled with UV data from the Galaxy Evolution EXplorer satellite (GALEX). We examine the consistency of such methods using the star-formation rate density (SFRD) as a function of stellar mass in this local volume, and quantify the accuracy of corrections for dust and metallicity on the various indicators. Rest-frame u-band promises to be a particularly good SFR estimator for high redshift studies since it does not require a particularly large or sensitive extinction correction, yet yields results broadly consistent with more observationally expensive methods. We suggest that the [OII]-derived SFR, commonly used at higher redshifts (z~1), can be used to reliably estimate SFRs for ensembles of galaxies, but for high mass galaxies (log(M*/Msun)>10), a larger correction than is typically used is required to compensate for the effects of metallicity dependence and dust extinction. We provide a new empirical mass-dependent correction for the [OII]-SFR.
We review the basic hypotheses which motivate the statistical framework used to analyze the cosmic microwave background, and how that framework can be enlarged as we relax those hypotheses. In particular, we try to separate as much as possible the questions of gaussianity, homogeneity and isotropy from each other. We focus both on isotropic estimators of non-gaussianity as well as statistically anisotropic estimators of gaussianity, giving particular emphasis on their signatures and the enhanced "cosmic variances" that become increasingly important as our putative Universe becomes less symmetric. After reviewing the formalism behind some simple model-independent tests, we discuss how these tests can be applied to CMB data when searching for large scale "anomalies"
We investigate the evolution of supermassive black hole mass (M_BH) and the host spheroid mass (M_sph) in order to track the history of the M_BH-M_sph relationship. The typical mass increase of M_BH is calculated by a continuity equation and accretion history, which is estimated from the active galactic nucleus (AGN) luminosity function. The increase in M_sph is also calculated by using a continuity equation and a star formation model, which uses observational data for the formation rate and stellar mass function. We find that the black hole to spheroid mass ratio is expected to be substantially unchanged since z~1.2 for high mass objects (M_BH>10^8.5M_SUN and M_sph>10^11.3M_SUN). In the same redshift range, the spheroid mass is found to increase more rapidly than the black hole mass if M_sph>10^11M_SUN. The proposed mass-dependent model is consistent with the current available observational data in the M_BH-M_sph diagram.
We model the nonlinear growth of cosmic structure in different dark energy models, using large volume N-body simulations. We consider a range of quintessence models which feature both rapidly and slowly varying dark energy equations of state, and compare the growth of structure to that in a universe with a cosmological constant. The adoption of a quintessence model changes the expansion history of the universe, the form of the linear theory power spectrum and can alter key observables, such as the horizon scale and the distance to last scattering. The difference in structure formation can be explained to first order by the difference in growth factor at a given epoch; this scaling also accounts for the nonlinear growth at the 15% level. We find that quintessence models which feature late $(z<2)$, rapid transitions towards $w=-1$ in the equation of state, can have identical baryonic acoustic oscillation (BAO) peak positions to those in $\Lambda$CDM, despite being very different from $\Lambda$CDM both today and at high redshifts $(z \sim 1000)$. We find that a second class of models which feature non-negligible amounts of dark energy at early times cannot be distinguished from $\Lambda$CDM using measurements of the mass function or the BAO. These results highlight the need to accurately model quintessence dark energy in N-body simulations when testing cosmological probes of dynamical dark energy.
We present a toy model of galaxy growth within DM haloes via gas accretion and mergers. We begin with merger trees from a DM cosmological simulation. Three processes cause the evolution of baryons to differ from that of DM: gravitational shock heating coupled to BH feedback above a halo mass Mshock=10^12MSun, cosmic reionisation in haloes vc<vreion=40 km/s, stellar feedback in haloes with vc<vSN=120km/s. Designed to reproduce the z=0 galaxy stellar mass function, our model matches reasonably well the evolution of the cosmic stellar density. It also predicts a gap between the masses of central and satellite galaxies in agreement with recent SDSS data: in low-mass haloes the mass function is highly peaked in the narrow range of central galaxy masses, whereas high-mass haloes (massive groups and clusters) contain a much more numerous satellite population. Gas accretion is the dominant growth mechanism at mstars<mcrit=10^11MSun, while galaxies with mstars>mcrit acquire most of their final mass through mergers (mostly major and dry). Cold-mode mergers (mergers in haloes with Mhalo<Mshock) are rare. Their contribution to galaxy growth is small at all masses and peaks at mstars=10^10-11MSun. We thus predict a characteristic mass scale of the same order for ULIRGs and quasar hosts. The different accretion histories of galaxies below and above m_crit explain why cold-mode (blue star-forming) galaxies are usually spirals and hot-mode (red passive) galaxies are usually ellipticals (assuming that gas accretion forms discs and mergers form spheroids). However, the contribution of mergers to the final stellar masses of galaxies with mstars<mcrit is low even in satellites of groups and clusters. Thus, red galaxies below mcrit (dSph/dE) should have structural properties that separate them from giant ellipticals.
I review work on the influence of inhomogeneities in the matter distribution on the determination of the luminosity distance of faraway sources, and the connection to the perceived cosmological acceleration.
We study the growth of matter perturbations beyond the linear level in cosmologies in which the dark energy has a variable equation of state. The non-linear corrections result in shifts in the positions of the maximum, minima and nodes of the spectrum within the range of Baryon Acoustic Oscillations. These can be used in order to distinguish theories with different late-time variability of the equation of state.
In the pre-reheating era, following cosmic inflation and preceding radiation domination, the energy density may be dominated by an oscillating massive scalar condensate, such as is the case for quadratic chaotic inflation. We have found in a previous paper that during this period, a wide range of sub-Hubble scale perturbations are subject to a preheating instability, leading to the growth of density perturbations ultimately collapsing to form non-linear structures. We compute here the gravitational wave signal due to these structures in the linear limit and present estimates for emission in the non-linear limit due to various effects: the collapse of halos, the tidal interactions, the evaporation during the conversion of the inflaton condensate into radiation and finally the ensuing turbulent cascades. The gravitational wave signal could be rather large and potentially testable by future detectors.
The handful of low-mass, late-type galaxies that comprise Hickson Compact Group 31 is in the midst of complex, ongoing gravitational interactions, evocative of the process of hierarchical structure formation at higher redshifts. With sensitive, multicolor Hubble Space Telescope imaging, we characterize the large population of <10 Myr old star clusters that suffuse the system. From the colors and luminosities of the young star clusters, we find that the galaxies in HCG 31 follow the same universal scaling relations as actively star-forming galaxies in the local Universe despite the unusual compact group environment. Furthermore, the specific frequency of the globular cluster system is consistent with the low end of galaxies of comparable masses locally. This, combined with the large mass of neutral hydrogen and tight constraints on the amount of intragroup light, indicate that the group is undergoing its first epoch of interaction-induced star formation. In both the main galaxies and the tidal-dwarf candidate, F, stellar complexes, which are sensitive to the magnitude of disk turbulence, have both sizes and masses more characteristic of z=1-2 galaxies. After subtracting the light from compact sources, we find no evidence for an underlying old stellar population in F -- it appears to be a truly new structure. The low velocity dispersion of the system components, available reservoir of HI, and current star formation rate of ~10 solar masses per year, indicate that HCG31 is likely to both exhaust its cold gas supply and merge within ~1 Gyr. We conclude that the end product will be an isolated, X-ray-faint, low-mass elliptical.
We present sensitive phase-referenced VLBI results on the radio continuum emission from the z=1.87 luminous submillimeter galaxy (SMG) GOODS 850-3. The observations were carried out at 1.4 GHz using the High Sensitivity Array (HSA). Our sensitive tapered VLBI image of GOODS 850-3 at 0.47 x 0.34 arcsec (3.9 x 2.9 kpc) resolution shows a marginally resolved continuum structure with a peak flux density of 148 \pm 38 uJy/beam, and a total flux density of 168 \pm 73 uJy, consistent with previous VLA and MERLIN measurements. The derived intrinsic brightness temperature is > 5 \pm 2 x 10^3 K. The radio continuum position of this galaxy coincides with a bright and extended near-infrared source that nearly disappears in the deep HST optical image, indicating a dusty source of nearly 9 kpc in diameter. No continuum emission is detected at the full VLBI resolution (13.2 x 7.2 mas, 111 x 61 pc), with a 4-sigma point source upper limit of 26 uJy/beam, or an upper limit to the intrinsic brightness temperature of 4.7 x 10^5 K. The extent of the observed continuum source at 1.4 GHz and the derived brightness temperature limits are consistent with the radio emission (and thus presumably the far-infrared emission) being powered by a major starburst in GOODS 850-3, with a massive star formation rate of 2500 M_sun/yr. Moreover, the absence of any continuum emission at the full resolution of the VLBI observations indicates the lack of a compact radio AGN source in this z=1.87 SMG.
Combing the three-dimensional radiative transfer (RT) calculation and cosmological SPH simulations, we study the escape fraction of ionizing photons (f_{esc}) of high-redshift galaxies at z=3-6. Our simulations cover the halo mass range of M_{h} = 10^{9} - 10^{12} M_{sun}. We postprocess several hundred simulated galaxies with the Authentic Radiative Transfer (ART) code to study the halo mass dependence of f_{esc}. In this paper, we restrict ourselves to the transfer of stellar radiation from local stellar population in each dark matter halo. We find that the average f_{esc} steeply decreases as the halo mass increases, with a large scatter for the lower mass haloes. The low mass haloes with M_{h} ~ 10^{9} M_{sun} have large values of f_{esc} (with an average of ~ 0.4), whereas the massive haloes with M_{h} ~ 10^{11} M_{sun} show small values of f_{esc} (with an average of ~ 0.07). This is because in our simulations, the massive haloes show more clumpy structure in gas distribution, and star-forming regions are embedded inside these clumps, making it more difficult for the ionizing photons to escape. On the other hand, in low mass haloes, there are often conical regions of highly ionized gas due to the shifted location of young star clusters from the center of dark matter halo, which allows the ionizing photons to escape more easily than in the high-mass haloes. By counting the number of escaped ionizing photons, we show that the star-forming galaxies can ionize the intergalactic medium at z=3-6. The main contributor to the ionizing photons is the haloes with M_{h} < 10^{10} M_{sun} owing to their high f_{esc}. The large dispersion in f_{esc} suggests that there are various sizes of H_{II} bubbles around the haloes even with the same mass.
We investigate unresolved X-ray emission from M31 based on an extensive set
of archival XMM-Newton and Chandra data. We show that extended emission, found
previously in the bulge and thought to be associated with a large number of
faint compact sources, extends to the disk of the galaxy with similar X-ray to
K-band luminosity ratio. We also detect excess X-ray emission associated with
the 10-kpc star-forming ring. The L_X/SFR ratio in the 0.5-2 keV band ranges
from zero to ~1.8 x 10^38 (erg/s)/(M_sun/yr), excluding the regions near the
minor axis of the galaxy where it is ~1.5-2 times higher. The latter is likely
associated with warm ionized gas of the galactic wind rather than with the
star-forming ring itself.
Based on this data, we constrain the nature of Classical Nova (CN)
progenitors. We use the fact that hydrogen-rich material, required to trigger
the explosion, accumulates on the white dwarf surface via accretion. Depending
on the type of the system, the energy of accretion may be radiated at X-ray
energies, thus contributing to the unresolved X-ray emission. Based on the CN
rate in the bulge of M31 and its X-ray surface brightness, we show that no more
than ~10 per cent of CNe can be produced in magnetic cataclysmic variables, the
upper limit being ~3 per cent for parameters typical for CN progenitors. In
dwarf novae, >~90-95 per cent of the material must be accreted during
outbursts, when the emission spectrum is soft, and only a small fraction in
quiescent periods, characterized by rather hard spectra.
We aim to place upper limits on the combined X-ray emission from the population of steady nuclear-burning white dwarfs in galaxies. In the framework of the single-degenerate scenario these systems are believed to be likely progenitors of Type Ia supernovae. From the Chandra archive, we selected normal early-type galaxies with the point source detection sensitivity better than 10^37 erg/s to minimize the contribution of unresolved low-mass X-ray binaries. The galaxies, contaminated by emission from ionized ISM, were identified based on the analysis of radial surface brightness profiles and energy spectra. The sample was complemented by the bulge of M31 and the data for the solar neighborhood. To cover a broad range of ages, we also included NGC3377 and NGC3585. Our final sample includes eight gas-poor galaxies for which we determine L_X/L_K ratios in the 0.3-0.7 keV energy band. In computing the L_X we included both unresolved emission and soft resolved sources with the color temperature of kT_bb <= 200 eV. We find that the X/K luminosity ratios are in the range of (1.7-3.2) x 10^27 erg/s/L_K,sun. The data show no obvious trends with mass, age, or metallicity of the host galaxy, although a weak anti-correlation with the Galactic NH appears to exist. It is much flatter than predicted for a blackbody emission spectrum with temperature of ~50-75 eV, suggesting that sources with such soft spectra contribute significantly less than a half to the observed X/K ratios. However, the correlation of the X/K ratios with NH has a significant scatter and in the strict statistical sense cannot be adequately described by a superposition of a power law and a blackbody components with reasonable parameters, thus precluding quantitative constraints on the contribution from soft sources. (abbr.)
There is wide agreement that Type Ia supernovae (used as standard candles for cosmology) are associated with the thermonuclear explosions of white dwarf stars. The nuclear runaway that leads to the explosion could start in a white dwarf gradually accumulating matter from a companion star until it reaches the Chandrasekhar limit, or could be triggered by the merger of two white dwarfs in a compact binary system. The X-ray signatures of these two possible paths are very different. Whereas no strong electromagnetic emission is expected in the merger scenario until shortly before the supernova, the white dwarf accreting material from the normal star becomes a source of copious X-rays for ~1e7 yr before the explosion. This offers a means of determining which path dominates. Here we report that the observed X-ray flux from six nearby elliptical galaxies and galaxy bulges is a factor of ~30-50 less than predicted in the accretion scenario, based upon an estimate of the supernova rate from their K-band luminosities. We conclude that no more than ~5 per cent of Type Ia supernovae in early type galaxies can be produced by white dwarfs in accreting binary systems, unless their progenitors are much younger than the bulk of the stellar population in these galaxies, or explosions of sub-Chandrasekhar white dwarfs make a significant contribution to the supernova rate.
We investigate the dynamics of homogeneous phase space for single-field models of inflation. Inflationary trajectories are formally attractors in phase space, but since in practice not all initial conditions lead to them, some degree of fine tuning is required for successful inflation. We explore how the dynamics of non-canonical inflation, which has additional kinetic terms that are powers of the kinetic energy, can play a role in ameliorating the initial conditions fine tuning problem. We present a qualitative analysis of inflationary phase space based on the dynamical behavior of the scalar field. This allows us to construct the flow of trajectories, finding that trajectories generically decay towards the inflationary solution at a steeper angle for non-canonical kinetic terms, in comparison to canonical kinetic terms, so that a larger fraction of the initial-conditions space leads to inflation. Thus, non-canonical kinetic terms can be important for removing the initial conditions fine-tuning problem of some small-field inflation models.
We present an analysis of STIS/HST optical spectra of a sample of ten Seyfert galaxies aimed at studying the structure and physical properties of the coronal-line region (CLR). The high-spatial resolution provided by STIS allowed us to resolve the CLR and obtain key information about the kinematics of the coronal-line gas, measure directly its spatial scale, and study the mechanisms that drive the high-ionisation lines. We find CLRs extending from just a few parsecs (~10 pc) up to 230 pc in radius, consistent with the bulk of the coronal lines (CLs) originating between the BLR and NLR, and extending into the NLR in the case of [FeVII] and [NeV] lines. The CL profiles strongly vary with the distance to the nucleus. We observed line splitting in the core of some of the galaxies. Line peak shifts, both red- and blue-shifts, typically reached 500 km/s, and even higher velocities (1000 km/s) in some of the galaxies. In general, CLs follow the same pattern of rotation curves as low-ionisation lines like [OIII]. From a direct comparison between the radio and the CL emission we find that neither the strength nor the kinematics of the CLs scale in any obvious and strong way with the radio jets. Moreover, the similarity of the flux distributions and kinematics of the CLs and low-ionisation lines, the low temperatures derived for the gas, and the success of photoionisation models to reproduce, within a factor of few, the observed line ratios, point towards photoionisation as the main driving mechanism of CLs.
We have used the SINFONI integral field spectrograph to map the near-infrared K-band emission lines of molecular and ionised hydrogen in the central regions of two cool core galaxy clusters, Abell 2597 and Sersic 159-03. Gas is detected out to 20 kpc from the nuclei of the brightest cluster galaxies and found to be distributed in clumps and filaments around it. The ionised and molecular gas phases trace each other closely in extent and dynamical state. Both gas phases show signs of interaction with the active nucleus. Within the nuclear regions the kinetic luminosity of this gas is found to be somewhat smaller than the current radio luminosity. Outside the nuclear region the gas has a low velocity dispersion and shows smooth velocity gradients. There is no strong correlation between the intensity of the molecular and ionised gas emission and either the radio or X-ray emission. The molecular gas in Abell 2597 and Sersic 159-03 is well described by a gas in local thermal equilibrium (LTE) with a single excitation temperature T_exc ~ 2300 K. The emission line ratios do not vary strongly as function of position, with the exception of the nuclear regions where the ionised to molecular gas ratio is found decrease. These constant line ratios imply a single source of heating and excitation for both gas phases.
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We use the multi-epoch, mid-infrared Spitzer Deep, Wide-Field Survey to investigate the variability of 474,179 objects in 8.1 deg^2 of the NDWFS Bootes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 micron bands. We find that 1.1% of the studied sample meet our standard selection criteria for being classed as a variable source. We require that the 3.6 and 4.5 micron light-curves are strongly correlated (r>0.8) and that their joint variance exceeds that for all sources with the same magnitude by 2 sigma. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBootes survey, radio catalogs, 24 micron-selected AGN candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects. Most of the stellar, galaxy and unclassified sources are false positives. For our standard selection criteria, 11-12% of the mid-IR counterparts to X-ray sources, 24 micron-selected AGN candidates and spectroscopically identified AGNs show variability. Mid-IR AGN variability can be well described by a single power-law structure function with a power-law index of 0.5 at both 3.6 and 4.5 microns, and an amplitude of 0.1 mag on rest-frame time scales of 2 years. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities. (Abridged)
The first stars in the history of the Universe are likely to form in the dense central regions of 10^5-10^6 Msolar cold dark matter halos at z=10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that dark stars at z>6 are intrinsically too faint to be detected by JWST. However, by exploiting foreground galaxy clusters as gravitational telescopes, certain varieties of cool (Teff < 30000 K) dark stars should be within reach at redshifts up to z=10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least 1 percent of the total stellar mass in such objects.
We study the population of compact stellar clusters (CSCs) in M81, using the HST/ACS images in the filters F435W, F606W and F814W covering, for the first time, the entire optical extent of the galaxy. Our sample contains 435 clusters of FWHM less than 10 ACS pixels (9 pc). The sample shows the presence of two cluster populations, a blue group of 263 objects brighter than B=22 mag, and a red group of 172 objects, brighter than B=24 mag. Based on the analysis of colour magnitude diagrams and making use of simple stellar population models, we find the blue clusters are younger than 300 Myr with some clusters as young as few Myr, and the red clusters are as old as globular clusters. The luminosity function of the blue group follows a power-law distribution with an index of 2.0, typical value for young CSCs in other galaxies. The power-law shows unmistakable signs of truncation at I=18.0 mag (M_I=-9.8 mag), which would correspond to a mass-limit of 4x10^4 M_solar if the brightest clusters are younger than 10 Myr. The red clusters have photometric masses between 10^5 to 2x10^7 M_solar for the adopted age of 5 Gyr and their luminosity function resembles very much the globular cluster luminosity function in the Milky Way. The brightest GC in M81 has M_B^0=-10.3 mag, which is ~0.9 mag brighter than w-Cen, the most massive GC in the Milky Way.
We calculate the gravitational wave signal from the growth of 10 million
solar mass supermassive black holes (SMBH) from the remnants of Population III
stars. The assembly of these lower mass black holes is particularly important
because observing SMBHs in this mass range is one of the primary science goals
for the Laser Interferometer Space Antenna (LISA), a planned NASA/ESA mission
to detect gravitational waves. We use high resolution cosmological N-body
simulations to track the merger history of the host dark matter halos, and
model the growth of the SMBHs with a semi-analytic approach that combines
dynamical friction, gas accretion, and feedback. We find that the most common
source in the LISA band from our volume consists of mergers between
intermediate mass black holes and SMBHs at redshifts less than 2.
This type of high mass ratio merger has not been widely considered in the
gravitational wave community; detection and characterization of this signal
will likely require a different technique than is used for SMBH mergers or
extreme mass ratio inspirals. We find that the event rate of this new LISA
source depends on prescriptions for gas accretion onto the black hole as well
as an accurate model of the dynamics on a galaxy scale; our best estimate
yields about 40 sources with a signal-to-noise ratio greater than 30 occur
within a volume like the Local Group during SMBH assembly -- extrapolated over
the volume of the universe yields roughly 500 observed events over 10 years,
although the accuracy of this rate is affected by cosmic variance.
Oscillons are extremely long lived, oscillatory, spatially localized field configurations that arise from generic initial conditions in a large number of non-linear field theories. With an eye towards their cosmological implications, we investigate their properties in an expanding universe. We (1) provide an analytic solution for one dimensional oscillons (for the models under consideration) and discuss their generalization to 3 dimensions, (2) discuss their stability against long wavelength perturbations and (3) estimate the effects of expansion on their shapes and life-times. In particular, we discuss a new, extended class of oscillons with surprisingly flat tops. We show that these flat topped oscillons are more robust against collapse instabilities in (3+1) dimensions than their usual counterparts. Unlike the solutions found in the small amplitude analysis, the width of these configurations is a non-monotonic function of their amplitudes.
A goal of forthcoming imaging surveys is to use weak gravitational lensing shear measurements to constrain dark energy. We quantify the importance of uncalibrated photometric redshift outliers to the dark energy goals of forthcoming imaging surveys in a manner that does not assume any particular photometric redshift technique or template. In so doing, we provide an approximate blueprint for computing the influence of specific outlier populations on dark energy constraints. We find that outliers whose photo-z distributions are tightly localized about a significantly biased redshift must be controlled to a per-galaxy rate of <~ a few times 10^-3 to insure that systematic errors on dark energy parameters are rendered negligible. In the complementary limit, a subset of imaged galaxies with uncalibrated photometric redshifts distributed over a broad range must be limited to fewer than a per-galaxy error rate of <~ a few times 10^-4. Additionally, we explore the relative importance of calibrating the photo-z's of a core set of relatively well-understood galaxies as compared to the need to identify potential catastrophic photo-z outliers. We discuss the degradation of the statistical constraints on dark energy parameters induced by excising source galaxies at high- and low-photometric redshifts, concluding that removing galaxies with z_phot >~ 2.4 and z_phot <~ 0.3 may mitigate damaging catastrophic redshift outliers at a relatively small (~ 20%) cost in statistical error. In an appendix, we show that forecasts for the degradation in dark energy parameter constraints due to uncertain photometric redshifts depend sensitively on the treatment of the nonlinear matter power spectrum. Previous work using PD96 may have overestimated the photo-z calibration requirements of future surveys.
Approximately half the baryons in the local Universe are thought to reside in the warm-hot intergalactic medium (WHIM). Emission lines from metals in the UV band are excellent tracers of the cooler fraction of this gas. We present predictions for the surface brightness of a sample of UV lines that could potentially be observed by the next generation of UV telescopes at z<1. We use a subset of simulations from the OWLS project to create emission maps and to investigate the effect of varying the physical prescriptions for star formation, supernova and AGN feedback, chemodynamics and radiative cooling. Most models produce results in agreement within a factor of a few, indicating that the predictions are robust. Of the lines we consider, C III is the strongest line, but it typically traces gas colder than 10^5 K. The same is true for Si IV. The second strongest line, C IV, traces circum-galactic gas with T~10^5 K. O VI and Ne VIII probe the warmer (T~10^5.5 K and T~10^6 K, respectively) and more diffuse gas that may be a better tracer of the large scale structure. N V emission is intermediate between C IV and O VI. The intensity of all emission lines increases strongly with gas density and metallicity, and for the bright emission it is tightly correlated with the temperature for which the line emissivity is highest. In particular, the C III, C IV, Si IV and O VI emission that is sufficiently bright to be potentially detectable in the near future (>10^3 photon/s/cm^2/sr), comes from relatively dense (rho>10^2 rho_mean) and metal rich (Z>0.1 Z_sun) gas. As such, emission lines are highly biased tracers of the missing baryons and are not an optimal tool to close the baryon budget. However, they do provide a powerful means to detect the gas cooling onto or flowing out of galaxies and groups. (Abridged)
We discuss how the effective radius Phi(Re) function (ERF) recently worked out by Bernardi et al. (2009) represents a new testbed to improve the current understanding of Semi-analytic Models of Galaxy formation. In particular, we here show that a detailed hierarchical model of structure formation can broadly reproduce the correct peak in the size distribution of local early-type galaxies, although it significantly overpredicts the number of very compact and very large galaxies. This in turn is reflected in the predicted size-mass relation, much flatter than the observed one, due to too large (~3 kpc) low-mass galaxies (<10^11 \msun), and to a non-negligible fraction of compact (< 0.5-1 kpc) and massive galaxies (> 10^11 \msun). We also find that the latter discrepancy is smaller than previously claimed, and limited to only ultracompact (Re < 0.5 kpc) galaxies when considering elliptical-dominated samples. We explore several causes behind these effects. We conclude that the former problem might be linked to the initial conditions, given that large and low-mass galaxies are present at all epochs in the model. The survival of compact and massive galaxies might instead be linked to their very old ages and peculiar merger histories. Overall, knowledge of the galactic stellar mass {\em and} size distributions allows a better understanding of where and how to improve models.
We present an analysis of the Ly-a forest toward 3C 273 from the Space Telescope Imaging Spectrograph at ~7 km/s resolution, along with re-processed data from the Far Ultraviolet Spectroscopic Explorer. The high UV flux of 3C 273 allows us to probe the weak, low z absorbers. The main sample consists of 21 HI absorbers that we could discriminate to a sensitivity of log NHI~ 12.5. The redshift density for absorbers with 13.1<log NHI<14.0 is ~1.5 sigma below the mean for other lines of sight; for log NHI >= 12.5, it is consistent with numerical model predictions. The Doppler parameter distribution is consistent with other low z samples. We find no evidence for a break in the column density power-law distribution to log NHI=12.3. A broad Ly-a absorber (BLA) is within Delta v =< 50 km/s and 1.3 local frame Mpc of two ~0.5L* galaxies, with an OVI absorber ~700 km/s away, similarly close to three galaxies and indicating overdense environments. We detect clustering on the Delta v<1000 km/s scale at 3.4 sigma significance for log NHI >= 12.6, consistent with the level predicted from hydrodynamical simulations, and indication for a Ly-a forest void at 0.09<z<0.12. We find at least two components for the z=0.0053 Virgo absorber, but the total NHI column is not significantly changed.
Using numerical ray tracing, the paper studies how the average distance modulus in an inhomogeneous universe differs from its homogeneous counterpart. The averaging is over all directions from a fixed observer not over all possible observers (cosmic), thus it is more directly applicable to our observations. Unlike previous studies, the averaging is exact, non-perturbative, and includes all possible non-linear effects. The inhomogeneous universes are represented by Sweese-cheese models containing random and simple cubic lattices of mass-compensated voids. The Earth observer is in the homogeneous cheese which has an Einstein - de Sitter metric. For the first time, the averaging is widened to include the supernovas inside the voids by assuming the probability for supernova emission from any comoving volume is proportional to the rest mass in it. Despite the well known argument for photon flux conservation, the average distance modulus correction at low redshifts is not zero due to the peculiar velocities. A formula for the maximum possible average correction as a function of redshift is derived and shown to be in excellent agreement with the numerical results. The actual average correction calculated in random and simple cubic void lattices is severely damped below the predicted maximal average. That is traced to cancelations between the corrections coming from the fronts and backs of different voids at the same redshift from the observer. The calculated correction at low redshifts allows one to readily predict the redshift at which the averaged fluctuation in the Hubble diagram is below a required precision and suggests a method to extract the background Hubble constant from low redshift data without the need to correct for peculiar velocities.
We study Friedmann-Robertson-Walker cosmological models with matter content composed of two perfect fluids $\rho_1$ and $\rho_2$, with barotropic pressure densities $p_1/ \rho_1=\omega_1=const$ and $p_2/ \rho_2=\omega_2=const$, where one of the energy densities is given by $\rho_1=C_1 a^\alpha + C_2 a^\beta$, with $C_1$, $C_2$, $\alpha$ and $\beta$ taking constant values. We solve the field equations by using the conservation equation without breaking it into two interacting parts with the help of a coupling interacting term $Q$. Nevertheless, with the found solution may be associated an interacting term $Q$, and then a number of cosmological interacting models studied in the literature correspond to particular cases of our cosmological model. Specifically those models having constant coupling parameters $\tilde{\alpha}$, $\tilde{\beta}$ and interacting terms given by $Q=\tilde{\alpha} H \rho_{_{DM}}$, $Q=\tilde{\alpha} H \rho_{_{DE}}$, $Q=\tilde{\alpha} H (\rho_{_{DM}}+ \rho_{_{DE}})$ and $Q=\tilde{\alpha} H \rho_{_{DM}}+\tilde{\beta} H \rho_{_{DE}}$, where $\rho_{_{DM}}$ and $\rho_{_{DE}}$ are the energy densities of dark matter and dark energy respectively. The studied set of solutions contains a class of cosmological models presenting a scaling behavior at early and at late times. On the other hand the two-fluid cosmological models considered in this paper also permit a three fluid interpretation which is also discussed. In this reinterpretation, for flat Friedmann-Robertson-Walker cosmologies, the requirement of positivity of energy densities of the dark matter and dark energy components allows the state parameter of dark energy to be in the range $-1.37 \lesssim \omega_{_{DE}}<-1/3$.
We present a new analysis of the soft and medium energy X-ray spectrum of the Seyfert 1 galaxy NGC 3516 taken with the Reflection Grating Spectrometer (RGS) and European Photon Imaging Camera (EPIC) on board the XMM-Newton observatory. We examine four observations made in October 2006. We investigate whether the observed variability is due to absorption by the warm absorber and/or is intrinsic to the source emission. We analyse in detail the EPIC-pn and RGS spectra of each observation separately. The warm absorber in NGC 3516 is found to consist of three phases of ionisation, two of which have outflow velocities of more than 1000 km/s. The third phase (the least ionised one) is much slower at 100 km/s. One of the high ionisation phases, with log xi of 2.4, is found to have a partial covering fraction of about 60%. It has previously been suggested that the passage of a cloud, part of a disk wind, in front of the source (producing a change in the covering fraction) was the cause of a significant dip in the lightcurve during one of the observations. From our modelling of the EPIC-pn and RGS spectra, we find that variation in the covering fraction cannot be solely responsible for this. We show that intrinsic change in the source continuum plays a much more significant role in explaining the observed flux and spectral variability than originally thought.
Beginning with the 2002 discovery of the "Amati Relation" of GRB spectra, there has been much interest in the possibility that this and other correlations of GRB phenomenology might be used to make GRBs into standard candles. One recurring apparent difficulty with this program has been that some of the primary observational quantities to be fit as "data" -- to wit, the isotropic-equivalent prompt energy $E_{iso}$ and the collimation-corrected "total" prompt energy energy $E_{\gamma}$ -- depend for their construction on the very cosmological models that they are supposed to help constrain. This is the so-called "Circularity Problem" of standard candle GRBs. This paper is intended to point out that the "Circularity Problem" is not in fact a problem at all, except to the extent that it amounts to a self-inflicted wound. It arises essentially because of an inapt choice of data variables -- "source-frame" variables such as $E_{iso}$, which are unnecessarily encumbered by cosmological considerations. If, instead, the empirical correlations of GRB phenomenology which are formulated in source-variables are {\it mapped to the primitive observational variables} (such as fluence) and compared to the observations in that space, then all taint of "circularity" disappears. I also describe procedures for encoding high-dimensional empirical correlations (such as between $E_{iso}$, $E_{pk}$, $t_{jet}$, and $T_{45}$) in a "Gaussian Tube" model that includes both the correlation and its intrinsic scatter, and how that source-variable model may easily be mapped to the space of primitive observables, to be convolved with the measurement errors and fashioned into a likelihood.
The formation and evolution of superdense clumps (or subhalos) is studied. Such clumps of dark matter (DM) can be produced by many mechanisms, most notably by spiky features in the spectrum of inflationary perturbations and by cosmological phase transitions. Being produced very early during the radiation dominated epoch, superdense clumps evolve as isolated objects. They do not belong to hierarchical structures for a long time after production, and therefore they are not destroyed by tidal interactions during the formation of larger structures. For DM particles with masses close to the electroweak (EW) mass scale, superdense clumps evolve towards a power-law density profile $\rho(r) \propto r^{-1.8}$ with a central core. Superdense clumps cannot be composed of standard neutralinos, since their annihilations would overproduce the diffuse gamma radiation. If the clumps are constituted of superheavy DM particles and develop a sufficiently large central density, the evolution of their central part can lead to a 'gravithermal catastrophe.' In such a case, the initial density profile turns into an isothermal profile with $\rho \propto r^{-2}$ and a new, much smaller core in the center. Superdense clumps can be bserved by gamma radiation from DM annihilations and by gravitational wave detectors, while the production of primordial black holes and cascade nucleosynthesis constrain this scenario.
We show that, observationally, the projected local density distribution in high-z clusters is shifted towards higher values compared to clusters at lower redshift. To search for the origin of this evolution, we analyze a sample of haloes selected from the Millennium Simulation and populated using semi-analytic models, investigating the relation between observed projected density and physical 3D density, using densities computed from the 10 and 3 closest neighbours. Both observationally and in the simulations, we study the relation between number of cluster members and cluster mass, and number of members per unit of cluster mass. We find that the observed evolution of projected densities reflects a shift to higher values of the physical 3D density distribution. In turn, this must be related with the globally higher number of galaxies per unit of cluster volume N/V in the past. We show that the evolution of N/V is due to a combination of two effects: a) distant clusters were denser in dark matter (DM) simply because the DM density within R_{200} (~the cluster virial radius) is defined to be a fixed multiple of the critical density of the Universe, and b) the number of galaxies per unit of cluster DM mass is remarkably constant both with redshift and cluster mass if counting galaxies brighter than a passively evolving magnitude limit. Our results highlight that distant clusters were much denser environments than today's clusters, both in galaxy number and mass, and that the density conditions felt by galaxies in virialized systems do not depend on the system mass.
The oxygen and nitrogen abundance evolutions with redshift and galaxy stellar mass in emission-line SDSS galaxies are investigated. This is the first such study for nitrogen abundances, and it provides an additional constraint for the study of the chemical evolution of galaxies. We have devised a criterion to recognize and exclude from consideration AGNs and star-forming galaxies with large errors in the line flux measurements. To select star-forming galaxies with accurate line fluxes measurements, we require that, for each galaxy, the nitrogen abundances derived with various calibrations based on different emission lines agree. Using this selection criterion, subsamples of star-forming galaxies have been extracted from catalogs of the MPA/JHU group. We found that the galaxies of highest masses, those with masses > 10^11.2 M_sun, have not been enriched in both oxygen and nitrogen over the last 3 Gyr: they have formed their stars in the so distant past that these have returned their nucleosynthesis products to the interstellar medium before z=0.25. The galaxies in the mass range from 10^11.0 M_sun to 10^11.2 M_sun do not show an appreciable enrichment in oxygen, but do show some enrichment in nitrogen: they also formed their stars before z=0.25 but later in comparison to the galaxies of highest masses; these stars have not returned nitrogen to the interstellar medium before z=0.25 because they have not had enough time to evolve. This suggests that stars with lifetimes of 2-3 Gyr contribute to the nitrogen production. Finally, galaxies with masses < 10^11 M_sun show enrichment in both oxygen and nitrogen during the last 3 Gyr: they have undergone appreciable star formation and have converted up to 20% of their mass into stars over this period.
This is a review article for The Review of Particle Physics 2010 (aka the Particle Data Book). It forms a compact review of knowledge of the cosmological parameters at the beginning of 2010. Topics included are Parametrizing the Universe; Extensions to the standard model; Probes; Bringing observations together; Outlook for the future.
In a galaxy cluster, the evolution of spiral galaxies depends on their cluster environment. Ram pressure due to the rapid motion of a spiral galaxy within the hot intracluster medium removes the galaxy's interstellar medium from the outer disk. Once the gas has left the disk, star formation stops. The passive evolution of the stellar populations should be detectable in optical spectroscopy and multi-wavelength photometry. The goal of our study is to recover the stripping age of the Virgo spiral galaxy NGC 4388, i.e. the time elapsed since the halt of star formation in the outer galactic disk using a combined analysis of optical spectra and photometry. We performed VLT FORS2 long-slit spectroscopy of the inner star-forming and outer gas-free disk of NGC 4388. We developed a non-parametric inversion tool that allows us to reconstruct the star formation history of a galaxy from spectroscopy and photometry. The tool was tested on a series of mock data using Monte Carlo simulations. The results from the non-parametric inversion were refined by applying a parametric inversion method. The star formation history of the unperturbed galactic disk is flat. The non-parametric method yields a rapid decline of star formation < 200 Myr ago in the outer disk. The parametric method is not able to distinguish between an instantaneous and a long-lasting star formation truncation. The time since the star formation has dropped by a factor of two from its pre-stripping value is 190 +- 30 Myr. We are able to give a precise stripping age that is consistent with revised dynamical models.
The lack of structure greater than 10 Gpc/h in Wilkinson Microwave Anisotropy Probe (WMAP) observations of the cosmic microwave background (CMB) favours compact Friedmann-Lemaitre-Robertson-Walker (FLRW) models of the Universe. The present best candidates based on observations are the Poincare dodecahedral space S^3/I^* and the 3-torus T^3. The residual gravity effect favours the Poincare space, while a measure space argument where the density parameter is a derived parameter favours flat spaces almost surely.
Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714, report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A detailed study of the jet components' motion reveals that the standard AGN paradigm of apparent superluminal motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape.We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an apparent superluminal motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic motions of the radio knots, produced by the precession of a continuous jet within the ambient medium.
Several studies have tried to ascertain whether or not the increase in abundance of the early-type galaxies (E-S0a's) with time is mainly due to major mergers, reaching opposite conclusions. We have tested it directly through semi-analytical modelling, by studying how the massive early-type galaxies with log(M_*/Msun)>11 at z~0 (mETGs) would have evolved backwards-in-time, under the hypothesis that each major merger gives place to an early-type galaxy. The study was carried out just considering the major mergers strictly reported by observations at each redshift, and assuming that gas-rich major mergers experience transitory phases of dust-reddened, star-forming galaxies (DSFs). The model is able to reproduce the observed evolution of the galaxy LFs at z<~1, simultaneously for different rest-frame bands (B, I, and K) and for different selection criteria on color and morphology. It also provides a framework in which apparently-contradictory results on the recent evolution of the luminosity function (LF) of massive, red galaxies can be reconciled, just considering that observational samples of red galaxies can be significantly contaminated by DSFs. The model proves that it is feasible to build up ~50-60% of the present-day mETG population at z<~1 and to reproduce the observational excess by a factor of ~4-5 of late-type galaxies at 0.8<z<1 through the coordinated action of wet, mixed, and dry major mergers, fulfilling global trends that are in general agreement with mass-downsizing. The bulk of this assembly takes place during ~1 Gyr elapsed at 0.8<z<1. The model suggests that major mergers have been the main driver for the observational migration of mass from the massive-end of the blue galaxy cloud to that of the red sequence in the last ~8 Gyr.
Discovering and studying obscured AGN at z>1-3 is important not only to complete the AGN census, but also because they can pinpoint galaxies where nuclear accretion and star-formation are coeval, and mark the onset of AGN feedback. We present the latest results on the characterization of z=1-3 galaxies selected for their high mid-infrared to optical flux ratio, showing that they are massive and strongly star-forming galaxies, and that many do host highly obscured AGN. We present a pilot program to push the search of moderately obscured AGN up to z=5-6 and discuss the perspectives of this line of research.
It has been hypothesized that the cosmic microwave background (CMB) provides a temperature floor for collapsing protostars that can regulate the process of star formation and result in a top-heavy initial mass function at high metallicity and high redshift. We examine whether this hypothesis has any testable observational consequences. First we determine, using a set of hydrodynamic galaxy formation simulations, that the CMB temperature floor would have influenced the majority of stars formed at redshifts between z=3 and 6, and probably even to higher redshift. Five signatures of CMB-regulated star formation are: (1) a higher supernova rate than currently predicted at high redshift; (2) a systematic discrepancy between direct and indirect measurements of the high redshift star formation rate; (3) a lack of surviving globular clusters that formed at high metallicity and high redshift; (4) a more rapid rise in the metallicity of cosmic gas than is predicted by current simulations; and (5) an enhancement in the abundances of alpha elements such as O and Mg at metallicities -2 < [Fe/H] < -0.5. Observations are not presently able to either confirm or rule out the presence of these signatures. However, if correct, the top-heavy IMF of high-redshift high-metallicity globular clusters could provide an explanation for the observed bimodality of their metallicity distribution.
We investigate the clustering properties of ~1550 broad-line AGNs at <z>=0.25
detected in the ROSAT All-Sky Survey (RASS) through their measured
cross-correlation function (CCF) with ~46000 Luminous Red Galaxies (LRGs) in
the Sloan Digital Sky Survey. By measuring the cross-correlation of our AGN
sample with a larger tracer set of LRGs, we both minimize shot noise errors due
to the relatively small AGN sample size and avoid systematic errors due to the
spatially-varying Galactic absorption that would affect direct measurements of
the auto-correlation function (ACF) of the AGN sample.
The measured ACF correlation length for the total RASS-AGN sample
(<L_(0.1-2.4 keV)>=1.5 x 10^(44) erg/s) is r_0=4.3^{+0.4}_{-0.5} h^(-1) Mpc and
the slope \gamma=1.7^{+0.1}_{-0.1}. Splitting the sample into low and high L_X
samples at L_(0.5-10 keV)=10^(44) erg/s, we detect an X-ray
luminosity-dependence of the clustering amplitude at the ~2.5 \sigma level. The
low L_X sample has r_0=3.3^{+0.6}_{-0.8} h^(-1) Mpc (\gamma=1.7^{+0.4}_{-0.3}),
which is similar to the correlation length of blue star-forming galaxies at low
redshift. The high L_X sample has r_0=5.4^{+0.7}_{-1.0} h^(-1) Mpc
(\gamma=1.9^{+0.2}_{-0.2}), which is consistent with the clustering of red
galaxies. From the observed clustering amplitude, we infer that the typical
dark matter halo mass harboring RASS-AGN with broad optical emission lines is
log (M_DMH/[h^(-1) M_SUN]) =12.6^{+0.2}_{-0.3}, 11.8^{+0.6}_{-\infty},
13.1^{+0.2}_{-0.4} for the total, low L_X, and high L_X RASS-AGN samples,
respectively.
The products of primordial nucleosynthesis and the cosmic microwave background (CMB) photons are relics from the early evolution of the Universe whose observations probe the standard model of cosmology and provide windows on new physics beyond the standard models of cosmology and of particle physics. In the standard, hot big bang cosmology, long before any stars have formed a significant fraction (~25%) of the baryonic mass in the Universe should be in the form of helium-4 nuclei. Since current 4He observations are restricted to low redshift regions where stellar nucleosynthesis has occurred, observations of high redshift, prestellar 4He would constitute a fundamental test of the hot, big bang cosmology. At recombination, long after big bang nucleosynthesis (BBN) has ended, the temperature anisotropy spectrum imprinted on the CMB depends on the 4He abundance through its connection to the electron density and the effect of the electron density on Silk damping. Since the relic abundance of 4He is relatively insensitive to the universal density of baryons, but is sensitive to a non-standard, early Universe expansion rate, the primordial mass fraction of 4He, Yp, offers a test of the consistency of the standard models of BBN and the CMB and, provides constraints on non-standard physics. Here, the WMAP seven year data (supplemented by other CMB experiments), which lead to an indirect determination of Yp at high redshift, are compared to the BBN predictions and to the independent, direct observations of 4He in low redshift, extragalactic HII regions. At present, given the very large uncertainties in the CMB-determined primordial 4He abundance (as well as for the helium abundances inferred from H II region observations), any differences between the BBN predictions and the CMB observations are small, at a level < 1.5 sigma.
The Wightman function and the vacuum expectation values of the field squared and of the energy-momentum tensor are obtained, for a massive scalar field with an arbitrary curvature coupling parameter, in the region between two infinite parallel plates, on the background of de Sitter spacetime. The field is prepared in the Bunch-Davies vacuum state and is constrained to satisfy Robin boundary conditions on the plates. For the calculation, a mode-summation method is used, supplemented with a variant of the generalized Abel-Plana formula. This allows to explicitly extract the contributions to the expectation values which come from each single boundary, and to expand the second-plate-induced part in terms of exponentially convergent integrals. Several limiting cases of interest are then studied. Moreover, the Casimir forces acting on the plates are evaluated, and it is shown that the curvature of the background spacetime decisively influences the behavior of these forces at separations larger than the curvature scale of de Sitter spacetime. In terms of the curvature coupling parameter and the mass of the field, two very different regimes are realized, which exhibit monotonic and oscillatory behavior of the vacuum expectation values, respectively. The decay of the Casimir force at large plate separation is shown to be power-law (monotonic or oscillating), with independence of the value of the field mass.
We present a new software tool to enable astronomers to easily compare observations of emission line ratios with those determined by photoionization and shock models, ITERA, the IDL Tool for Emission-line Ratio Analysis. This tool can plot ratios of emission lines predicted by models and allows for comparison of observed line ratios against grids of these models selected from model libraries associated with the tool. We provide details of the libraries of standard photoionization and shock models available with ITERA, and, in addition, present three example emission line ratio diagrams covering a range of wavelengths to demonstrate the capabilities of ITERA. ITERA, and associated libraries, is available from \url{this http URL}
We have investigated the impact of dissipationless minor galaxy mergers on the angular momentum of the remnant. Our simulations cover a range of initial orbital characteristics and the system consists of a massive galaxy with a bulge and disk merging with a much less massive (one-tenth or one-twentieth) gasless companion which has a variety of morphologies (disk- or elliptical-like) and central baryonic mass concentrations. During the process of merging, the orbital angular momentum is redistributed into the internal angular momentum of the final system; the internal angular momentum of the primary galaxy can increase or decrease depending on the relative orientation of the orbital spin vectors (direct or retrograde), while the initially non-rotating dark matter halo always gains angular momentum. The specific angular momentum of the stellar component always decreases independent of the orbital parameters or morphology of the satellite, the decrease in the rotation velocity of the primary galaxy is accompanied by a change in the anisotropy of the orbits, and the ratio of rotation speed to velocity dispersion of the merger remnant is lower than the initial value, not only due to an increase in the dispersion but also to the slowing -down of the disk rotation. We briefly discuss several astrophysical implications of these results, suggesting that minor mergers do not cause a "random walk" process of the angular momentum of the stellar disk component of galaxies, but rather a steady decrease. Minor mergers may play a role in producing the large scatter observed in the Tully-Fisher relation for S0 galaxies, as well as in the increase of the velocity dispersion and the decrease in $v/\sigma$ at large radii as observed in S0 galaxies.
The GeV emission of Gamma Ray Bursts, first detected by EGRET in an handful of bursts, is now an established property of roughly the 10% of all bursts, thanks to the Fermi/LAT observations. GRB 090510, a short burst, is particularly interesting because the good timing allows to derive a severe limit to theories of quantum gravity. With the dozen bursts detected in the 0.1-30 GeV band so far, we start to see some common properties: (i) the duration is often longer than the duration of the softer emission detected by the Gamma Burst Monitor (GBM) onboard Fermi; (ii) the spectrum is consistent with F(v)~v^{-1} with no strong spectral evolution; (iii) for the brightest bursts, the flux detected by the LAT decays as a power law with a typical slope: t^{-1.5}; iv) the peak energy of the GBM emission exceeds 500 keV (rest frame). These properties suggest a similar process for the origin of the GeV flux. We propose that it is afterglow synchrotron emission shortly following the start of the prompt phase. The steep decay slope suggests that the fireball emits in the radiative regime, i.e. all dissipated energy is radiated away. The large peak energy of the GBM flux suggests that electron-positron pairs might play a crucial role. The rapid onset, but with some delay, of the GeV flux with respect to the GBM one suggests that the bulk Lorentz factor Gamma of these bursts is of the order of 1000. Therefore the relatively small fraction of bursts detected at high energies might correspond to the fraction of bursts having the largest Gamma. If the emission occurs in the radiative regime we can start to understand why the observed X-ray and optical afterglow energetics are much smaller than the energetics emitted during the prompt phase.
The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49 currently provides strong evidence for the existence of intermediate mass black holes. Here we present the latest multi-wavelength results on this intriguing source in X-ray, UV and radio bands. We have refined the X-ray position to sub-arcsecond accuracy. We also report the detection of UV emission that could indicate ongoing star formation in the region around HLX-1. The lack of detectable radio emission at the X-ray position strengthens the argument against a background AGN.
We derive a simple approximate model describing the early, hours to days, UV/optical supernova emission, which is produced by the expansion of the outer <~0.01 solar mass part of the shock-heated envelope, and precedes the optical emission driven by radioactive decay. Our model includes an approximate description of the time dependence of the opacity (due mainly to recombination), and of the deviation of the emitted spectrum from a black body spectrum. We show that the characteristics of the early UV/O emission constrain the radius of the progenitor star, its envelope composition, and the ratio of the ejecta energy to its mass, E/M. For He envelopes, neglecting the effect of recombination may lead to an over estimate of progenitor radius by more than an order of magnitude. We also show that the relative extinction at different wavelengths may be inferred from the light-curves at these wave-lengths, removing the uncertainty in the estimate of progenitor radius due to reddening (but not the uncertainty in E/M due to uncertainty in absolute extinction). The early UV/O observations of the type Ib SN2008D and of the type IIp SNLS-04D2dc are consistent with our model predictions. For SN2008D we find progenitor radius to be approx. 10^11 cm, and an indication that the He envelope contains a significant C/O fraction.
We have investigated the radial g-r color gradients of early-type galaxies in the Sloan Digital Sky Survey (SDSS) DR6 in the redshift range 0.00<z<0.06. The majority of massive early-type galaxies show a negative color gradient (red-cored) as generally expected for early-type galaxies. On the other hand, roughly 30 per cent of the galaxies in this sample show a positive color gradient (blue-cored). These "blue-cored" galaxies often show strong H beta absorption line strengths and/or emission line ratios that are indicative of the presence of young stellar populations. Combining the optical data with Galaxy Evolution Explorer (GALEX) UV photometry, we find that all blue-cored galaxies show UV-optical colors that can only be explained by young stellar populations. This implies that most of the residual star formation in early-type galaxies is centrally concentrated. Blue-cored galaxies are predominantly low velocity dispersion systems. A simple model shows that the observed positive color gradients (blue-cored) are visible only for a billion years after a star formation episode for the typical strength of recent star formation. The observed effective radius decreases and the mean surface brightness increases due to this centrally-concentrated star formation episode. As a result, the majority of blue-cored galaxies may lie on different regions in the Fundamental Plane from red-cored ellipticals. However, the position of the blue-cored galaxies on the Fundamental Plane cannot be solely attributed to recent star formation but require substantially lower velocity dispersion. We conclude that a low-level of residual star formation persists at the centers of most of low-mass early-type galaxies, whereas massive ones are mostly quiescent systems with metallicity-driven red cores.
Superheavy dark matter (SHDM) exchanges energy with its environment much slower than particles with masses close to the electroweak (EW) scale and has therefore different small-scale clustering properties. Using the neutralino as candidate for the SHDM, we find that free-streaming allows the formation of DM clumps of all masses down to $\sim 260 m_\chi$ in the case of bino. If small-scale clumps evolve from a non-standard, spiky spectrum of perturbations, DM clumps may form during the radiation dominated era. These clumps are not destroyed by tidal interactions and can be extremely dense. In the case of a bino, a "gravithermal catastrophe" can develop in the central part of the most dense clumps, increasing further the central density and thus the annihilation signal. In the case of a higgsino, the annihilation signal is enhanced by the Sommerfeld effect. As a result annihilations of superheavy neutralinos in dense clumps may lead to observable fluxes of annihilation products in the form of ultrahigh energy particles, for both cases, higgsinos and binos, as lightest supersymmetric particles.
We examine optical V-band light curves in luminous eclipsing black hole X-ray binaries, using a supercritical accretion/outflow model that is more realistic than the formerly used ones. In order to compute the theoretical light curve in the binary system, we do not only apply the global analytic solution of the disk, but also include the effect of the optically thick outflow. We found that the depth of eclipse of the companion star by the disk changes dramatically when including the effect of the outflow. Due to the effect of outflow, we can reproduce the optical light curve for typical binary parameters in SS433. Our model with outflow velocity v~3000 km/s can fit whole shape of the averaged V-band light curve in SS433, but we found a possible parameter range consistent with observations, such as \dot{M}~5000-10000 L_E/c^2 (with L_E being the Eddington luminosity and $c$ being the speed of light) and T_C~10000K-14000 K for the accretion rate and donor star temperature, respectively. Furthermore, we briefly discuss observational implications for ultraluminous X-ray sources.
We report on the first Fermi Large Area Telescope (LAT) measurements of the so-called "extra-galactic" diffuse gamma-ray emission (EGB). This component of the diffuse gamma-ray emission is generally considered to have an isotropic or nearly isotropic distribution on the sky with diverse contributions discussed in the literature. The derivation of the EGB is based on detailed modelling of the bright foreground diffuse Galactic gamma-ray emission (DGE), the detected LAT sources and the solar gamma-ray emission. We find the spectrum of the EGB is consistent with a power law with differential spectral index g = 2.41+/-0.05 and intensity, I(> 100 MeV) = (1.03+/-0.17) 10^-5 cm^-2 s^-1 sr^-1, where the error is systematics dominated. Our EGB spectrum is featureless, less intense, and softer than that derived from EGRET data.
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