We have used new deep observations of the Coma cluster from GALEX to identify 13 star-forming galaxies with asymmetric morphologies in the ultraviolet. Aided by optical broad-band and H-alpha imaging, we interpret the asymmetric features as being due to star formation within gas stripped from the galaxies by interaction with the cluster environment. The selected objects display a range of structures from broad fan-shaped systems of filaments and knots (`jellyfish') to narrower and smoother tails extending up to 100 kpc in length. Some of the features have been discussed previously in the literature, while others are newly identified here. As an ensemble, the candidate stripping events are located closer to the cluster centre than other star-forming galaxies; their radial distribution is similar to that of all cluster members, dominated by passive galaxies. The fraction of blue galaxies which are undergoing stripping falls from 40% in the central 500 kpc, to less than 5% beyond 1 Mpc. We find that tails pointing away from (i.e. galaxies moving towards) the cluster centre are strongly favoured (11/13 cases). From the small number of `outgoing' galaxies with stripping signatures we conclude that the stripping events occur primarily on first passage towards the cluster centre, and are short-lived compared to the cluster crossing time. Using infall trajectories from simulations, the observed fraction of blue galaxies undergoing stripping can be reproduced if the events are triggered at a threshold radius of ~1 Mpc and detectable for ~500 Myr. HST images are available for two galaxies from our sample and reveal compact blue knots coincident with UV and H-alpha emission, apparently forming stars within the stripped material. Our results confirm that stripping of gas from infalling galaxies, and associated star formation in the stripped material, is a widespread phenomenon in rich clusters.
The influence of environment on the formation and evolution of early-type galaxies is, as yet, an unresolved issue. Constraints can be placed on models of early-type galaxy formation and evolution by examining their stellar populations as a function of environment. We present a catalogue of galaxies well suited to such an investigation. The magnitude-limited (b_J<19.45) sample was drawn from four clusters (Coma, A1139, A3558, and A930 at <z>=0.04) and their surrounds. The catalogue contains luminosities, redshifts, velocity dispersions and Lick line strengths for 416 galaxies, of which 245 are classified as early-types. Luminosity-weighted ages, metallicities, and alpha-element abundance ratios have been estimated for 219 of these early-types. We also outline the steps necessary for measuring fully-calibrated Lick indices and estimating the associated stellar population parameters using up-to-date methods and stellar population models. In a subsequent paper we perform a detailed study of the stellar populations of early-type galaxies in clusters and investigate the effects of environment.
In this paper, we present results from our study investigating the evolution of the mass-metallicity and luminosity-metallicity relation over cosmological timescales. We determine the metallicities from strong-line diagnostics for 940 emission line galaxies from the Deep Extragalactic Evolutionary Probe 2 redshift survey in the redshift range of 0.75<z<0.82. We determine masses by fitting the SED inferred from photometry with stellar population synthesis models. This relatively large sample of galaxies in a small redshift range is ideal for investigating metallicity evolution in comparison with local and high-z samples. We investigate the evolution in the mass-metallicity and luminosity-metallicity relation by comparing our determination at z~0.8 with the local relation at z~0.07 determined from the Sloan Digital Sky Survey. We show that at z~0.8 galaxies with masses log(M) > 10.5 M_solar have already achieved the level of enrichment observed in the local universe. The mass-metallicity relation for z~0.8 has slightly steeper slope than the local relation and the mean difference in metallicity is ~0.05 dex. We examine the luminosity-metallicity relation and determine that the slope of the relation at z~0.8 is consistent with the local relation. The metallicity at a given luminosity in the z~0.8 is offset from the local relation by ~0.12 dex. We attribute the discrepancy between the metallicity evolution inferred from the mass-metallicity and luminosity-metallicity relation to luminosity evolution in the population of blue star-forming galaxies. We infer a B-band luminosity evolution of ~0.8 mags for the population of star-forming galaxies. We estimate gas masses from the Schmidt-Kennicutt star formation law and determine the effective yields for our sample. We observe an effective yield that decreases with increasing stellar mass and we discuss the implications of this result.
In this paper, the Dvali-Gabadadze-Porrati (DGP) brane model is confronted by current cosmic observational data sets from geometrical and dynamical perspectives. On the geometrical side, the recent released Union2 $557$ of type Ia supernovae (SN Ia), the baryon acoustic oscillation (BAO) from Sloan Digital Sky Survey and the Two Degree Galaxy Redshift Survey (transverse and radial to line-of-sight data points), the cosmic microwave background (CMB) measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations (shift parameters $R$, $l_a(z_\ast)$ and redshift at the last scatter surface $z_\ast$), ages of high redshifts galaxies, i.e. the lookback time (LT) and the high redshift Gamma Ray Bursts (GRBs) are used. On the dynamical side, data points about the growth function (GF) of matter linear perturbations are used. Using the same data sets combination, we also constrain the flat $\Lambda$CDM model as a comparison. The results show that current geometrical and dynamical observational data sets much favor flat $\Lambda$CDM model and the deviation from it is above $6\sigma$ for spatially flat DGP model.
NGC 404, at a distance of 3.4 Mpc, is the nearest S0 galaxy. This galaxy harbors a LINER; however, since the spectrum does not show a broad H{\alpha} emission, it is not certain that this LINER is a low luminosity AGN and its nature is still an open question. HST observations show the existence of stellar populations with an age of 3 x 10^8 years years in the galactic bulge and with an age of 6-15 x 10^9 years in the galactic disk. In this work, we present an analysis of the data cube of NGC 404 obtained with the IFU (Integral Field Unity) of the GMOS (Gemini Multi-Object Spectrograph) on the Gemini North telescope.
The main goal of this paper is to give an alternative interpretation of space-like and time-like extra dimensions as a primary factor for inflation in the early universe. We introduce the 5-dimensional perfect fluid and compare the energy-momentum tensor for the bulk scalar field with space-like and time-like extra dimensions. It is shown, that additional dimensions can imply to negative pressure in the slow roll regime in the early higher-dimensional world.
Contopoulos et al. recently argued that there is observational evidence for a preferred sense of the Faraday rotation-measure gradients across jets from active galactic nuclei (AGNs). Such behaviour could arise if there were a deterministic relationship between the polarity of the poloidal magnetic field that threads the outflow and the sense of rotation of the outflow's source. Based on this interpretation, Countopoulos et al. suggested that their finding supports a model for the origin of cosmic magnetic fields in a Poynting-Robertson process operating in AGN accretion discs. Here I point out that an alternative explanation of such a relationship could be that the Hall current plays a key role in the magnetohydrodynamics of the underlying disc. In this picture, the measured Faraday rotation is dominated by the contribution of a centrifugally driven wind that is launched from the weakly ionized outer region of the disc. Additional observations are, however, needed to verify the claimed behaviour.
We analyze the morphological properties of a large sample of 1503 70 micron selected galaxies in the COSMOS field spanning the redshift range 0.01<z< 3.5 with a median redshift of 0.5 and an infrared luminosity range of 10^8<L_IR<10^14L_sun with a median luminosity of 10^11.4 L_sun. In general these galaxies are massive, with a stellar mass range of 10^10-10^12 M_sun, and luminous, with -25<M_K<-20. We find a strong correlation between the fraction of major mergers and L_IR, with the fraction at the highest luminosity being up to 50%. We also find that the fraction of spirals drops dramatically with L_IR. Minor mergers likely play a role in boosting the infrared luminosity for sources with low luminosities. The precise fraction of mergers in any given L_IR bin varies by redshift due to sources at z>1 being difficult to classify and subject to the effects of band pass shifting, therefore, these numbers can only be considered lower limits. At z<1, where the morphological classifications are most robust, major mergers clearly dominate the ULIRG population (50-80%) and are important for the LIRG population (25-40%). At z>1 the fraction of major mergers is at least 30-40% for ULIRGs. Although the general morphological trends agree with what has been observed for local (U)LIRGs, the fraction of major mergers is slightly lower than seen locally. This is in part due to the difficulty of identifying merger signatures at high redshift. We argue that given the number of major gas-rich mergers observed and the relatively short timescale that they would be observable in the (U)LIRG phase that it is plausible for the observed red sequence of massive ellipticals (<10^12 M_sun) to have been formed entirely by gas-rich major mergers.
Ultracompact minihalos (UCMHs) are dense dark matter structures which can form from large density perturbations shortly after matter-radiation equality. If dark matter is in the form of Weakly Interacting Massive Particles (WIMPs), then UCMHs may be detected via their gamma-ray emission. We investigate how the {\em{Fermi}} satellite could constrain the abundance of UCMHs and place limits on the power spectrum of the primordial curvature perturbation. Detection by {\em Fermi} would put a lower limit on the UCMH halo fraction. The smallest detectable halo fraction, $f_{\rm UCMH} \gtrsim 10^{-7}$, is for $M_{\rm UCMH} \sim 10^{3} M_{\odot}$. If gamma-ray emission from UCMHs is not detected, an upper limit can be placed on the halo fraction. The bound is tightest, $f_{\rm UCMH} \lesssim 10^{-5}$, for $M_{\rm UCMH} \sim 10^{5} M_{\odot}$. The resulting upper limit on the power spectrum of the primordial curvature perturbation in the event of non-detection is in the range $\mathcal{P_R} \lesssim 10^{-6.5}- 10^{-6}$ on scales $k \sim 10^{1}-10^{6} \, {\rm Mpc}^{-1}$. This is substantially tighter than the existing constraints from primordial black hole formation on these scales, however it assumes that dark matter is in the form of WIMPs and UCMHs are not disrupted during the formation of the Milky Way halo.
We constrain the spectrum of the cosmic ultraviolet background radiation by fitting the observed abundance ratios carbon ions at $z\sim 2\hbox{--}3$ with those expected from different models of the background radiation. We use the recently calculated modulation of the background radiation between 3 and 4 Ryd due to resonant line absorption by intergalactic HeII, and determine the ratios of CIII to CIV expected at these redshifts, as functions of metallicity, gas density and temperature. Our analysis of the observed ratios shows that 'delayed reionization' models, which assume a large fraction of HeII at $z\sim3$, is not favored by data. Our results suggest that HeII reionization was inhomogeneous, consistent with the predictions from recent simulations.
We present an analysis of star formation and nuclear activity of about 28000 galaxies in a volume-limited sample taken from SDSS DR4 low-redshift catalogue (LRC) taken from the New York University Value Added Galaxy Catalogue (NYU-VAGC) of Blanton et al. 2005, with 0.005<z<0.037, ~90\% complete to M_r=-18.0. We find that in high-density regions ~70 per cent of galaxies are passively evolving independent of luminosity. In the rarefied field, however, the fraction of passively evolving galaxies is a strong function of luminosity, dropping from 50 per cent for Mr <~ -21 to zero by Mr ~ -18. Moreover the few passively evolving dwarf galaxies in field regions appear as satellites to bright (>~ L*) galaxies. Moreover the fraction of galaxies with the optical signatures of an active galactic nucleus (AGN) decreases steadily from ~50\% at Mr~-21 to ~0 per cent by Mr~-18 closely mirroring the luminosity dependence of the passive galaxy fraction in low-density environments (see fig. 1 continuous lines). This result reflects the increasing importance of AGN feedback with galaxy mass for their evolution, such that the star formation histories of massive galaxies are primarily determined by their past merger history.
We present high resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4 fine-structure lines are detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and a relatively low UV radiation field (GO = 10^2). The remaining gas is predominantly found in clouds with higher densities (n=10^5 cm^-3) and radiation fields (GO = 10^2.75), but somewhat lower column densities (N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n=10^6 cm^-3) and UV field (GO = 10^3.25). These results show the strength of multi-component modeling for the interpretation of the integrated properties of galaxies.
The radio surface brightness-to-diameter ({\Sigma} - D) relation for supernova remnants (SNRs) in the starburst galaxy M82 is analyzed in a statistically more robust manner than in the previous studies that mainly discussed sample quality and related selection effects. The statistics of data fits in log {\Sigma} - log D plane are analyzed by using vertical (standard) and orthogonal regressions. As the parameter values of D - {\Sigma} and {\Sigma} - D fits are invariant within the estimated uncertainties for orthogonal regressions, slopes of the empirical {\Sigma} - D relations should be determined by using the orthogonal regression fitting procedure. Thus obtained {\Sigma} - D relations for samples which are not under severe influence of the selection effects could be used for estimating SNR distances. Using the orthogonal regression fitting procedure {\Sigma} - D slope {\beta} \approx 3.9 is obtained for the sample of 31 SNRs in M82. The results of implemented Monte Carlo simulations show that the sensitivity selection effect does not significantly influence the slope of M82 relation. This relation could be used for estimation of distances to SNRs that evolve in denser interstellar environment, with number denisty up to 1000 particles per cm3 .
We present a simple model of inflation that can produce arbitrarily large spherical underdense or overdense regions embedded in a standard Lambda cold dark matter paradigm, which we refer to as bubbles. We analyze the effect such bubbles would have on the Cosmic Microwave Background (CMB). For super-horizon sized bubble in the vicinity of the last scattering surface, a signal is imprinted onto CMB via a combination of Sach-Wolfe and an early integrated Sach-Wolfe (ISW) effects. Smaller, sub-horizon sized bubbles at lower redshifts (during matter domination and later) can imprint secondary anisotropies on the CMB via Rees-Sciama, late-time ISW and Ostriker-Vishniac effects. Our model, and arguably most similar inflationary models, produce bubbles which are over/underdense in potential: in density such bubbles are characterized by having a distinct wall with the interior staying at the cosmic mean density. We show that such models can, with only moderate fine tuning, explain the \emph{cold spot}, a non-Gaussian feature identified in the Wilkinson Microwave Anisotropy Probe (WMAP) data by several authors.
We study the relationship between the metallicity of gamma-ray burst (GRB) progenitors and the probability distribution function (PDF) of GRB host galaxies as a function of luminosity using cosmological hydrodynamic simulations of galaxy formation. We impose a maximum limit to the gas metallicity in which GRBs can occur, and examine how the predicted luminosity PDF of GRB host galaxies changes in the simulation. We perform the Kolmogorov-Smirnov test, and show that the result from our simulation agrees with the observed luminosity PDF of core-collapse supernovae (SNe) host galaxies when we assume that the core-collapse SNe trace star formation. When we assume that GRBs occur only in a low-metallicity environment with $Z\lesssim 0.1 \Zsun$, GRBs occur in lower luminosity galaxies, and the simulated luminosity PDF becomes quantitatively consistent with the observed luminosity PDF. The observational bias against the host galaxies of optically dark GRBs owing to dust extinction may be another reason for the lower luminosities of GRB host galaxies, but the observed luminosity PDF of GRB host galaxies cannot be reproduced solely by the dust bias in our simulation.
We propose a postulate $\dot{q} =MH$ for temporal variation of quintessence field $q$ where $H$ is Hubble parameter ($=\dot{a}/a$) and $M$ is the scale of $q$. The postulate uniquely determines a dynamical model of the field. We show that the total energy density of matter and the field vanishes as spatial scale factor $a$ becomes infinite. We also show that the tiny dark energy today is caused by early inflation. Since the model is reduced to $\Lambda$CDM model in the limit $M\to 0$, it is a natural extension of $\Lambda$CDM model.
In this work, we present an analysis of a data cube obtained with the instrument IFU/GMOS Gemini North telescope centered on the nuclear region of the LINER galaxy NGC 4579. This galaxy is known to have a type 1 AGN (see Eracleous et al. 2002 for a review). The methodology used for the analysis of the data cube was PCA tomography (Steiner et al. 2009), which consists of applying the statistical tool known as principal component analysis (PCA) to extract information from data cubes.
We perform a detailed phase-space analysis of k-essence cosmology. We find the critical points can be divided into three classes: points unstable but model stable, both point and model stable, points stable but model unstable. Like points unstable but model stable, points stable but model unstable are not relevant from a cosmological point of view, though they can be late-time attractors for the universe. So in order to study the possible final state of the universe, it is important to investigate not only the stability of the critical points but also the stability of the model. Both point and model stable can further be divided into two classes: points only presenting decelerating phases and points at which all decelerating, constant-speed, and accelerating phases can appear; the final state of the universe dependents on the potential.
Ultra high energy cosmic rays (UHECRs), with energies above ~6 x 10^19 eV, seem to show a weak correlation with the distribution of matter relatively near to us in the universe. It has earlier been proposed that UHECRs could be accelerated in either the nucleus or the outer lobes of the nearby radio galaxy Cen A. We show that UHECR production at a spatially intermediate location about 15 kpc northeast from the nucleus, where the jet emerging from the nucleus is observed to strike a large star-forming shell of gas, is a plausible alternative. A relativistic jet is capable of accelerating lower-energy heavy seed cosmic rays (CRs) to UHECRs on timescales comparable to the time it takes the jet to pierce the large gaseous cloud. In this model many CRs arising from a starburst, with a composition enhanced in heavy elements near the knee region around PeV, are boosted to ultra-high energies by the relativistic shock of a newly oriented jet. This model matches the overall spectrum shown by the Auger data and also makes a prediction for the chemical composition as a function of particle energy. We thus predict an observable anisotropy in the composition at high energy in the sense that lighter nuclei should preferentially be seen toward the general direction of Cen A. Taking into consideration the magnetic field models for the Galactic disk and a Galactic magnetic wind, this scenario may resolve the discrepancy between HiRes and Auger results concerning the chemical composition of UHECRs.
In the pursuit of a general formulation for a modified gravitational theory at the non-relativistic level and as an alternative to the dark matter hypothesis, we construct a model valid over a wide variety of astrophysical scales. We show how, through the inclusion of Milgrom's acceleration constant into a gravitational theory, that very general formulas can be constructed for the acceleration felt by a particle. Dimensional analysis shows that this inclusion naturally leads to the appearance of a mass-length scale in gravity, breaking its scale invariance. A particular form of the modified gravitational force is constructed and tested for consistency with observations over a wide range of astrophysical environments, from solar system to extragalactic scales. We show that over any limited range of physical parameters, which define any given class of astrophysical objects, the dispersion velocity of a system must be a power law of its mass and size. These powers appear linked together through a consistency relation of the theory. This yields a generalised gravitational equilibrium relation valid for all astrophysical systems. In particular, we show that the fundamental plane of elliptical galaxies, the Newtonian virial equilibrium, the Tully-Fisher relation and the scalings observed in local dwarf spheroidal galaxies, are nothing but particular cases of that relation when applied to the appropriate mass-length scales. Also, an operational equivalence to MOND and a working prescription for the construction of N-body codes in any modified non-relativistic gravitation theory are given. We discuss the implications of this approach for a modified theory of gravity and emphasise the advantages of working with the force instead of the dynamical part in the formulation of a gravitational theory.
The six-meter Atacama Cosmology Telescope (ACT) in Chile was built to measure the cosmic microwave background (CMB) at arcminute angular scales. We are building a new polarization sensitive receiver for ACT (ACTPol). ACTPol will characterize the gravitational lensing of the CMB and aims to constrain the sum of the neutrino masses with ~0.05 eV precision, the running of the spectral index of inflation-induced fluctuations, and the primordial helium abundance to better than 1%. Our observing fields will overlap with the SDSS BOSS survey at optical wavelengths, enabling a variety of cross-correlation science, including studies of the growth of cosmic structure from Sunyaev-Zel'dovich observations of clusters of galaxies as well as independent constraints on the sum of the neutrino masses. We describe the science objectives and the initial receiver design.
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We have reanalyzed the images of nearby red-sequence galaxies in the Sloan Digital Sky Survey, and have carefully selected 1,923 elliptical galaxies with velocity dispersion sigma>70 km/s and at redshifts z<0.05. Elliptical galaxies are the dominant population at high luminosities (>~ L^{\ast}) and the highest velocity dispersion ellipticals favor high-density environments. The average spectra depend strongly on sigma: they are much bluer and have stronger (but still weak) emission lines at low sigma. At fixed sigma, the average spectra also depend on environment, though less so. We show for the first time that field elliptical galaxies have a slightly bluer stellar continuum, especially at wavelengths <~ 4000 AA, and have stronger (but still weak) emission lines than their group counterparts. We also study the stellar populations using Lick index measurements. At a given sigma, elliptical galaxies in groups have systematically weaker Balmer absorption than their field counterparts. We find no clear environmental dependence of <Fe>, and the alpha-element absorption indices such as Mg b are only slightly stronger in rich group galaxies. An analysis based on simple stellar populations (SSPs) reveals a strong sigma dependence of SSP age, metallicity and alpha-abundance: more massive elliptical galaxies are older, more metal-rich and more strongly alpha-enhanced. On average, the SSP-equivalent ages of galaxies in rich groups are ~ 1 Gyr older than that of their field counterparts. We also find that galaxies in rich groups are slightly more metal-poor (in terms of [Fe/H]) and slightly more strongly alpha-enhanced, but only at a barely detectable level. Our analyses of the average spectra and the Lick indices are consistent with stronger low-level recent star formation in field ellipticals, similar to recent results based on ultraviolet and infrared observations. (Abridged)
Taking into account noise from intrinsic ellipticities of source galaxies, in this paper, we study the peak statistics in weak-lensing convergence maps around clusters of galaxies and beyond. We emphasize how the noise peak statistics is affected by the density distribution of nearby clusters, and also how cluster-peak signals are changed by the existence of noise. These are the important aspects to be understood thoroughly in weak-lensing analyses for individual clusters as well as in cosmological applications of weak-lensing cluster statistics. We adopt Gaussian smoothing with the smoothing scale $\theta_G=0.5\hbox{ arcmin}$ in our analyses. It is found that the noise peak distribution near a cluster of galaxies depends sensitively on the density profile of the cluster. For a cored isothermal cluster with the core radius $R_c$, the inner region with $R\le R_c$ appears noisy containing on average $\sim 2.4$ peaks with $\nu\ge 5$ for $R_c= 1.7\hbox{ arcmin}$ and the true peak height of the cluster $\nu=5.6$, where $\nu$ denotes the convergence signal to noise ratio. For a NFW cluster of the same mass and the same central $\nu$, the average number of peaks with $\nu\ge 5$ within $R\le R_c$ is $\sim 1.6$. Thus a high peak corresponding to the main cluster can be identified more cleanly in the NFW case. In the outer region with $R_c<R\le 5R_c$, the number of high noise peaks is considerably enhanced in comparison with that of the pure noise case without the nearby cluster. (abridged)
We present optical and X-ray properties for the first confirmed galaxy cluster sample selected by the Sunyaev-Zel'dovich Effect from 148 GHz maps over 455 square degrees of sky made with the Atacama Cosmology Telescope. These maps, coupled with multi-band imaging on 4-meter-class optical telescopes, have yielded a sample of 23 galaxy clusters with redshifts between 0.118 and 1.066. Of these 23 clusters, 10 are newly discovered. The selection of this sample is approximately mass limited and essentially independent of redshift. We provide optical positions, images, redshifts and X-ray fluxes and luminosities for the full sample, and X-ray temperatures of an important subset. The mass limit of the full sample is around 8e14 Msun, with a number distribution that peaks around a redshift of 0.4. For the 10 highest significance SZE-selected cluster candidates, all of which are optically confirmed, the mass threshold is 1e15 Msun and the redshift range is 0.167 to 1.066. Archival observations from Chandra, XMM-Newton, and ROSAT provide X-ray luminosities and temperatures that are broadly consistent with this mass threshold. Our optical follow-up procedure also allowed us to assess the purity of the ACT cluster sample. Eighty (one hundred) percent of the 148 GHz candidates with signal-to-noise ratios greater than 5.1 (5.7) are confirmed as massive clusters. The reported sample represents one of the largest SZE-selected sample of massive clusters over all redshifts within a cosmologically-significant survey volume, which will enable cosmological studies as well as future studies on the evolution, morphology, and stellar populations in the most massive clusters in the Universe.
We consider the problem of multifrequency VLBA image synthesis and spectral-index mapping for active galactic nuclei related to the necessity of taking into account the frequency-dependent image shift. We describe our generalized multifrequency synthesis algorithm with a spectral correction based on the maximum entropy method. The results of our processing of multifrequency VLBI data for the radio sources J2202+4216, J0336+3218, and J1419+5423 are presented.
We present a compilation of properties of the 105,783 quasars in the SDSS Data Release 7 (DR7) quasar catalog. In this value-added product, we compile continuum and emission line measurements around the Halpha, Hbeta, MgII and CIV regions, as well as other quantities such as radio properties, broad absorption line quasar (BALQSO) flags, and disk emitters. We also compile virial black hole mass estimates based on various calibrations. For the fiducial virial mass estimates we use the Vestergaard & Peterson (VP06) calibrations for Hbeta and CIV, and our own calibration for MgII which matches the VP06 Hbeta masses on average. We describe the construction of this catalog, and discuss its limitations. The catalog and its future updates will be made publicly available online.
The observed dark energy phenomenon is attributed to the presence of the zero-point fluctuations of matter fields. We show that due to the presence of the gas of virtual wormholes the zero-point energy is finite and forms the finite (of the Planckian order) value. The observed value of the cosmological constant is somewhat reduced due to the two effects. First is the renormalization of the gravitational constant which presumably forms the initial (local) value $H^2_{inf}$ predicted by the inflationary scenario. And second is an additional reduction due to the presence of the gas of actual wormholes required by the dark matter phenomenon. We show that the Starobinsky model of inflation explains both, the inflationary stage in the past and the present day acceleration of the Universe. It also represents the so-called model of the eternal Universe.
The first stars to form in the history of the universe may have been powered by dark matter annihilation rather than by fusion. This new phase of stellar evolution may have lasted millions to billions of years. These dark stars can grow to be very large, > 10^5 solar masses, and are relatively cool (~10^4 K). They are also very bright, being potentially detectable in the upcoming James Webb Space Telescope or even the Hubble Space Telescope. Once the dark matter runs out, the dark stars have a short fusion phase, before collapsing into black holes (BH). The resulting BH could serve as seeds for the (unexplained) supermassive black holes at high redshift and at the centers of galaxies.
The evolutionary stage of a powerful radio source originated by an AGN is related to its linear size. In this context, compact symmetric objects (CSOs), which are powerful and intrinsically small (< 1 kpc) radio sources with a convex synchrotron radio spectrum that peaks around the GHz regime, should represent a young stage in the individual radio source life. Their radio jets expand within the dense and inhomogeneous interstellar medium of the host galaxy, which may influence the source growth. The radio emission is expected to evolve as a consequence of adiabatic expansion and radiative and inverse Compton losses. The role played by the different mechanisms in the radio and gamma regimes is discussed.
Inflationary cosmology is the leading explanation of the very early universe. Many different models of inflation have been constructed which fit current observational data. In this work theoretical and numerical methods for constraining the parameter space of a wide class of such models are described. First, string-theoretic models with large non-Gaussian signatures are investigated. An upper bound is placed on the amplitude of primordial gravitational waves produced by ultra-violet Dirac-Born-Infeld inflation. In all but the most finely tuned cases, this bound is incompatible with a lower bound derived for inflationary models which exhibit a red spectrum and detectable non-Gaussianity. By analysing general non-canonical actions, a class of models is found which can evade the upper bound when the phase speed of perturbations is small. The multi-coincident brane scenario with a finite number of branes is one such model. For models with a potentially observable gravitational wave spectrum the number of coincident branes is shown to take only small values. The second method of constraining inflationary models is the numerical calculation of second order perturbations for a general class of single field models. The Klein-Gordon equation at second order, written in terms of scalar field variations only, is numerically solved. The slow roll version of the second order source term is used and the method is shown to be extendable to the full equation. This procedure allows the evolution of second order perturbations in general and the calculation of the non-Gaussianity parameter in cases where there is no analytical solution available.
In these proceedings, we discuss the extraction, in WMAP 5 year data, of a clean CMB map, of foreground emission (dominated by emission of the interstellar medium of our galaxy), and of the tiny signal from Sunyaev Zel'dovich effect in the direction of known galaxy clusters. The implementation of an Internal Linear Combination method locally in both pixel and harmonic space, with the use of a decomposition of WMAP maps onto a frame of spherical needlets, permits to extract a full sky CMB map, with good accuracy even in regions close to the galactic plane. Proper subtraction of this estimated CMB from WMAP original observations provides us with CMB-free foreground maps, which can be used for the analysis of the emission of the galactic interstellar medium and for detecting and measuring emissions from compact sources. Finally, while the Sunyaev-Zel'dovich cannot be detected for individual clusters in WMAP data, due to lack of spatial resolution and sensitivity, a stacking analysis of tentative detections towards a number of known ROSAT clusters permits to detect the SZ effect in WMAP data and measure how the SZ flux scales with cluster mass and X-ray luminosity.
We study the impact of ultra-violet background radiation field (UVB) and the local stellar radiation on the H_I column density distribution f(N_HI) of damped Lyman-alpha systems (DLAs) and sub-DLAs at z=3 using cosmological smoothed particle hydrodynamics simulations. We find that, in the previous simulations with an optically thin approximation, the UVB was sinking into the H_I cloud too deeply, and therefore we underestimated the f(N_HI) at 19 < log(N_HI) < 21.2 compared to the observations. When the UVB is shut off in the high-density regions with n_gas > 6 x 10^{-3} cm^{-3}, then we reproduce the observed f(N_HI) at z=3 very well. We also investigate the effect of local stellar radiation by post-processing our simulation with a radiative transfer code, and find that the local stellar radiation reduces the f(N_HI) by a factor of ~0.7, which further improves the agreement with the observation. Our results show that the shape of f(N_HI) is determined primarily by the treatment of UVB, with a weaker effect by the local stellar radiation, and that the optically thin approximation often used in cosmological simulation is inadequate to properly treat the ionization structure of neutral gas in and out of DLAs.
We present results from a WIYN 3.5m telescope imaging study of the globular cluster (GC) systems of the edge-on spiral galaxies NGC891 and NGC4013. We used the 10' x 10' Minimosaic Imager to observe the galaxies in BVR filters to projected radii of ~20 kpc from the galaxy centers. We combined the WIYN data with archival and published data from WFPC2 and ACS on the Hubble Space Telescope to assess the contamination level of the WIYN GC candidate sample and to follow the GC systems further in toward the galaxies' centers. We constructed radial distributions for the GC systems using both the WIYN and HST data. The GC systems of NGC891 and NGC4013 extend to 9+/-3 kpc and 14+/-5 kpc, respectively, before falling off to undetectable levels in our images. We use the radial distributions to calculate global values for the total number (N_GC) and specific frequencies (S_N and T) of GCs. NGC4013 has N_GC = 140+/-20, S_N = 1.0+/-0.2 and T = 1.9+/-0.5; our N_GC value is ~40% smaller than a previous determination from the literature. The HST data were especially useful for NGC891, because the GC system is concentrated toward the plane of the galaxy and was only weakly detected in our WIYN images. Although NGC891 is thought to resemble the Milky Way in its overall properties, it has only half as many GCs, with N_GC = 70+/-20, S_N = 0.3+/-0.1 and T = 0.6+/-0.3. We also calculate the galaxy-mass-normalized number of blue (metal-poor) GCs in NGC891 and NGC4013 and find that they fall along a general trend of increasing specific frequency of blue GCs with increasing galaxy mass. Given currently available resources, the optimal method for studying the global properties of extragalactic GC systems is to combine HST data with wide-field, ground-based imaging with good resolution. The results here demonstrate the advantage gained by using both methods when possible.
We review the current theory of how galaxies form within the cosmological framework provided by the cold dark matter paradigm for structure formation. Beginning with the pre-galactic evolution of baryonic material we describe the analytical and numerical understanding of how baryons condense into galaxies, what determines the structure of those galaxies and how internal and external processes (including star formation, merging, active galactic nuclei etc.) determine their gross properties and evolution. Throughout, we highlight successes and failings of current galaxy formation theory. We include a review of computational implementations of galaxy formation theory and assess their ability to provide reliable modeling of this complex phenomenon. We finish with a discussion of several "hot topics" in contemporary galaxy formation theory and assess future directions for this field.
To derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M82 and NGC253. We present high sensitivity observations of CCH and two of its 13C isotopologues, C13CH and 13CCH, as well as the optically thin emission from C18O and 13C18O. We assume the column density ratio between isotopologues is representative of the 12C13C isotopic ratio. From CCH, lower limits to the 12C/13C isotopic ratio of 138 in M82, and 81 in NGC253, are derived. Lower limits to the 12C/13C ratios from CO isotopologues support these. 13C18O is tentatively detected in NGC253, which is the first reported detection in the extragalactic ISM. Based on these limits, we infer ratios of 16O/18O>350 and >300 in M82 and NGC253, respectively, and 32S/34S>16 in NGC253. and the H2 column density determination through the optically thin tracers 13CO and C18O. The derived CCH fractional abundances toward these galaxies of <~1.1\times10^-8 are in good agreement with those of molecular clouds in the Galactic disk. Our lower limits to the 12C/13C ratio from CCH are a factor of 2-3 larger than previous limits. The results are discussed in the context of molecular and nucleo-chemical evolution. The large 12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.
We perform the analysis of the trispectrum of curvature perturbations generated by the interactions characterizing a general theory of single-field inflation obtained by effective field theory methods. We find that curvature-generated interaction terms, which can in general give an important contribution to the amplitude of the four-point function, show some new distinctive features in the form of their trispectrum shape-function. These interesting interactions are invariant under some recently proposed symmetries of the general theory and, as shown explicitly, do allow for a large value of the trispectrum.
We develop a new numerical approach to describe the action of ram pressure stripping (RPS) within a semi-analytic model of galaxy formation and evolution which works in combination with non-radiative hydrodynamical simulations of galaxy clusters. The new feature in our method is the use of the gas particles to obtain the kinematical and thermodynamical properties of the intragroup and intracluster medium (ICM). This allows a self-consistent estimation of the RPS experienced by satellite galaxies. We find that the ram pressure (RP) in the central regions of clusters increases approximately one order of magnitude between z = 1 and 0, consistent with the increase in the density of the ICM. The mean RP experienced by galaxies within the virial radius increases with decreasing redshift. In clusters with virial masses M_vir ~10^15 h^-1 M_Sun, over 50% of satellite galaxies have experienced RP ~10^(-11) h^-2 dyn cm^-2 or higher for z <= 0.5. In smaller clusters (M_vir ~10^14 h^-1 M_Sun) the mean RP are approximately one order of magnitude lower at all redshifts. RPS has a strong effect on the cold gas content of galaxies for all cluster masses. At z = 0, over 70% of satellite galaxies within the virial radius are completely depleted of cold gas. For the more massive clusters the fraction of depleted galaxies is already established at z ~ 1, whereas for the smaller clusters this fraction increases appreciably between z = 1 and 0. This indicates that the rate at which the cold gas is stripped depends on the virial mass of the host cluster. Compared to our new approach, the use of an analytic profile to describe the ICM results in an overestimation of the RP larger than 50% for z >= 0.5.
We show that the cosmological phase transition from the first accelerated expansion in the early universe to the second accelerated expansion over the intermediate decelerated expansion is possible in the HL gravity without the ``detailed balance'' condition if the dark scalar energy density is assumed to be negative. Moreover, we obtain various evolutions depending on the scale factor and the expansion rate. Finally, we discuss the existence of the minimum scale in connection with the singularity free condition.
Starting as highly relativistic collimated jets, gamma-ray burst outflows gradually decelerate and become non-relativistic spherical blast waves. Although detailed analytical solutions describing the afterglow emission received by an on-axis observer during both the early and late phases of the outflow evolution exist, a calculation of the received flux during the intermediate phase and for an off-axis observer requires either a more simplified analytical model or direct numerical simulations of the outflow dynamics. In this paper we present light curves for off-axis observers covering the long-term evolution of the blast wave calculated from a high resolution two-dimensional relativistic hydrodynamics simulation using a synchrotron radiation model. We compare our results to earlier analytical work and calculate the consequence of the observer angle with respect to the jet axis both for the detection of orphan afterglows and for jet break fits to the observational data. We find that observable jet breaks can be delayed for up to several weeks for off-axis observers, potentially leading to overestimation of the beaming corrected total energy. When using our off-axis light curves to create synthetic Swift X-ray data, we find that jet breaks are likely to remain hidden in the data. We also confirm earlier results in the literature finding that only a very small number of local Type Ibc supernovae can harbor an orphan afterglow.
We study the tensor perturbations in a class of non-local, purely gravitational models which naturally end inflation in a distinctive phase of oscillations with slight and short violations of the weak energy condition. We find the usual generic form for the tensor power spectrum. The presence of the oscillatory phase leads to an enhancement of gravitational waves with frequencies somewhat less than 10^{10} Hz.
We have used the expansion process of hot milk, which has similarities with the cosmic expansion, to facilitate easier and better visualization and teaching of cosmological concepts. Observations of the milk are used to illustrate phenomena related to the Planck era, the standard hot big bang model, cosmic inflation, problems with the formation of structure, and other subjects. This innovative and easily implemented demonstration can enhance the learning of cosmological concepts.
Based on the formulation of the reconstruction for the k-essence model, which was recently proposed in arXiv:1001.0220 [hep-th], we explicitly construct cosmological model to unifying the late-time acceleration and the inflation in the early universe.
Ground-based gamma-ray astronomy, which provides access to the TeV energy range, is a young and rapidly developing discipline. Recent discoveries in this waveband have important consequences for a wide range of topics in astrophysics and astroparticle physics. This article is an attempt to review the experimental status of this field and to provide the basic formulae and concepts required to begin the interpretation of TeV observations.
Many experiments seek dark matter by detecting relatively low energy nuclear recoils. Yet since events from ordinary physics with energies in the 1-100 KeV range are commonplace, all claims of signals or their absence hinge on exhaustive calibrations and background rejection. We document many curious and consistent discrepancies between the backgrounds which neutrons can produce versus the picture of neutrons and claims of neutron calibration found in dark matter literature. Much of the actual physics of neutrons is either under-recognized or under-reported, opening up new interpretations of current data. All signals seen so far, including those presented tentatively such as CoGENT, or the bold claims and time dependence of DAMA/LIBRA, appear to be consistent with neutron-induced backgrounds. At the same time it is the burden of proof of experimental groups to support their claims no possible background could matter, not ours. The existing hypotheses about backgrounds stated by experiments, accepted at face value and as published, make possible a variety of neutron-induced events to be registered as dark matter signals.
We present the hardware and software systems implementing autonomous
operation, distributed real-time monitoring, and control for the EBEX
instrument. EBEX is a NASA-funded balloon-borne microwave polarimeter designed
for a 14 day Antarctic flight that circumnavigates the pole.
To meet its science goals the EBEX instrument autonomously executes several
tasks in parallel: it collects attitude data and maintains pointing control in
order to adhere to an observing schedule; tunes and operates up to 1920 TES
bolometers and 120 SQUID amplifiers controlled by as many as 30 embedded
computers; coordinates and dispatches jobs across an onboard computer network
to manage this detector readout system; logs over 3~GiB/hour of science and
housekeeping data to an onboard disk storage array; responds to a variety of
commands and exogenous events; and downlinks multiple heterogeneous data
streams representing a selected subset of the total logged data. Most of the
systems implementing these functions have been tested during a recent
engineering flight of the payload, and have proven to meet the target
requirements.
The EBEX ground segment couples uplink and downlink hardware to a
client-server software stack, enabling real-time monitoring and command
responsibility to be distributed across the public internet or other standard
computer networks. Using the emerging dirfile standard as a uniform
intermediate data format, a variety of front end programs provide access to
different components and views of the downlinked data products. This
distributed architecture was demonstrated operating across multiple widely
dispersed sites prior to and during the EBEX engineering flight.
Precision cosmology and big-bang nucleosynthesis mildly favor extra radiation in the universe beyond photons and ordinary neutrinos, lending support to the existence of low-mass sterile neutrinos. We use the WMAP 7-year data release, small-scale CMB observations from ACBAR, BICEP and QuAD, the 7th data release of the Sloan Digital Sky Survey, and measurement of the Hubble parameter from Hubble Space Telescope observations to derive credible regions for the assumed common mass scale m_s and effective number N_s of thermally excited sterile neutrino states. Our results are compatible with the interpretation of the LSND and MiniBooNE anomalies in terms of 3 active + 2 sterile neutrinos if m_s is in the sub-eV range.
We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found. The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic latitudes (|b| >= 10^\circ). At low galactic latitudes (|b| <= 10^\circ) most of unidentified X-ray sources (~94%) lie at |b| <= 2^\circ. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties. These tables are intended as a useful tool for researchers interested in particular identifications.
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We use measurements of the HI content, stellar mass and star formation rates in ~190 massive galaxies with stellar masses greater than 10^10 Msun, obtained from the Galex Arecibo SDSS Survey (GASS) described in Paper I (Catinella et al. 2010) to explore the global scaling relations associated with the bin-averaged ratio of the star formation rate over the HI mass, which we call the HI-based star formation efficiency (SFE). Unlike the mean specific star formation rate, which decreases with stellar mass and stellar mass surface density, the star formation efficiency remains relatively constant across the sample with a value close to SFE = 10^-9.5 yr^-1 (or an equivalent gas consumption timescale of ~3 Gyr). Specifically, we find little variation in SFE with stellar mass, stellar mass surface density, NUV-r color and concentration. We interpret these results as an indication that external processes or feedback mechanisms that control the gas supply are important for regulating star formation in massive galaxies. An investigation into the detailed distribution of SFEs reveals that approximately 5% of the sample shows high efficiencies with SFE > 10^-9 yr^-1, and we suggest that this is very likely due to a deficiency of cold gas rather than an excess star formation rate. Conversely, we also find a similar fraction of galaxies that appear to be gas-rich for their given specific star-formation rate, although these galaxies show both a higher than average gas fraction and lower than average specific star formation rate. Both of these populations are plausible candidates for "transition" galaxies, showing potential for a change (either decrease or increase) in their specific star formation rate in the near future. We also find that 36+/-5% of the total HI mass density and 47+/-5% of the total SFR density is found in galaxies with stellar mass greater than 10^10 Msun. [abridged]
(Abridged) The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were analyzed to derive the intrinsic shape of their bulges. We developed a new method to derive the intrinsic shape of bulges based on the geometrical relationships between the apparent and intrinsic shapes of bulges and disks. The equatorial ellipticity and intrinsic flattening of bulges were obtained from the length of the apparent major and minor semi-axes of the bulge, twist angle between the apparent major axis of the bulge and the galaxy line of nodes, and galaxy inclination. We found that the intrinsic shape is well constrained for a subsample of 115 bulges with favorable viewing angles. A large fraction of them is characterized by an elliptical section (B/A<0.9). This fraction is 33%, 55%, and 43% if using their maximum, mean, or median equatorial ellipticity, respectively. Most are flattened along their polar axis (C<(A+B)/2). The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sersic index n>2, or equivalently, by the bulges of galaxies with a bulge-to-total ratio B/T>0.3. In particular, bulges with n\leq2 and with B/T\leq0.3 show a larger fraction of oblate axisymmetric (or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to bulges with n>2 and with B/T>0.3, respectively. According to predictions of the numerical simulations of bulge formation, bulges with n\leq2, which show a high fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have B/T\leq0.3, could be the result of dissipational minor mergers. Both major dissipational and dissipationless mergers seem to be required to explain the variety of shapes found for bulges with n>2 and B/T>0.3.
Extended extragalactic radio sources have traditionally been classified into FR I and II types, based on the ratio r of the separation S between the brightest regions on either sides of the host galaxy and the total size T of the radio source. Here we examine the distribution of various physical properties as a function of r of 1045 luminous radio galaxies (RGs) at z<0.3 from the SDSS, NVSS, and FIRST. About 2/3 of the RGs are lobe-dominated (LD), and 1/3 have prominent jets. If we follow the original definition of the FR types (a division based solely on r), FR I and FR II RGs overlap in their host galaxy properties. However, the rare, LD sources with r>0.8 AND OIII5007 line luminosity >10^6 Lsun are markedly different on average from the rest of the RGs, in the sense that they are hosted in lower mass galaxies, live in relatively sparse environments, and have higher accretion rates onto the central SMBH. Thus these objects and the rest of RGs form a well-defined dichotomy. Motivated by the stark differences in the nuclear emission line properties of the RG subsamples, we suggest that the accretion rate onto the SMBH may play the primary role in creating the different morphologies. At relatively high accretion rates, the accretion system may produce powerful jets that create the "classical double" morphology (roughly corresponding to the LD sources with r>0.8 and emission lines); at lower accretion rates the jets from a radiatively inefficient accretion flow generate radio lobes without apparent "hot spots" at the edge (corresponding to the majority of LD sources). At slightly lower accretion rates AND in galaxies with dense galactic structure, sources with prominent jets result. It is possible that while the high accretion rate systems could affect sub-Mpc scale environments, the jets from lower accretion rate systems may efficiently suppress activity within the host galaxies.
With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey (NMBS), we study the stellar populations of the oldest and most massive galaxies (>10^11 Msun) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected U-V colors out to z=2.2, with accurate photometric redshifts, sigma_z/(1+z)~2%, and rest-frame colors, sigma_U-V~0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame U-V colors of quiescent galaxies with redshift. This scatter in color arises from the spread in ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies towards higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000A- and Balmer-breaks, respectively. Some of the quiescent galaxies may be up to 4 times older than the average age- and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed U-V color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies towards higher redshift, red mergers at z<1, and a frosting of relatively young stars from star formation at later times.
Increasingly large samples of galaxies are now being discovered at redshifts z~5-6 and higher. Many of these objects are inferred to be young, low in mass, and relatively unreddened, but detailed analysis of their high quality spectra will not be possible until the advent of future facilities. In this paper we shed light on the physical conditions in a plausibly similar low mass galaxy by presenting the analysis of the rest-frame optical and UV spectra of Q2343-BX418, an L* galaxy at z=2.3 with a very low mass-to-light ratio and unusual properties: BX418 is young (<100 Myr), low mass (M_star ~ 10^9 Msun), low in metallicity (Z ~ 1/6 Zsun), and unreddened (E(B-V)~0.02, UV continuum slope beta=-2.1). We infer a metallicity 12+log(O/H)=7.9 +/- 0.2 from the rest-frame optical emission lines. We also determine the metallicity via the direct, electron temperature method, using the ratio O III] 1661, 1666/[O III] 5007 to determine the electron temperature and finding 12+ log(O/H)=7.8 +/- 0.1. These measurements place BX418 among the most metal-poor galaxies observed in emission at high redshift. The rest-frame UV spectrum contains strong emission from Lya (with rest-frame equivalent width 54 A), He II 1640 (both stellar and nebular), C III] 1907, 1909 and O III] 1661, 1666. The C IV/C III] ratio indicates that the source of ionization is unlikely to be an AGN. Analysis of the He II, O III] and C III] line strengths indicates a very high ionization parameter log U ~ -1, while Lya and the interstellar absorption lines indicate that outflowing gas is highly ionized over a wide range of velocities. It remains to be determined how many of BX418's unique spectral features are due to its global properties, such as low metallicity and dust extinction, and how many are indicative of a short-lived phase in the early evolution of an otherwise normal star-forming galaxy.
In 2004, Creminelli and Zaldarriaga proposed a consistency relation for the primordial curvature perturbation of all single-field inflation models; it related the bispectrum in the squeezed limit to the spectral tilt. However, their proof uses classical arguments whereas most bispectrum calculations use quantum field theory (via the in-in formalism, for example). We have applied similar arguments as Creminelli and Zaldarriaga to calculate the squeezed-limit primordial bispectrum using the in-in formalism and have arrived at a generic formula that does not rely on a slow-roll approximation and does not assume a particular vacuum state. We were not able to derive the consistency relation in all generality from this formula, though we did explicitly verify it for slow-roll inflation (a known result) and for power-law inflation (without employing any slow-roll approximation). Our technique could also be useful for other squeezed-limit calculations, e.g. for the single-field trispectrum or for the multi-field bispectrum. Our result also provides an interesting perspective on the \delta N-formalism: our final formula consists of one piece from a field redefinition and another piece from a quantum-field theory (in-in formalism) calculation; the field-redefinition piece exactly matches the single-field \delta N-formalism bispectrum in the squeezed limit.
The designs of the first generation of cosmological 21-cm observatories are split between a low-cost single dipole which integrates over the entire sky in order to find the global (spectral) signature of reionization, and interferometers with arcminute-scale angular resolution whose goal is to measure the 3D power spectrum of ionized regions during reionization. We examine whether intermediate scale instruments such as MWA 32T are capable of placing new constraints on reionization. We find that the global redshift of reionization can be measured from the variance in the 21-cm signal among multiple beams on large angular scales as a function of frequency, instead of the conventional approach of measuring the entire 21-cm power spectrum. The beam-to-beam variance in the differential brightness temperature peaks when the average neutral fraction was > 50%, providing a convenient flag of zreion. A low angular resolution of order 1 degree is needed to exploit the physical size of the ionized regions and maximize the signal-to-noise ratio. Thermal noise, foregrounds, and instrumental effects should be manageable, as long as the uv (Fourier) coverage is complete within the compact core required for low-resolution imaging. We find that zreion can potentially be detected to within a redshift uncertainty of 1 or better in 500 or more hours of integration on the existing MWA prototype (with only 32x16 dipoles), operating at an angular resolution of roughly 1 degree and a spectral resolution of 2.4 MHz. The prospects for such a detection are generic to similar 21-cm observatories (e.g., LOFAR) that have good uv coverage after earth-rotation synthesis for baselines corresponding to > roughly 1 degree.
We investigate whether stellar dust sources i.e. asymptotic giant branch (AGB) stars and supernovae (SNe) can account for dust detected in 5<z<6.5 quasars (QSOs). We calculate the required dust yields per AGB star and per SN using the dust masses of QSOs inferred from their millimeter emission and stellar masses approximated as the difference between the dynamical and the H_2 gas masses of these objects. We find that AGB stars are not efficient enough to form dust in the majority of the z>5 QSOs, whereas SNe may be able to account for dust in some QSOs. However, they require very high dust yields even for a top-heavy initial mass function. This suggests additional non-stellar dust formation mechanism e.g. significant dust grain growth in the interstellar medium of at least three out of nine z>5 QSOs. SNe (but not AGB stars) may deliver enough heavy elements to fuel this growth.
We investigate the use of MIR PAH bands, continuum and emission lines as probes of star-formation and AGN activity in a sample of 100 'normal' and local (z~0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer Space Telescope Infrared Spectrograph (IRS) as part of the Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) which includes multi-wavelength photometry from the UV to the FIR and optical spectroscopy. The continuum and features were extracted using PAHFIT (Smith et al. 2007), a decomposition code which we find to yield PAH equivalent widths up to ~30 times larger than the commonly used spline methods. Despite the lack of extreme objects in our sample (such as strong AGNs, low metallicity galaxies or ULIRGs), we find significant variations in PAH, continuum and emission line properties and systematic trends between these MIR properties and optically derived physical properties such as age, metallicity and radiation field hardness. We revisit the diagnostic diagram relating PAH equivalent widths and [Ne II]12.8micrometers/[O IV]25.9micrometers line ratios and find it to be in much better agreement with the standard optical star-formation/AGN classification than when spline decompositions are used, while also potentially revealing obscured AGNs. The luminosity of individual PAH components, of the continuum, and with poorer statistics, of the neon emission lines and molecular hydrogen lines, are found to be tightly correlated to the total IR luminosity, making individual MIR components good gauges of the total dust emission in SF galaxies. Like the total IR luminosity, these individual components can be used to estimate dust attenuation in the UV and in Halpha lines based on energy balance arguments. We also propose average scaling relations between these components and dust corrected, Halpha derived star-formation rates.
(abridged) Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of $\sim$16,000 independent regions, each with $\sim$1,000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. Excluding the 'X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift, or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions. We confirm the presence of a thick ($\sim$40 arcsec or $\sim$3 kpc) ring of high pressure gas at a radius of $\sim$180 arcsec ($\sim$14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M = 1.25. Another, younger shock-like feature is observed at a radius of $\sim$40 arcsec ($\sim$3 kpc) surrounding the central AGN, with an estimated Mach number M > 1.2. As shown previously, if repeated shocks occur every $\sim$10 Myrs, as suggested by these observations, then AGN driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350 - 400 arcsec (27 - 31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least $\sim1.0\times10^6$ solar masses of Fe has been lifted and deposited at a radius of 350-400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350 - 400 arcsec.
As the third paper of our serial studies that are aim at examining the AGN-host coevolution by using partially obscured AGNs, we extend the broad-line composite galaxies (composite AGNs) into ROSAT-selected Seyfert 1.8/1.9 galaxies basing upon the RASS/SDSS-DR5 catalog given by Anderson et al.. The SDSS spectra of in total 92 objects are analyzed by the same method used in our previous studies, after requiring the signal-to-noise ratio in the SDSS r' band is larger than 20. Combing the ROSAT-selected Seyfert galaxies with the composite AGNs reinforces the tight correlation between the line ratio [OI]/H\alpha vs. D_n(4000), and establishes a new tight correlation between [SII]/H\alpha vs. D_n(4000). Both correlations suggest the two line ratios are plausible age indicators of the circumnuclear stellar population for typical type I AGNs in which the stellar populations are difficult to be derived from their optical spectra. The ROSAT-selected Seyfert galaxies show that the two correlations depend on the soft X-ray spectral slope \alpha_X that is roughly estimated from the hardness ratios by requiring the X-ray count rates within 0.1-2.4 keV are larger than 0.02 counts s^-1. However, we fail to establish a relationship between \alpha_X and D_n(4000), which is likely caused by the relatively large uncertainties of both parameters (especially for \alpha_X because of the AGN intrinsic obscuration). The previously established L/L_Edd-D_n(4000) evolutionary sequence is reinforced again by the extension to the ROSAT-selected Seyfert galaxies. These X-ray-selected Seyfert galaxies are, however, biased against the two ends of the sequence, which implies that the X-ray Seyfert galaxies present a population at middle evolutionary stage.
Context. The high-redshift (z = 4.72) blazar J1430+4204 produced a major radio outburst in 2005. Such outbursts are usually associated with the emergence of a new component in the inner radio jet. Aims. We searched for possible changes in the radio structure on milli-arcsecond angular scales, to determine physical parameters that characterise the relativistic jet ejected from the centre of this source. Methods. We analysed 15-GHz radio interferometric images obtained with the Very Long Baseline Array (VLBA) before and after the peak of the outburst. Results. We did not identify any significant new jet component over a period of 569 days. We estimated the Doppler factor, the Lorentz factor, and the apparent transverse speed of a putative jet component using three different methods. The likely small jet angle to the line of sight and our values of the apparent transverse speed are consistent with not detecting a new jet feature.
We present new broad-band optical images of some merging Seyfert galaxies that were earlier considered to be non-interacting objects. On our deep images obtained at the Russian 6-m telescope we have detected elongated tidal envelopes belonging to satellites debris with a surface R-band brightness about 25-26.5 mag/arcsec^2. These structures are invisible in Sloan Digital Sky Survey (SDSS) pictures because of their photometric limit. We found that 35 per cent of the sample of isolated galaxies has undergone merging during the last 0.5-1 Gyr. Our results suggest that statistic studies based on popular imaging surveys (SDSS or Second Palomar Observatory Sky Survey (POSS-II)) can lead to underestimation of the fraction of minor mergers among galaxies with active nuclei (AGN). This fact impacts on statistics and must be taken into consideration when finding connection between minor/major merging or interactions and nucleus activity.
Studying Luminous InfraRed Galaxies (LIRGs) is particularly important in the build-up of the stellar mass from z=1 to z=0. We perform a multiwavelengths study of a LIRGs sample in the Extended Chandra Deep Field South at z=0.7, selected at 24 micrometers by MIPS onboard Spitzer Space Telescope and detected in 17 filters. Data go from the near-ultraviolet to the mid-infrared. This multiwavelengths dataset allows us to bring strong constraints on the spectral energy distributions (SEDs) of galaxies, and thus to efficiently derive physical parameters as the SFR, the total infrared luminosity, attenuation parameters and star formation history. An important part of this work is the elaboration of a mock catalogue which allows us to have a reliability criteria for the derived parameters. We study LIRGs by means of a SED-fitting code CIGALE. At first, this code creates synthetic spectra from the Maraston (2005) stellar population models. The stellar population spectra are being attenuated by using a synthetic Calzetti-based attenuation law before the addition of the dust emission as given by the infrared SED library of Dale&Helou (2002). The originality of CIGALE is that it allows us to perform consistent fits of the dust-affected ultaviolet-to-infrared wavelength range. This technique appears to be a very powerful tool in the case where we can have access to a dataset well-sampled over a large range of wavelengths. We are able to derive a star formation history and to estimate the fraction of infrared luminosity reprocessed by an active galactic nucleus. We study the dust temperatures of our galaxies detected at 70 \mu m and find them colder than predicted by models. We also study the relation between the SFR and the stellar mass and do not find a tight correlation between both, but a flat distribution and a large scatter which is interpreted in terms of variations of star formation history.
Direct detection of Weakly Interacting Massive Particle (WIMP) candidates of Dark Matter (DM) is studied within the context of a self-consistent truncated isothermal model of the finite-size dark halo of Milky Way in the light of the recent determination of the Galaxy's circular rotation curve out to 60 kpc. This new rotation curve declines with Galactocentric distance ($R$) for $R\gsim10\kpc$. Our Galaxy halo model takes into account the modifications of the phase-space structure of the dark matter halo due to the gravitational influence of the observed visible matter in a self-consistent manner. In contrast to the standard halo model (SHM) routinely used in analyzing the results of WIMP direct detection experiments, the velocity distribution of the WIMPs in our model is distinctly non-Maxwellian with a cut-off at a maximum velocity that is self-consistently determined by the model itself. For our halo model that provides the best fit to the new rotation curve data, the most stringent 90\% C.L. upper limit on the WIMP-nucleon spin-independent cross section from the recent results of the CDMS-II experiment, for example, is $\sim 5.3\times10^{-8}\pb$ for a WIMP mass of $\sim$ 71 GeV. We also find that there exists a range of small WIMP masses, typically $\sim$ 2 -- 10 GeV, within which DAMA collaboration's claimed annual modulation signal purportedly due to WIMPs is consistent with the null results of other experiments. For spin-dependent interaction the above upper WIMP mass range extends to about 16 GeV. Our results, based as they are on a self-consistent model of the dark matter halo of the Galaxy, the parameters of which are determined by a fit to the rotation curve of the Galaxy, strengthen the possibility of low-mass ($\lsim 10\gev$) WIMPs as a candidate for dark matter.
The `Internal Linear Combination' (ILC) component separation method has been extensively used on the data of the WMAP space mission, to extract a single component, the CMB, from the WMAP multifrequency data. We extend the ILC approach for reconstructing millimeter astrophysical emissions beyond the CMB alone. In particular, we construct a Constrained ILC to extract clean maps of both the CMB or the thermal Sunyaev Zeldovich (SZ) effect, with vanishing contamination from the other. The performance of the Constrained ILC is tested on simulations of Planck mission observations, for which we successfully reconstruct independent estimates of the CMB and of the thermal SZ.
The F -GAMMA program is a coordinated effort of several observing facilities to understand the AGN/blazar phenomenon via a multi-frequency monitoring approach, especially in the era of Fermi-GST. Some 60 prominent sources are monitored monthly with the Effelsberg 100-m telescope, the IRAM 30-m telescope and more frequently but in a less uniform fashion at the APEX 12-m telescope, covering from 2.64 to 345 GHz. The program has been running since January 2007 and here some of its findings are summarized. (a) There are two major variability patterns that the spectra of sources follow, one spectral-evolution-dominated and one achromatic. (b) The FSRQs show higher brightness temperatures indicative of larger Doppler factors at play and (c) a statistically significant radio-gamma-ray correlation has been found with a method recently suggested by Pavlidou et al. (in prep.).
We report the spectroscopic confirmation of SPT-CL J0546-5345 at <z> = 1.067. To date this is the most distant cluster to be spectroscopically confirmed from the 2008 South Pole Telescope (SPT) catalog, and indeed the first z > 1 cluster discovered by the Sunyaev-Zel'dovich Effect (SZE). We identify 21 secure spectroscopic members within 0.9 Mpc of the SPT cluster position, 18 of which are quiescent, early-type galaxies. From these quiescent galaxies we obtain a velocity dispersion of 1179^{+232}_{-167} km/s, ranking SPT-CL J0546-5345 as the most dynamically massive cluster yet discovered at z > 1. Assuming that SPT-CL J0546-5345 is virialized, this implies a dynamical mass of M_200 = 1.0^{+0.6}_{-0.4} x 10^{15} Msun, in agreement with the X-ray and SZE mass measurements. The spectroscopic confirmation of SPT-CL J0546-5345, discovered in the wide-angle, mass-selected SPT cluster survey, marks the onset of the high redshift SZE-selected galaxy cluster era.
We measure the evolution of galaxy clustering out to a redshift of z~1.5 using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S) and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift information to calculate the projected-angular correlation function, omega(sigma), from which we infer the projected correlation function Xi(sigma). We demonstrate that this technique delivers accurate measurements of clustering even when large redshift measurement errors affect the data. To this aim we use two mock MUSYC fields extracted from a LambdaCDM simulation populated with GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy of our estimates of Xi(sigma) and to identify and correct for systematic effects in our measurements. We study the evolution of clustering for volume limited subsamples of galaxies selected using their photometric redshifts and rest-frame r-band absolute magnitudes. We find that the real-space correlation length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered out to z~1.5, particularly for ECDF-S given its near-infrared photometric coverage. There is mild evidence for a luminosity dependent clustering in both fields at the low redshift samples (up to <z>=0.57), where the correlation length is higher for brighter galaxies by up to 1Mpc/h between median rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the photometric redshift measurement, each galaxy is assigned a best-fit template; we restrict to E and E+20%Sbc types to construct subsamples of early type galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift increases, making it unlikely (95% level) that ETGs at median redshift z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent passively evolved luminosities. (ABRIDGED)
In this paper we review a part of the approaches that have been considered to
explain the extraordinary discovery of the late time acceleration of the
Universe. We discuss the arguments that have led physicists and astronomers to
accept dark energy as the current preferable candidate to explain the
acceleration. We highlight the problems and the attempts to overcome the
difficulties related to such a component. We also consider alternative theories
capable of explaining the acceleration of the Universe, such as modification of
gravity. We compare the two approaches and point out the observational
consequences, reaching the sad but foresightful conclusion that we will not be
able to distinguish between a Universe filled by dark energy or a Universe
where gravity is different from General Relativity. We review the present
observations and discuss the future experiments that will help us to learn more
about our Universe. This is not intended to be a complete list of all the dark
energy models but this paper should be seen as a review on the phenomena
responsible for the acceleration.
Moreover, in a landscape of hardly compelling theories, it is an important
task to build simple measurable parameters useful for future experiments that
will help us to understand more about the evolution of the Universe.
Using Chandra X-ray and VLA radio data, we investigate the scaling relationship between jet power, P_jet, and synchrotron luminosity, P_rad. We expand the sample presented in Birzan et al. (2008) to lower radio power by incorporating measurements for 21 gEs to determine if the Birzan et al. (2008) P_jet-P_rad scaling relations are continuous in form and scatter from giant elliptical galaxies (gEs) up to brightest cluster galaxies (BCGs). We find a mean scaling relation of P_jet approximately 5.8x10^43 (P_rad/10^40)^(0.70) erg/s which is continuous over ~6-8 decades in P_jet and P_rad with a scatter of approximately 0.7 dex. Our mean scaling relationship is consistent with the model presented in Willott et al. (1999) if the typical fraction of lobe energy in non-radiating particles to that in relativistic electrons is > 100. We identify several gEs whose radio luminosities are unusually large for their jet powers and have radio sources which extend well beyond the densest parts of their X-ray halos. We suggest that these radio sources are unusually luminous because they were unable to entrain appreciable amounts of gas.
We consider gravitino couplings in theories with broken gauge symmetries. In particular, we compute the single gravitino production cross section in W+ W- fusion processes. Despite recent claims to the contrary, we show that this process is always subdominant to gluon fusion processes in the high energy limit. The full calculation is performed numerically; however, we give analytic expressions for the cross section in the supersymmetric and electroweak limits. We also confirm these results with the use of the effective theory of goldstino interactions.
We consider the parameterised post-Newtonian limit of a general class of bimetric theories of gravity, in which both metrics are dynamical. It is found that these theories can evade solar system tests of post-Newtonian gravity remarkably well. We show that the perturbations about Minkowski space in these theories contain both massless and massive degrees of freedom, and that in general there are two different types of massive mode, each with a different mass. If both of these masses are sufficiently large then the predictions of the most general class of theories we consider are indistinguishable from those of general relativity, up to post-Newtonian order in a weak field, low velocity expansion. In the limit that the massive modes become massless, we find that these general theories do not exhibit a van Dam-Veltmam-Zakharov-like discontinuity in their gamma parameter, although there are discontinuities in other post-Newtonian parameters as the massless limit is approached. This smooth behaviour in gamma is due to the discontinuities from each of the two different massive modes cancelling each other out. Such cancellations cannot occur in special cases with only one mass parameter, such as the Isham-Salam-Strathdee theory.
We computed a comprehensive set of theoretical ultraviolet spectra of hot, massive stars with the radiation-hydrodynamics code WM-Basic. This model atmosphere and spectral synthesis code is optimized for computing the strong P Cygni-type lines originating in the winds of hot stars, which are the strongest features in the ultraviolet spectral region. The computed set is suitable as a spectral library for inclusion in evolutionary synthesis models of star clusters and star-forming galaxies. The chosen stellar parameters cover the upper left Hertzsprung-Russell diagram at L >~ 10^2.75 Lsun and T_eff >~ 20,000 K. The adopted elemental abundances are 0.05 Zsun, 0.2 Zsun, 0.4 Zsun, Zsun, and 2 Zsun. The spectra cover the wavelength range from 900 to 3000 {\AA} and have a resolution of 0.4 {\AA}. We compared the theoretical spectra to data of individual hot stars in the Galaxy and the Magellanic Clouds obtained with the International Ultraviolet Explorer (IUE) and Far Ultraviolet Spectroscopic Explorer (FUSE) satellites and found very good agreement. We built a library with the set of spectra and implemented it into the evolutionary synthesis code Starburst99 where it complements and extends the existing empirical library towards lower chemical abundances. Comparison of population synthesis models at solar and near-solar composition demonstrates consistency between synthetic spectra generated with either library. We discuss the potential of the new library for the interpretation of the rest-frame ultraviolet spectra of star-forming galaxies. Properties that can be addressed with the models include ages, initial mass function, and heavy-element abundance. The library can be obtained both individually or as part of the Starburst99 package.
Particle theorists typically use expectation values to study the quantum back-reaction on inflation, whereas many cosmologists stress the stochastic nature of the process. While expectation values certainly give misleading results for some things, such as the stress tensor, we argue that operators exist for which there is no essential problem. We quantify this by examining the stochastic properties of a noninteracting, massless, minimally coupled scalar on a locally de Sitter background. The square of the stochastic realization of this field seems to provide an example of great relevance for which expectation values are not misleading. We also examine the frequently expressed concern that significant back-reaction from expectation values necessarily implies large stochastic fluctuations between nearby spatial points. Rather than viewing the stochastic formalism in opposition to expectation values, we argue that it provides a marvelously simple way of capturing the leading infrared logarithm corrections to the latter, as advocated by Starobinsky.
The acceleration of cosmic rays is conjectured to be the output from various interactions with the electromagnetic fields in astrophysical bodies, like magnetic matter clumps, and from the well-known shock and stochastic Fermi mechanism. The latter apparently does not depend on the particle's charge, quantitatively. Therefore, the motion of the charged particle parallel to magnetic field $\mathbf{B}$ and under the influence of the force $\mathbf{F}$. is assumed to be composed in an acceleration by non-magnetic force $\mathbf{F}_{\parallel}$ and gyromotion along $\mathbf{B}$, plus a drift in direction of $\mathbf{F}_{\perp}$. In this letter, the model and its formalism are introduced. Also various examples for drift and accelerating forces are studied.
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We use a complete sample of Lya emission-line selected AGNs obtained from nine deep blank fields observed with the grism spectrographs on the Galaxy Evolution Explorer (GALEX) satellite to measure the normalization and spectral shape of the AGN contribution to the ionizing background (rest-frame wavelengths 700-900 A) at z~1. Our sample consists of 139 sources selected in the redshift range z=0.65-1.25 in the near-ultraviolet (NUV; 2371 A central wavelength) channel. The area covered is 8.2 square degrees to a NUV magnitude of 20.5 (AB) and 0.92 square degrees at the faintest magnitude limit of 21.8. The GALEX AGN luminosity function agrees well with those obtained using optical and X-ray AGN samples, and the measured redshift evolution of the ionizing volume emissivity is similar to that previously obtained by measuring the GALEX far-ultraviolet (FUV; 1528 A central wavelength) magnitudes of an X-ray selected sample. For the first time we are able to construct the shape of the ionizing background at z~1 in a fully self-consistent way.
We discuss the formation of dark matter caustics, and their possible detection by future dark matter experiments. The annual modulation expected in the recoil rate measured by a dark matter detector is discussed. We consider the example of dark matter particles with a Maxwell-Boltzmann velocity distribution modified by a cold stream due to a nearby caustic. It is shown that the effect of the caustic flow is potentially detectable, even when the density enhancement due to the caustic is small. This makes the annual modulation effect an excellent probe of inner caustics. We also show that the phase of the annual modulation at low recoil energies does not constrain the particle mass unless the velocity distribution of particles in the solar neighborhood in known.
AGN feedback is believed to play an important role in shaping a variety of observed galaxy properties, as well as the evolution of their stellar masses and star formation rates. In particular, in the current theoretical paradigm of galaxy formation, AGN feedback is believed to play a crucial role in regulating the levels of activity in galaxies, in relatively massive halos at low redshift. Only in recent years, however, detailed statistical information on the dependence of galaxy activity on stellar mass, parent halo mass and hierarchy has become available. In this paper, we compare the fractions of galaxies belonging to different activity classes (star-forming, AGN and radio active) with predictions from four different and independently developed semi-analytical models. We adopt empirical relations to convert physical properties into observables (H_alpha emission lines, OIII line strength and radio power). We demonstrate that all models used in this study reproduce the overall distributions of galaxies belonging to different activity classes as a function of stellar mass and halo mass: star forming galaxies and the strongest radio sources are preferentially associated with low-mass and high-mass galaxies/halos respectively. However, model predictions differ from observational measurements in a number of ways. All models used in our study predict that almost every >1.e12 Msun dark matter halo and/or >1.e11 Msun galaxy should host a bright radio source, while only a small fraction of galaxies belong to this class in the data. In addition, radio brightness is expected to depend strongly on the mass of the parent halo mass in the models, while strong and weak radio galaxies are found in similar environments in data. Our results highlight that the distribution of AGN as a function of stellar mass provides one of the most promising discriminants between different gas accretion schemes.
Here, we model the effect of non-uniform dynamical mass distributions and their associated gravitational fields on the stationary galactic superwind solution. We do this by considering an analogue injection of mass and energy from stellar winds and SNe. We give analytical formulae that establish when an outflow is possible and also characterize distinct flow regimes and enrichment scenarios. We also constraint the parameter space by giving approximate limits above which gravitation, self-gravitation and radiative cooling can inhibit the stationary flow. Later, we obtain analytical expressions for the free superwind hydrodynamical profiles. We find that the existence or inhibition of the superwind solution highly depends on the steepness and concentration of the dynamical mass and the mass and energy injection rates, not just in their effective total values. We compare our results with observational data and a recent numerical work that models artificial massive galaxies assuming a uniform distribution of their parameters. Finally, we put our results in the context of the mass-metallicity relationship to discuss observational evidence related to the selective loss of metals from the less massive galaxies and the recent discovery of high-metallicity dwarf spheroidal (dSph) and dwarf elliptical (dE) galaxies.
We consider a scale invariant model which includes a $R^{2}$ term in action and show that a stable "emerging universe" scenario is possible. The model belongs to the general class of theories, where an integration measure independent of the metric is introduced. To implement scale invariance (S.I.), a dilaton field is introduced. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking (S.S.B) of S.I. After S.S.B. of S.I. in the model with the $R^{2}$ term (and first order formalism applied), it is found that a non trivial potential for the dilaton is generated. The dynamics of the scalar field becomes non linear and these non linearities are instrumental in the stability of some of the emerging universe solutions, which exists for a parameter range of the theory.
In this second part, we generalize the results of the previous paper. We present an analytic superwind solution considering extended gravitationally-interacting dark-matter and baryonic haloes. The incorporation of the latter is critical, since they can have a substantial effect on the hydrodynamics of superwinds generated by massive galaxies. Although the presence of extended and massive haloes does not change the limit for the closed-box enrichment of galaxies established in the first paper, they can trigger an earlier activation of the open-box enrichment scenario, since their gravitational potentials can contribute to the inhibition of the free superwind. Moreover, the incorporation of the extended haloes will also enhance the physical setting behind the superwind model, as we consider mass distributions with properties that emulate the results of recent simulations of $\Lambda$CDM haloes.
Type Ia supernovae (SNIa) remain mysterious despite their central importance in cosmology and their rapidly increasing discovery rate. The progenitors of SNIa can be probed by the delay time between stellar birth and death. The explosions and progenitors of SNIa can be probed by MeV nuclear gamma rays emitted in the decays of radioactive nickel and cobalt into iron. We compare the cosmic star formation and SNIa rates, finding that their different redshift evolution requires a large fraction of SNIa to have large delay times. A delay time distribution of the form t^{-1.0+/-0.3} provides a good fit, implying 50% of SNIa explode more than ~ 1 Gyr after progenitor birth. The extrapolation of the cosmic SNIa rate to z = 0 agrees with the rate we deduce from catalogs of local SNIa. We investigate prospects for gamma-ray telescopes to exploit the facts that escaping gamma rays directly reveal the power source of SNIa and uniquely provide tomography of the expanding ejecta. We find large improvements relative to earlier studies by Gehrels et al. (1987) and Timmes & Woosley (1997) due to larger and more certain SNIa rates and advances in gamma-ray detectors. The proposed Advanced Compton Telescope, with a narrow-line sensitivity ~ 60 times better than that of current satellites, would, on an annual basis, detect up to ~ 100 SNIa (3 sigma) and provide revolutionary model discrimination for SNIa within 20 Mpc, with gamma-ray light curves measured with ~ 10 sigma significance daily for ~ 100 days. Even more modest improvements in detector sensitivity would open a new and invaluable astronomy with frequent SNIa gamma-ray detections.
It has been suggested by Chen and Lai that the proper description of the large scale structure formation of the universe in the post-reionization era, which is conventionally characterized via gas hydrodynamics, should include the plasma collective effects in the formulation. Specifically, it is the combined pressure from the baryon thermal motions and the residual long-range electrostatic potentials resulted from the imperfect Debye shielding, that fights against the gravitational collapse. As a result, at small-scales the baryons would oscillate at the ion-acoustic, instead of the conventional neutral acoustic, frequency. In this paper we extend and improve the Chen-Lai formulation with the attention to the Landau damping of the ion-acoustic oscillations. Since T_e \sim T_i in the post-reionization era, the ion acoustic oscillations would inevitably suffer the Landau damping which severely suppresses the baryon density spectrum in the regimes of intermediate and high wavenumber k. To describe this Landau-damping phenomenon more appropriately, we find it necessary to modify the filtering wavenumber k_f in our analysis. It would be interesting if our predicted Landau damping of the ion-acoustic oscillations can be observed at high redshifts.
We address the issue of setting up generic non-Gaussian initial conditions for N-body simulations. We consider inflationary-motivated primordial non-Gaussianity where the perturbations in the Bardeen potential are given by a dominant Gaussian part plus a non-Gaussian part specified by its bispectrum. The approach we explore here is suitable for any bispectrum, i.e. it does not have to be of the so-called separable or factorizable form. The procedure of generating a non-Gaussian field with a given bispectrum (and a given power spectrum for the Gaussian component) is not univocal, and care must be taken so that higher-order corrections do not leave a too large signature on the power spectrum. This is so far a limiting factor of our approach. We then run N-body simulations for the most popular inflationary-motivated non-Gaussian shapes. The halo mass function and the non-linear power spectrum agree with theoretical analytical approximations proposed in the literature, even if they were so far developed and tested only for a particular shape (the local one). We plan to make the simulations outputs available to the community via the non-Gaussian simulations comparison project web site this http URL
Type Ia Supernovae (SNe Ia) form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates. This one-parameter behavior allows SNe Ia to be calibrated as cosmological `standard candles', and led to the discovery of an accelerating Universe. Recent investigations, however, have revealed that the true nature of SNe Ia is more complicated. Theoretically, it has been suggested that the initial thermonuclear sparks are ignited at an offset from the centre of the white-dwarf (WD) progenitor, possibly as a result of convection before the explosion. Observationally, the diversity seen in the spectral evolution of SNe Ia beyond the luminosity decline-rate relation is an unresolved issue. Here we report that the spectral diversity is a consequence of random directions from which an asymmetric explosion is viewed. Our findings suggest that the spectral evolution diversity is no longer a concern in using SNe Ia as cosmological standard candles. Furthermore, this indicates that ignition at an offset from the centre of is a generic feature of SNe Ia.
We present two methods that enable us to obtain approximate solutions of the lens equation near the fold caustic with an arbitrary degree of accuracy. We obtain "post-linear" corrections to the well known linear caustic approximation formula for the total amplification of two critical images of a point source. In order to obtain the non-trivial corrections we had to take into account the Taylor expansion of the lens equation near caustic up to the fourth order. The result is used to obtain amplification of the extended Gaussian source in this "post-linear" order; the amplification is reduced to the form containing three additional fitting parameters. The conditions of neglecting the correction terms are analyzed. The modified amplification formula is applied to the fitting of light curves of the Q2237+0305 gravitational lens system in the vicinity of high amplification events (HAE). We show that introduction of some of the "post-linear" corrections reduces \c{hi}2 by 30 per cent in case of known HAE on the light curve of the image C (1999). These corrections may be important for a precise comparison of different source models on account of observational data.
Measurements of the 2.7 K cosmic microwave background (CMB) radiation now provide the most stringent constraints on cosmological models. The power spectra of the temperature anisotropies and the $E$-mode polarization of the CMB are explained well by the inflationary paradigm. The next generation of CMB experiments aim at providing the most direct evidence for inflation through the detection of $B$-modes in the CMB polarization, presumed to have been caused by gravitational waves generated during the inflationary epoch around $10^{-34}$s. The $B$-mode polarization signals are very small ($\leq$10$^{-8}$K) compared with the temperature anisotropies ($\sim 10^{-4}$K). Systematic effects in CMB telescopes can cause leakage from temperature anisotropy into polarization. Bolometric interferometry (BI) is a novel approach to measuring this small signal with lower leakage. If BI can be made to work over wide bandwidth ($\sim20-30\%$) it can provide similar sensitivity to imagers. Subdividing the frequency passband of a Fizeau interferometer would mitigate the problem of `fringe smearing.' Furthermore, the approach should allow simultaneous measurements in image space and visibility space. For subdividing the frequency passsband (`sub-band splitting' henceforth), we write an expression for the output from every baseline at every detector in the focal plane as a sum of visibilities in different frequency sub-bands. For operating the interferometer simultaneously as an imager, we write the output as two integrals over the sky and the focal plane, with all the phase differences accounted for.}{The sub-band splitting method described here is general and can be applied to broad-band Fizeau interferometers across the electromagnetic spectrum. Applications to CMB measurements and to long-baseline optical interferometry are promising.
Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Bootes 1, and Willman 1 conducted by VERITAS. These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical background of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of ~20 hours. The 95% confidence upper limits on the integral gamma-ray flux are in the range 0.4-2.2x10^-12 photons cm^-2s^-1. We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs. The limits are obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and are approximately three orders of magnitude above the generic theoretical prediction for WIMPs in the minimal supersymmetric standard model framework. However significant uncertainty exists in the dark matter distribution as well as the neutralino cross sections which under favorable assumptions could further lower the limits.
We present gamma-ray observations with the LAT on board the Fermi Gamma-Ray Telescope of the nearby radio galaxy Centaurus~A. The previous EGRET detection is confirmed, and the localization is improved using data from the first 10 months of Fermi science operation. In previous work, we presented the detection of the lobes by the LAT; in this work, we concentrate on the gamma-ray core of Cen~A. Flux levels as seen by the LAT are not significantly different from that found by EGRET, nor is the extremely soft LAT spectrum ($\G=2.67\pm0.10_{stat}\pm0.08_{sys}$ where the photon flux is $\Phi\propto E^{-\G}$). The LAT core spectrum, extrapolated to higher energies, is marginally consistent with the non-simultaneous HESS spectrum of the source. The LAT observations are complemented by simultaneous observations from Suzaku, the Swift Burst Alert Telescope and X-ray Telescope, and radio observations with the Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TANAMI) program, along with a variety of non-simultaneous archival data from a variety of instruments and wavelengths to produce a spectral energy distribution (SED). We fit this broadband data set with a single-zone synchrotron/synchrotron self-Compton model, which describes the radio through GeV emission well, but fails to account for the non-simultaneous higher energy TeV emission observed by HESS from 2004-2008. The fit requires a low Doppler factor, in contrast to BL Lacs which generally require larger values to fit their broadband SEDs. This indicates the $\g$-ray emission originates from a slower region than that from BL Lacs, consistent with previous modeling results from Cen~A. This slower region could be a slower moving layer around a fast spine, or a slower region farther out from the black hole in a decelerating flow.
We present a study of a large, statistically complete sample of star-forming dwarf galaxies using mid-infrared observations from the {\it Spitzer Space Telescope}. The relationships between metallicity, star formation rate (SFR) and mid-infrared color in these systems show that the galaxies span a wide range of properties. However, the galaxies do show a deficit of 8.0 \um\ polycyclic aromatic hydrocarbon emission as is apparent from the median 8.0 \um\ luminosity which is only 0.004 \lstarf\ while the median $B$-band luminosity is 0.05 \lstarb. Despite many of the galaxies being 8.0 \um\ deficient, there is about a factor of 4 more extremely red galaxies in the [3.6] $-$ [8.0] color than for a sample of normal galaxies with similar optical colors. We show correlations between the [3.6] $-$ [8.0] color and luminosity, metallicity, and to a lesser extent SFRs that were not evident in the original, smaller sample studied previously. The luminosity--metallicity relation has a flatter slope for dwarf galaxies as has been indicated by previous work. We also show a relationship between the 8.0 \um\ luminosity and the metallicity of the galaxy which is not expected given the competing effects (stellar mass, stellar population age, and the hardness of the radiation field) that influence the 8.0 \um\ emission. This larger sample plus a well-defined selection function also allows us to compute the 8.0 \um\ luminosity function and compare it with the one for the local galaxy population. Our results show that below 10$^{9}$ $L$\solar, nearly all the 8.0 \um\ luminosity density of the local universe arises from dwarf galaxies that exhibit strong \ha\ emission -- i.e., 8.0 \um\ and \ha\ selection identify similar galaxy populations despite the deficit of 8.0 \um\ emission observed in these dwarfs.
We investigate the role of thermal fluctuations and of the finite number of monomers in small clusters of carbon atoms on the nucleation rate of carbonaceous grains. Thermal fluctuations are due to the quantized nature of the energy exchanges between the clusters, the gas, and the radiation field. Nanoscale effects modify the spontaneous detachment of monomers due to the finite amount of internal energy contained in small clusters. We find that both corrections have a big impact on the stability of the clusters and on the rate of nucleation. We implement our model within a Monte Carlo code to derive the new stability conditions for clusters as well as nucleation rates. Due to computing limitations, we can explore the consequences of this approach only at high temperatures, at which particle interactions are not much less frequent than photon interactions. We found that the combined effect of the detachment correction and the temperature fluctuations produces faster nucleation. We also found that the nucleation rate depends on the composition of the gas and not only on the partial pressure of the compound that condensates into grains. This is a unique result of this model that can be used to prove or disprove it.
We consider metric f(R) theories of gravity without mapping them to their scalar-tensor counterpart, but using the Ricci scalar itself as an "extra" degree of freedom. This approach avoids then the introduction of a scalar-field potential that might be ill defined (not single valued). In order to explicitly show the usefulness of this method we focus on static and spherically symmetric spacetimes and deal with the recent controversy about the existence of extended relativistic objects in certain class of f(R) models.
We have mapped the northern area (30' x20') of a local group spiral galaxy M33 in 12CO(J=1-0) emission line with the 45m telescope at Nobeyama Radio Observatory (NRO). Along with the Halpha and Spitzer 24 micron data, we have investigated the relationship between the surface density of molecular gas mass and the star formation rate (SFR) in an external galaxy (Kennicutt-Schmidt law) with the highest spatial resolution (~80 pc) to date. This resolution is comparable to the scale of giant molecular clouds (GMCs). At the positions where CO is detected, the SFR surface density exhibits a very wide range of up to four orders of magnitude, from Sigma(SFR)< ~10^{-10} to ~10^{-6}M_solar yr^{-1}pc^{-2}, whereas the Sigma(H2) values are mostly in the range of 10-40 M_solar pc^{-2}. It is found that the gas surface density and SFR correlate well at a resolution of ~1 kpc, but it becomes looser with higher resolution and breaks down at GMC scales. The scatter of the Sigma(SFR)-Sigma(H2) relationship in the ~80 pc resolution results from the variety of star forming activity among GMCs. Their variety is attributed to the drift of young clusters from their parent GMCs and to the variety in the evolutionary stages of GMCs. This result shows that the Kennicutt-Schmidt law is valid only in scales larger than that of GMCs, when we average the spatial offset between GMCs and the star forming regions, and their various evolutionary stages.
We present a model of the gravitational field based on two symmetric tensors. Outside matter, the predictions of the model coincide exactly with General Relativity, so all classical tests are satisfied. In Cosmology, we get accelerated expansion without a cosmological constant.
Thanks to the wide field of view of its gamma-ray imager, the AGILE satellite obtained a long term monitoring of the brightest blazars in the sky and during the first 3 years of operation detected several blazars in a high gamma-ray state: 3C 279, 3C 454.3, PKS 1510-089, S5 0716+714, 3C 273, W Comae, and Mrk 421. Through the rapid dissemination of our alerts we were able to obtain also multi-wavelength data from many observatories such as Spitzer, Swift, RXTE, Suzaku, XMM-Newton, INTEGRAL, MAGIC, VERITAS, and ARGO as well as radio-to-optical coverage by means of the MOJAVE project, the GASP project of the WEBT and the REM Telescope. This large coverage over the whole electromagnetic spectrum gave us the opportunity to study the variability correlations between the emission at different frequencies and to build truly simultaneous spectral energy distributions of these sources from radio to gamma-rays, investigating in detail the emission mechanisms of blazars and uncovering in some cases a more complex behaviour with respect to the standard models. We present an overview of the most interesting AGILE results on these gamma-ray blazars and the relative multiwavelength data.
We examine the necessary physical underpinnings for setting up the cosmological standard model with a global cosmic time parameter. In particular, we discuss the role of Weyl's principle which asserts that cosmic matter moves according to certain regularity requirements. After a brief historical introduction to Weyl's principle we argue that although the principle is often not explicitly mentioned in modern standard texts on cosmology, it is implicitly assumed and is, in fact, necessary for a physically well-defined notion of cosmic time. We finally point out that Weyl's principle might be in conflict with the wide-spread idea that the universe at some very early stage can be described exclusively in terms of quantum theory.
We investigate effects of a special kind of dynamical deformation between momenta of the existing field of the Brans-Dicke theory and scale factor of the FRW metric. This choice linearly includes a deformation parameter. Then, we trace its footprints in cosmological equations of motion when the BD coupling parameter goes to infinity. One result gives a constant scale factor in the late time, as obtained before in the literature, which can be interpreted as a quantum gravity footprint in the large scale. Another result regularizes the big bang singularity, and its accelerating expansion region has an infinite temporal range which overcomes the horizon problem. Then, after this epoch, there is a graceful exiting by which the universe enters in the radiation dominated era.
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Before the universe was reionized, it was likely that the spin temperature of intergalactic hydrogen was decoupled from the CMB by UV radiation from the first stars through the Wouthuysen-Field effect. If the IGM had not yet been heated above the CMB temperature by that time, then the gas would appear in absorption relative to the CMB. Large, rare sources of X-rays could inject sufficient heat into the neutral IGM, so that the differential brightness temperature was greater than zero at comoving distances of tens to hundreds of Mpc, resulting in large 21-cm fluctuations with amplitudes of about 250 mK on arcminute to degree angular scales, an order of magnitude larger in amplitude than that caused by ionized bubbles during reionization, about 25 mK. This signal could therefore be easier to detect and probe higher redshifts than that due to patchy reionization. For the case in which the first objects to heat the IGM are QSOs hosting 10^7-solar mass black holes with an abundance exceeding about 1 per Gpc^3 at z~15, observations with either the Arecibo Observatory or the Five Hundred Meter Aperture Spherical Telescope (FAST) could detect and image their fluctuations at greater than 5-sigma significance in about a month of dedicated survey time. Additionally, existing facilities such as MWA and LOFAR could detect the statistical fluctuations arising from a population of 10^5-solar mass black holes with an abundance of about 10^4 per Gpc^3 at z~10-12.
We present a high resolution (FWHM=2.7 km/s), high S/N echelle spectrum for the z = 2.26 QSO J2123-0050 and determine elemental abundances for the z = 2.06 sub-DLA in its line of sight. This high redshift sub-DLA has a complex kinematic structure and harbours detections of neutral (SI, CI), singly (e.g. CII, SII) and multiply ionized (e.g. CIV, SiIV) species as well as molecular H and HD. The plethora of detected transitions in various ionization stages is indicative of a complex multi-phase structure present in this high redshift galaxy. We demonstrate that the ionization corrections in this sub-DLA are significant (up to ~0.7 dex). For example, if no ionization correction is applied, a super-solar metallicity is derived ([S/H] = +0.36), whereas a single phase ionization correction reduces this to [S/H] = -0.19. The theoretical impact of a multi-phase medium is investigated through Cloudy modelling and it is found that the abundances of Si, S and Fe are always over-estimated (by up to 0.15 dex in our experiments) if a single-phase is assumed. Therefore, although Cloudy models improve estimates of metal column densities, the simplification of a single phase medium leaves a systematic error in the result, so that even ionization-corrected abundances may still be too high. Without ionization corrections the properties of this sub-DLA appear to require extreme scenarios of nucleosynthetic origins. After ionization corrections are applied the ISM of this galaxy appears to be similar to some of the sightlines through the Milky Way.
Using an analytical model, we study the evolution of subhalo, including its mass, angular momentum and merging time-scale. This model considers the dominant processes governing subhalo evolution, such as dynamical friction, tidal stripping and tidal heating. We find that in order to best match the evolution of angular momentum measured from N-body simulation, mass stripping by tidal force should become inefficient after subhalo has experienced a few passages of pericenter. It is also found that the often used Coulomb logarithm $\ln M/m$ has to be revised to best fit the merging time-scales from simulation. Combining the analytical model with the Extended Press-Schechter (EPS) based merger trees, we study the subhalo mass function, and their spatial distribution in a Milky-Way (MW) type halo. By tuning the tidal stripping efficiency, we can gain a better match to the subhalo mass function from simulation. The predicted distribution of subhaloes is found to agree with the distribution of MW satellites, but is more concentrated than the simulation results. The radial distribution of subhaloes depends weakly on subhaloes mass at both present day and the time of accretion, but strongly on the accretion time. Using the improved model, we measure the second moment of the subhalo occupation distribution, and it agrees well with the results of Kravtsov et al. (2004a) and Zheng et al. (2005).
Burrage, Davis, and Shaw recently suggested exploiting the correlations between high and low energy luminosities of astrophysical objects to probe possible mixing between photons and axion-like particles (ALP) in magnetic field regions. They also presented evidence for the existence of ALP's by analyzing the optical/UV and X-ray monochromatic luminosities of AGNs. We extend their work by using the monochromatic luminosities of 320 unobscured Active Galactic Nuclei from the Sloan Digital Sky Survey/Xmm-Newton Quasar Survey (Young et al., 2009), which allows the exploration of 18 different combinations of optical/UV and X-ray monochromatic luminosities. However, we do not find compelling evidence for the existence of ALPs. Moreover, it appears that the signal reported by Burrage et al. is more likely due to X-ray absorption rather than to photon-ALP oscillation.
We report spectropolarimetry of 30 radio-selected broad absorption line (BAL) quasars with the Keck Observatory, 25 from the sample of Becker et al. (2000). Both high and low-ionization BAL quasars are represented, with redshifts ranging from 0.5 to 2.5. The spectropolarimetric properties of radio-selected BAL quasars are very similar to those of radio-quiet BAL quasars: a sizeable fraction (20%) show large continuum polarization (2-10%) usually rising toward short wavelengths, emission lines are typically less polarized than the continuum, and absorption line troughs often show large polarization jumps. There are no significant correlations between polarization properties and radio properties, including those indicative of system orientation, suggesting that BAL quasars are not simply normal quasars seen from an edge-on perspective.
We report two detections of deuterated molecular hydrogen (HD) in QSO absorption-line systems at $z > 2$. Toward J2123-0500, we find $N$(HD) $= 13.84 \pm 0.2$ for a sub-DLA with metallicity $\simeq 0.5Z_{\odot}$ and $N$(H$_2$) = $17.64 \pm 0.15$ at $z = 2.0594$. Toward FJ0812+32, we find $N$(HD) $= 15.38 \pm 0.3$ for a solar-metallicity DLA with $N$(H$_2$) = $19.88 \pm 0.2$ at $z = 2.6265$. These systems have ratios of HD to H$_2$ above that observed in dense clouds within the Milky Way disk and apparently consistent with a simple conversion from the cosmological ratio of D/H. These ratios are not readily explained by any available model of HD chemistry and there are no obvious trends with metallicity or molecular content. Taken together, these two systems and the two published $z > 2$ HD-bearing DLAs indicate that HD is either less effectively dissociated or more efficiently produced in high-redshift interstellar gas, even at low molecular fraction and/or solar metallicity. It is puzzling that such diverse systems should show such consistent HD/H$_2$ ratios. Without clear knowledge of all the aspects of HD chemistry that may help determine the ratio HD/H$_2$, we conclude that these systems are potentially more revealing of gas chemistry than of D/H itself and that it is premature to use such systems to constrain D/H at high-redshift.
We have imaged an 11.5 sq. deg. region of sky towards the South Ecliptic Pole (RA = 04h43m, Dec = -53d40m, J2000) at 24 and 70 microns with MIPS, the Multiband Imaging Photometer for Spitzer. This region is coincident with a field mapped at longer wavelengths by the Balloon-borne Large Aperture Submillimeter Telescope. We discuss our data reduction and source extraction procedures. The median depths of the maps are 47 microJy/beam at 24 micron and 4.3 mJy/beam at 70 micron. At 24 micron, we identify 93098 point sources with signal-to-noise ratio (SNR) >5, and an additional 63 resolved galaxies; at 70 micron, we identify 891 point sources with SNR >6. From simulations, we determine a false detection rate of 1.8% (1.1%) for the 24 micron (70 micron) catalog. The 24 and 70 micron point-source catalogs are 80% complete at 230 microJy and 11 mJy, respectively. These mosaic images and source catalogs will be available to the public through the NASA/IPAC Infrared Science Archive.
This paper studies the stability of warm inflationary solutions when the viscous pressure is taken into account. The latter is a very natural and physically motivated ingredient of warm inflation and is seen to widen the stability range of warm inflation. The spectral index parameters, $n_{s}$, $n_{T}$, and their ratio are derived. The corresponding WMAP7 data are used to fix some parameters of the model. Two specific examples are discussed in detail: (i) a potential given by $V(\phi, T) = v_{1}(\phi)\, + \, v_{2}(T)$, and (ii) a potential of the form $V(\phi, T) = \alpha \, v_{1}(\phi) \, v_{2}(T)$. In both cases, the viscosity has little impact on the said ratio.
Using the Spitzer Space Telescope, we have obtained rest frame 9-16mu spectra of 11 quasars and 9 radio galaxies from the 3CRR catalog at redshifts 1.0<z<1.4. This complete flux-limited 178MHz-selected sample is unbiased with respect to orientation and therefore suited to study orientation-dependent effects in the most powerful active galactic nuclei (AGN). The mean radio galaxy spectrum shows a clear silicate absorption feature (tau_9.7mu = 1.1) whereas the mean quasar spectrum shows silicates in emission. The mean radio galaxy spectrum matches a dust-absorbed mean quasar spectrum in both shape and overall flux level. The data for individual objects conform to these results. The trend of the silicate depth to increase with decreasing core fraction of the radio source further supports that for this sample, orientation is the main driver for the difference between radio galaxies and quasars, as predicted by AGN unification. However, comparing our high-z sample with lower redshift 3CRR objects reveals that the absorption of the high-z radio galaxy MIR continuum is lower than expected from a scaled up version of lower luminosity sources, and we discuss some effects that may explain these trends.
We investigate the global dynamic stability of spherical clouds in the Broad Line Region (BLR) of Active Galactic Nuclei (AGN), exposed to radial radiation pressure, gravity of the central black hole (BH), and centrifugal forces assuming the clouds adapt their size according to the local pressure. We consider both, isotropic and anisotropic light sources. In both cases, stable orbits exist also for very sub-Keplerian rotation for which the radiation pressure contributes substantially to the force budget. We demonstrate that highly excentric, very sub-Keplerian stable orbits may be found that also agree with the recent finding by spectropolarimetry that the BLR is disk-like. This gives further support for the model of Marconi et al. 2008, which is designed to improve the agreement between black hole masses derived in certain active galaxies based on BLR dynamics, and black hole masses derived by other means in other galaxies by inclusion of a luminosity dependent term. For anisotropic illumination, the foreshortening of orbits in the direction of maximum radiative force naturally leads to a disk-like geometry for cloud systems with comparatively low column densities.
We present high-resolution interferometric Submillimeter Array (SMA) imaging at 890 microns (~2" resolution) of two millimeter selected galaxies -- MMJ100015+021549 and MMJ100047+021021 -- discovered with the Max-Planck Millimeter Bolometer (MAMBO) on the IRAM 30 m telescope and also detected with Bolocam on the CSO, in the COSMOS field. The first source is significantly detected at the ~11 sigma level, while the second source is tentatively detected at the ~4 sigma level, leading to a positional accuracy of ~0.2-0.3". MM100015+021549 is identified with a faint radio and K-band source. MMJ100047+021021 shows no radio emission and is tentatively identified with a very faint K-band peak which lies at ~1.2" from a clumpy optical source. The submillimeter-to-radio flux ratio for MM100015+021549 yields a redshift of ~4.8, consistent with the redshift implied by the UV-to-submillimeter photometry, z~3.0-5.0. We find evidence for warm dust in this source with an infrared luminosity in the range ~0.9-2.5x10^{13} L_sun, supporting the increasing evidence for a population luminous submillimeter galaxies at z>3. Finally, the lack of photometric data for MMJ100047+021021 does not allow us to investigate its properties in detail, however its submillimeter-to-radio ratio implies z>3.5.
The anomaly in the Cosmic Microwave Background known as the "Cold Spot" could be due to the existence of an anomalously large spherical (few hundreds Mpc/h radius) underdense region, called a "Void" for short. Such a structure would have an impact on the CMB also at high multipoles l through Lensing. This would then represent a unique signature of a Void. Modeling such an underdensity with an LTB metric, we show that the Lensing effect leads to a large signal in the non-diagonal two-point function, centered in the direction of the Cold Spot, such that the Planck satellite will be able to confirm or rule out the Void explanation for the Cold Spot, for any Void radius with a Signal-to-Noise ratio of at least O(10).
We place functional constraints on the shape of the inflaton potential from the cosmic microwave background through a variant of the generalized slow roll approximation that allows large amplitude, rapidly changing deviations from scale-free conditions. Employing a principal component decomposition of the source function G'~3(V'/V)^2 - 2V''/V and keeping only those measured to better than 10% results in 5 nearly independent Gaussian constraints that maybe used to test any single-field inflationary model where such deviations are expected. The first component implies < 3% variations at the 100 Mpc scale. One component shows a 95% CL preference for deviations around the 300 Mpc scale at the ~10% level but the global significance is reduced considering the 5 components examined. This deviation also requires a change in the cold dark matter density which in a flat LCDM model is disfavored by current supernova and Hubble constant data and can be tested with future polarization or high multipole temperature data. Its impact resembles a local running of the tilt from multipoles 30-800 but is only marginally consistent with a constant running beyond this range. For this analysis, we have implemented a ~40x faster WMAP7 likelihood method which we have made publicly available.
A rich variety of order parameter manifolds of multicomponent Bose-Einstein condensates (BECs) admit various kinds of topological excitations, such as fractional vortices, monopoles, skyrmions, and knots. In this paper, we discuss two topological excitations in spinor BECs: non-Abelian vortices and knots. Unlike conventional vortices, non-Abelian vortices neither reconnect themselves nor pass through each other, but create a rung between them in a topologically stable manner. We discuss the collision dynamics of non-Abelian vortices in the cyclic phase of a spin-2 BEC. In the latter part, we show that a knot, which is a unique topological object characterized by a linking number or a Hopf invariant [$\pi_3 (S^2)=Z$], can be created using a conventional quadrupole magnetic field in a cold atomic system.
We propose a novel cosmological scenario, in which standard inflation is replaced by an expanding phase with a drastic violation of the Null Energy Condition (NEC): \dot H >> H^2. The model is based on the recently introduced Galileon theories, that allow NEC violating solutions without instabilities. The unperturbed solution describes a Universe that is asymptotically Minkowski in the past, expands with increasing energy density until it exits the regime of validity of the effective field theory and reheats. This solution is a dynamical attractor and the Universe is driven to it, even if it is initially contracting. The study of perturbations of the Galileon field reveals some subtleties, related to the gross violation of the NEC and it shows that adiabatic perturbations are cosmologically irrelevant. The model, however, suggests a new way to produce a scale invariant spectrum of isocurvature perturbations, which can later be converted to adiabatic: the Galileon is forced by symmetry to couple to the other fields as a dilaton; the effective metric it yields on the NEC violating solution is that of de Sitter space, so that all light scalars will automatically acquire a nearly scale-invariant spectrum of perturbations.
We compute the universal generic corrections to the inflationary power spectrum due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the ``in-in'' formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. We find that the power spectrum is universally modified at order $H/M$, where $H$ is the scale of inflation. Since this ratio is optimistically estimated to be $10^{-2}$, a precision obtainable by upcoming experiments, this suggests that it may soon be possible to extract details of high-energy physics, including the first signals of quantum gravity.
In this paper we study the effect of the channeling of ions recoiling from collisions with weakly interacting massive particles (WIMPs) in single crystal detectors. In particular we investigate the possibility that channeling may give rise to diurnal modulations of the counting rate as the Earth rotates relative to the direction of the WIMP wind, and the effect that channeling has on the "quenching factor" of a detector.
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