The Planck experiment will soon provide a very accurate measurement of Cosmic Microwave Background anisotropies. This will let cosmologists determine most of the cosmological parameters with unprecedented accuracy. Future experiments will improve and complement the Planck data with better angular resolution and better polarization sensitivity. This unexplored region of the CMB power spectrum contains information on many parameters of interest, including neutrino mass, the number of relativistic particles at recombination, the primordial Helium abundance and the injection of additional ionizing photons by dark matter self-annihilation. We review the imprint of each parameter on the CMB and forecast the constraints achievable by future experiments by performing a Monte Carlo analysis on synthetic realizations of simulated data. We find that next generation satellite missions such as CMBPol could provide valuable constraints with a precision close to that expected in current and near future laboratory experiments. Finally, we discuss the implications of this intersection between cosmology and fundamental physics.
Dark energy is an important science driver of many upcoming large-scale surveys. With small, stable seeing and low thermal infrared background, Dome A, Antarctica, offers a unique opportunity for shedding light on fundamental questions about the universe. We show that a deep, high-resolution imaging survey of 10,000 square degrees in \emph{ugrizyJH} bands can provide competitive constraints on dark energy equation of state parameters using type Ia supernovae, baryon acoustic oscillations, and weak lensing techniques. Such a survey may be partially achieved with a coordinated effort of the Kunlun Dark Universe Survey Telescope (KDUST) in \emph{yJH} bands over 5000--10,000 deg$^2$ and the Large Synoptic Survey Telescope in \emph{ugrizy} bands over the same area. Moreover, the joint survey can take advantage of the high-resolution imaging at Dome A to further tighten the constraints on dark energy and to measure dark matter properties with strong lensing as well as galaxy--galaxy weak lensing.
We present wide-field Herschel/PACS observations of Abell 1689, a massive galaxy cluster at z=0.1832, from our Open Time Key Programme. We detect 39 spectroscopically confirmed 100micron-selected cluster members down to 1.5x10^10 Lsun. These galaxies are forming stars at rates in the range 1-10 Msun/yr, and appear to comprise two distinct populations: two-thirds are unremarkable blue, late-type spirals found throughout the cluster; the remainder are dusty red sequence galaxies whose star formation is heavily obscured with A(Halpha)~2 mag, and are found only in the cluster outskirts. The specific-SFRs of these dusty red galaxies are lower than the blue late-types, suggesting that the former are in the process of being quenched, perhaps via pre-processing, the unobscured star formation being terminated first. We also detect an excess of 100micron-selected galaxies extending ~6 Mpc in length along an axis that runs NE-SW through the cluster centre at >95% confidence. Qualitatively this structure is consistent with previous reports of substructure in X-ray, lensing, and near-infrared maps of this cluster, further supporting the view that this cluster is a dynamically active, merging system.
We present Herschel/PACS, MMT/Hectospec and XMM-Newton observations of Abell 1835, one of the brightest X-ray clusters on the sky, and the host of a strong cool core. Even though Abell 1835 has a prototypically "relaxed" X-ray morphology and no signs of ongoing merger activity in strong- and weak-lensing mass maps, it has a complex velocity distribution, suggesting that it is still accreting significant amounts of mass in the form of smaller satellite systems. Indeed, we find strong dynamical segregation of star-forming dusty galaxies from the optically selected cluster population. Most Herschel sources are found close to the virial radius of the cluster, and almost a third appear to be embedded within a filament feeding the cluster from the SW. We find that the most luminous infrared galaxies are likely involved in galaxy-galaxy interactions that may have triggered the current phase of star formation.
In the coming decade, low-frequency radio arrays will begin to probe the epoch of reionization via the redshifted 21-cm hydrogen line. Successful interpretation of these observations will require effective statistical techniques for analyzing the data. Due to the difficulty of these measurements, it is important to develop techniques beyond the standard power spectrum analysis in order to offer independent confirmation of the reionization history, probe different aspects of the topology of reionization, and have different systematic errors. In order to assess the promise of probability distribution functions (PDFs) as statistical analysis tools in 21-cm cosmology, we first measure the 21-cm brightness temperature (one-point) PDFs in six different reionization simulations. We then parametrize their most distinct features by fitting them to a simple model. Using the same simulations, we also present the first measurements of difference PDFs in simulations of reionization. We find that while these statistics probe the properties of the ionizing sources, they are relatively independent of small-scale, sub-grid astrophysics. We discuss the additional information that the difference PDF can provide on top of the power spectrum and the one-point PDF.
We present an early broad-brush analysis of Herschel/PACS observations of star-forming galaxies in 8 galaxy clusters drawn from our survey of 30 clusters at z~0.2. We define a complete sample of 192 spectroscopically confirmed cluster members down to L_TIR>3x10^10L_sun and L_K>0.25L_sun. The average K-band and bolometric infrared luminosities of these galaxies both fade by a factor of ~2 from clustercentric radii of 2r_200 to ~0.5r_200, indicating that as galaxies enter the clusters ongoing star-formation stops first in the most massive galaxies, and that the specific star-formation rate (SSFR) is conserved. On smaller scales the average SSFR jumps by 25%, suggesting that in cluster cores processes including ram pressure stripping may trigger a final episode of star-formation that presumably exhausts the remaining gas. This picture is consistent with our comparison of the Herschel-detected cluster members with the cluster mass distributions, as measured in our previous weak-lensing study of these clusters. For example, the spatial distribution of the Herschel sources is positively correlated with the structures in the weak-lensing mass maps at 5sigma significance, with the strongest signal seen at intermediate group-like densities. The strong dependence of the total cluster IR luminosity on cluster mass L_TIR propto M_virial^2 is also consistent with accretion of galaxies and groups of galaxies (i.e. the substructure mass function) driving the cluster IR luminosity. The most surprising result is that roughly half of the Herschel-detected cluster members have redder S_100/S_24 flux ratios than expected, based on the Rieke et al. models. On average cluster members are redder than non-members, and the fraction of red galaxies increases towards the cluster centers, both of which indicate that these colors are not attributable to systematic photometric errors. [Abridged]
We report spectroscopic confirmation and high-resolution infrared imaging of a z=2.79 triply-imaged galaxy behind the Bullet Cluster. This source, a Spitzer-selected luminous infrared galaxy (LIRG), is confirmed via polycyclic aromatic hydrocarbon (PAH) features using the Spitzer Infrared Spectrograph (IRS) and resolved with HST WFC3 imaging. In this galaxy, which is likely the least massive one studied with IRS at z>2, we also detect H_2 S(4) and H_2 S(5) pure rotational lines (at 3.1 sigma and 2.1 sigma) - the first detection of these molecular hydrogen lines in a high-redshift galaxy. From the molecular hydrogen lines we infer an excitation temperature T=377+68-84 K. The detection of these lines implies a substantial reservoir of molecular gas, indicating that future spectral observations at longer wavelengths with facilities like the Herschel Space Observatory, the Large Millimeter Telescope, and the Atacama Pathfinder EXperiment (APEX) hold the promise of precisely determining the temperature and molecular gas mass in the galaxy. Given the redshift, and using refined astrometric positions from the high resolution imaging, we also update the magnification estimate and derived fundamental physical properties of this system. The previously published values for total infrared luminosity, star formation rate, and dust temperature are confirmed modulo the revised magnification; however we find that PAH emission is roughly a factor of five stronger than would be predicted by the relations between the total infrared and PAH luminosity reported for SMGs and starbursts in Pope et al. (2008).
The Herschel Lensing Survey (HLS) will conduct deep PACS and SPIRE imaging of ~40 massive clusters of galaxies. The strong gravitational lensing power of these clusters will enable us to penetrate through the confusion noise, which sets the ultimate limit on our ability to probe the Universe with Herschel. Here, we present an overview of our survey and a summary of the major results from our Science Demonstration Phase (SDP) observations of the Bullet Cluster (z=0.297). The SDP data are rich, allowing us to study not only the background high-redshift galaxies (e.g., strongly lensed and distorted galaxies at z=2.8 and 3.2) but also the properties of cluster-member galaxies. Our preliminary analysis shows a great diversity of far-infrared/submillimeter spectral energy distributions (SEDs), indicating that we have much to learn with Herschel about the properties of galaxy SEDs. We have also detected the Sunyaev-Zel'dovich (SZ) effect increment with the SPIRE data. The success of this SDP program demonstrates the great potential of the Herschel Lensing Survey to produce exciting results in a variety of science areas.
The Herschel Lensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100-500 micron bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 micron and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 micron selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities.This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales.
We use deep, five band (100-500um) data from the Herschel Lensing Survey (HLS) to fully constrain the obscured star formation rate, SFR_FIR, of galaxies in the Bullet cluster (z=0.296), and a smaller background system (z=0.35) in the same field. Herschel detects 23 Bullet cluster members with a total SFR_FIR = 144 +/- 14 M_sun yr^-1. On average, the background system contains brighter far-infrared (FIR) galaxies, with ~50% higher SFR_FIR (21 galaxies; 207 +/- 9 M_sun yr^-1). SFRs extrapolated from 24um flux via recent templates (SFR_24) agree well with SFR_FIR for ~60% of the cluster galaxies. In the remaining ~40%, SFR_24 underestimates SFR_FIR due to a significant excess in observed S_100/S_24 (rest frame S_75/S_18) compared to templates of the same FIR luminosity.
We present preliminary results about the detection of high redshift (U)LIRGs in the Bullet cluster field by the PACS and SPIRE instruments within the Herschel Lensing Survey (HLS) Program. We describe in detail a photometric procedure designed to recover robust fluxes and deblend faint Herschel sources near the confusion noise. The method is based on the use of the positions of Spitzer/MIPS 24 um sources as priors. Our catalogs are able to reliably (5 sigma) recover galaxies with fluxes above 6 and 10 mJy in the PACS 100 and 160 um channels, respectively, and 12 to 18 mJy in the SPIRE bands. We also obtain spectral energy distributions covering the optical through the far-infrared/millimeter spectral ranges of all the Herschel detected sources, and analyze them to obtain independent estimations of the photometric redshift based on either stellar population or dust emission models. We exemplify the potential of the combined use of Spitzer position priors plus independent optical and IR photometric redshifts to robustly assign optical/NIR counterparts to the sources detected by Herschel and other (sub-)mm instruments.
The Sunyaev-Zel'dovich (SZ) effect is a spectral distortion of the cosmic microwave background as observed through the hot plasma in galaxy clusters. This distortion is a decrement in the CMB intensity for lambda > 1.3 mm, an increment at shorter wavelengths, and small again by lambda ~250 um. As part of the Herschel Lensing Survey (HLS) we have mapped 1E0657-56 (the Bullet cluster) with SPIRE with bands centered at 250, 350 and 500 um and have detected the SZ effect at the two longest wavelengths. The measured SZ effect increment central intensities are Delta I_{0} = 0.097 +- 0.019 MJy sr^{-1} at 350 um and Delta I_{0} = 0.268 +- 0.031 MJy sr^{-1} at 500 um, consistent with the SZ effect spectrum derived from previous measurements at 2 mm. No other diffuse emission is detected. The presence of the finite temperature SZ effect correction is preferred by the SPIRE data at a significance of 2.1 sigma, opening the possibility that the relativistic SZ effect correction can be constrained by SPIRE in a sample of clusters. The results presented here have important ramifications for both sub-mm measurements of galaxy clusters and blank field surveys with SPIRE.
Ultra-luminous infrared galaxies are among the most luminous objects in the local universe and are thought to be powered by intense star formation. It has been shown that in these objects the rotational spectral lines of molecular hydrogen observed at mid-infrared wavelengths are not affected by dust obscuration, leaving unresolved the source of excitation of this emission. Here I report an analysis of archival Spitzer Space Telescope data on ultra-luminous infrared galaxies and demonstrate that star formation regions are buried inside optically thick clouds of gas and dust, so that dust obscuration affects star-formation indicators but not molecular hydrogen. I thereby establish that the emission of H_2 is not co-spatial with the buried starburst activity and originates outside the obscured regions. This is rather surprising in light of the standard view that H_2 emission is directly associated with star-formation activity. Instead, I propose that H_2 emission in these objects traces shocks in the surrounding material, which are in turn excited by interactions with nearby galaxies, and that powerful large-scale shocks cooling by means of H_2 emission may be much more common than previously thought. In the early universe, a boost in H_2 emission by this process may speed up the cooling of matter as it collapsed to form the first stars and galaxies and would make these first structures more readily observable.
The Bullet Cluster is a massive galaxy cluster at z=0.297 undergoing a major supersonic merger event. Using Spitzer MIPS 24um and IRAC data, with optical imaging and spectroscopy, we present the global star formation rate (SFR) of this unique cluster. Using a 90% spectroscopically complete sample of 39 MIPS confirmed cluster members out to R<1.7 Mpc, we find an integrated SFR of 282 Msolar/yr and a specific SFR of 30 Msolar/yr/10^14 Msolar. The integrated SFR per cluster mass of the Bullet Cluster is among the highest in a sample of eight cluster and cluster mergers from the literature. Five LIRGs and one ULIRG contribute 25% and 40% of the total SFR of the cluster, respectively. To investigate the origin of the elevated specific SFR, we compare the infrared luminosity function (IR LF) of the Bullet Cluster to those of Coma and CL1358+62. The good general agreement between the cluster LFs imply that the major merger event in the Bullet Cluster has not had a dramatic effect on obscured star formation and is likely not the cause of the high specific SFR relative to other clusters. We do however observe an excess of sources in the bright end of the Bullet Cluster IR LF due to the LIRG and ULIRG population, which is not observed in Coma or CL1358+62. A Schechter function fit of the Bullet Cluster IR LF yields L*=44.70+/-0.16, which is 0.25 and 0.35 dex brighter than L* of Coma and CL1358+62, respectively. We attribute the bright end excess of the Bullet Cluster IR LF to a population associated with the infalling group that have not yet been transformed into quiescent galaxies. In this case, the timescale required for quenching star formation in the cluster environment must be longer than the timescale since the group's accretion -- a few hundred million years. We suggest that ``strangulation'' is likely to be an important process in the evolution of star formation in clusters.
We present a study of the average properties of luminous infrared galaxies detected directly at 24 $\mu$m in the COSMOS field using a median stacking analysis at 70$\mu$m and 160 $\mu$m. Over 35000 sources spanning 0<z<3 and 0.06 mJy<S_{24}<3.0 mJy are stacked, divided into bins of both photometric redshift and 24 $\mu$m flux. We find no correlation of $S_{70}/S_{24}$ flux density ratio with $S_{24}$, but find that galaxies with higher $S_{24}$ have a lower $S_{160}/S_{24}$ flux density ratio. These observed ratios suggest that 24 $\mu$m selected galaxies have warmer SEDs at higher mid-IR fluxes, and therefore have a possible higher fraction of AGN. Comparisons of the average $S_{70}/S_{24}$ and $S_{160}/S_{24}$ colors with various empirical templates and theoretical models show that the galaxies detected at 24 $\mu$m are consistent with "normal" star-forming galaxies and warm mid-IR galaxies such as Mrk 231, but inconsistent with heavily obscured galaxies such as Arp 220. We perform a $\chi^{2}$ analysis to determine best fit galactic model SEDs and total IR luminosities for each of our bins. We compare our results to previous methods of estimating $L_{\rm{IR}}$ and find that previous methods show considerable agreement over the full redshift range, except for the brightest $S_{24}$ sources, where previous methods overpredict the bolometric IR luminosity at high redshift, most likely due to their warmer dust SED. We present a table that can be used as a more accurate and robust method for estimating bolometric infrared luminosity from 24 $\mu$m flux densities.
We present images of extended H-alpha clouds associated with 14 member galaxies in the Coma cluster obtained from deep narrow band imaging observations with Suprime-Cam at the Subaru Telescope. The parent galaxies of the extended H-alpha clouds are distributed farther than 0.2 Mpc from the peak of X-ray emission of the cluster. Most of the galaxies have colors bluer than g-r approx 0.5 and they account for 57% of the blue (g-r<0.5) bright (r<17.8 mag) galaxies in the central region of the Coma cluster. They reside near the red- and blue-shifted edges of the Coma cluster's radial velocity distribution. These findings suggest that the most of the parent galaxies were recently captured by the Coma cluster potential and are now infalling toward the cluster center with their disk gas being stripped off and producing the observed H-alpha clouds.
This is the second paper in our completeness series which addresses some of the issues raised in the previous article by Johnston, Teodoro & Hendry (2007) in which we developed statistical tests for assessing the completeness in apparent magnitude of magnitude-redshift surveys defined by two flux limits. The statistics, Tc and Tv, associated with these tests are non-parametric and defined in terms of the observed cumulative distribution function of sources; they represent powerful tools for identifying the true flux limit and/or characterising systematic errors in magnitude-redshift data. In this paper we present a new approach to constructing these estimators that resembles an "adaptive smoothing" procedure - i.e. by seeking to maintain the same amount the information, as measured by the signal-to-noise ratio, allocated to each galaxy. For consistency with our previous work, we apply our improved estimators to the Millennium Galaxy Catalogue (MGC) and the Two Degree Field Galaxy Redshift Survey (2dFGRS) data, and demonstrate that one needs to use a signal-to-noise appropriately tailored for each individual catalogue to optimise the performance of the completeness estimators. Furthermore, unless such an adaptive procedure is employed, the assessment of completeness may result in a spurious outcome if one uses other estimators present in the literature which have not been designed taking into account "shot noise" due to sampling.
We present a stellar population synthesis study of a type I luminous infrared galaxy (LIRG): IRAS F13308+5946. It is a quasar with absolute magnitude Mi = -22.56 and has a spectral feature of a Seyfert 1.5 galaxy. Optical images show characteristics of later stages of a merger. With the help of the stellar synthesis code STARLIGHT (Cid Fernandes et al. 2005) and both Calzetti et al. (2000) and Leitherer et al.'s (2002) extinction curves, we estimate the past infrared (IR) luminosities of the host galaxy and find it may have experienced an ultraluminous infrared galaxy (ULIRG) phase for nearly 300 Myr, so this galaxy has probably experienced a type I ULIRG phase. Both nuclear starburst and active galactic nuclei (AGN) contribute to the present IR luminosity budget, and starburst contributes ~70%. The mass of supermassive black-hole (SMBH) is M_BH = 1.8*10^8 M_sun and the Eddington ratio L_bol/L_Edd is 0.12, which both approximate to typical values of PG QSOs. These results indicate that IRAS F13308+5946 is probably at the transitional phase from a type I ULIRG to a classical QSO.
We use a suite of cosmological, hydrodynamical simulations to investigate the chemical enrichment history of the Universe. Specifically, we trace the origin of the metals back in time to investigate when various gas phases were enriched and by what halo masses. We find that the age of the metals decreases strongly with the density of the gas in which they end up. At least half of the metals that reside in the diffuse intergalactic medium (IGM) at redshift zero (two) were ejected from galaxies above redshift two (three). The mass of the haloes that last contained the metals increases rapidly with the gas density. More than half of the mass in intergalactic metals was ejected by haloes with total masses less than 1e11 solar masses and stellar masses less than 1e9 solar masses. The range of halo masses that contributes to the enrichment is wider for the hotter part of the IGM. By combining the `when' and `by what' aspects of the enrichment history, we show that metals residing in lower density gas were typically ejected earlier and by lower mass haloes.
We find a unique direction in the CMB sky around which giant rings have an anomalous mean temperature profile. This direction is in very close alignment with the afore measured anomalously large bulk flow direction. We argue that a cosmic defect seeded by a pre-inflationary particle could explain the giant rings, the large bulk flow and their alignment.
Particle creation at the expense of Gravitational field might be sufficient to explain the cosmic evolution history, without the need of dark energy at all. This phenomena has been investigated in the present work extending recent works of Lima et-al (Class.Quantum.Grav.25, (2008) 205006).
Current analyses of the Lyman-alpha forest assume that the primordial power spectrum of density perturbations obeys a simple power law, a strong theoretical assumption which should be tested. Employing a large suite of numerical simulations which drop this assumption, we reconstruct the shape of the primordial power spectrum using Lyman-alpha data from the Sloan Digital Sky Survey (SDSS). Our method combines a minimally parametric framework with cross-validation, a technique used to avoid over-fitting the data. Future work will involve predictions for the upcoming Baryon Oscillation Sky Survey (BOSS), which will provide new Lyman-alpha data with vastly decreased statistical errors.
GW Notes was born from the need for a journal where the distinct communities involved in gravitation wave research might gather. While these three communities - Astrophysics, General Relativity and Data Analysis - have made significant collaborative progress over recent years, we believe that it is indispensable to future advancement that they draw closer, and that they speak a common idiom. For this GW Notes issue we have approached Miguel Preto (Heidelberg University) to expand a recent work on how stars distribute around massive black holes for our highlight article.
We estimate large-scale curvature perturbations from isocurvature fluctuations in the waterfall field during hybrid inflation, in addition to the usual inflaton field perturbations. The tachyonic instability at the end of inflation leads to an explosive growth of super-Hubble scale perturbations, but they retain the steep blue spectrum characteristic of vacuum fluctuations in a massive field during inflation. The power spectrum thus peaks around the Hubble-horizon scale at the end of inflation. We extend the usual delta-N formalism to include the essential role of these small fluctuations when estimating the large-scale curvature perturbation. The resulting curvature perturbation due to fluctuations in the waterfall field is second-order and the spectrum is expected to be of order 10^{-54} on cosmological scales.
We present the evolution of the full set of Einstein equations during preheating after inflation. We study a generic supersymmetric model of hybrid inflation, integrating fields and metric fluctuations in a 3-dimensional lattice. We take initial conditions consistent with Eintein's constraint equations. The induced preheating of the metric fluctuations is not large enough to backreact onto the fields, but preheating of the scalar modes does affect the evolution of vector and tensor modes. In particular, they do enhance the induced stochastic background of gravitational waves during preheating, giving an energy density in general an order of magnitude larger than that obtained by evolving the tensors fluctuations in an homogeneous background metric. This enhancement can improve the expectations for detection by planned gravitational waves observatories.
We derive accurate semi-analytic formulae for the power spectra of two-field inflation assuming an arbitrary potential and arbitrary non-canonical kinetic terms, and we use them both to build phenomenological intuition and to constrain classes of two-field models using WMAP data. Using covariant formalism, we first develop a framework for understanding the background field kinematics and introduce a "slow-turn" approximation. We then find covariant expressions for the evolution of the field perturbations, both in the given basis and in the basis in which the fluctuations decompose into adiabatic and entropy modes. Next, we derive second-order expressions for the curvature, isocurvature, and cross spectra, and their spectral indices. The covariant formalism we use provides useful intuition for how general features of the inflationary Lagrangian translate into distinct features in the observable power spectra. In particular, we find that key features of the power spectra can be directly read off from the nature of the roll path, the curve the field vector rolls along with respect to the two-dimensional field manifold. For example, models whose roll path makes a sharp turn around 60 e-foldings before the end of inflation tend to be ruled out because they produce stronger departures from scale invariance than are allowed by the latest CMB observations. This makes our combined slow-roll/slow-turn approximation very useful in practice, since models that violate the approximation tend to be irrelevant by virtue of already being ruled out. Finally, we apply our formalism to confront four classes of two-field models with WMAP data, including doubly quadratic and quartic potentials and non-standard kinetic terms, showing how whether a model is ruled out or not depends not only on the inflationary Lagrangian, but also on the initial conditions.
We use a sample of newly-discovered globular clusters from the Pan-Andromeda Archaeological Survey (PAndAS) in combination with previously-catalogued objects to map the spatial distribution of globular clusters in the M31 halo. At projected radii beyond ~30 kpc, where large coherent stellar streams are readily distinguished in the field, there is a striking correlation between these features and the positions of the globular clusters. Adopting a simple Monte Carlo approach, we test the significance of this association by computing the probability that it could be due to the chance alignment of globular clusters smoothly distributed in the M31 halo. We find the likelihood of this possibility is low, below 1%, and conclude that the observed spatial coincidence between globular clusters and multiple tidal debris streams in the outer halo of M31 reflects a genuine physical association. Our results imply that the majority of the remote globular cluster system of M31 has been assembled as a consequence of the accretion of cluster-bearing satellite galaxies. This constitutes the most direct evidence to date that the outer halo globular cluster populations in some galaxies are largely accreted.
We report the first X-ray detection of 113 Lyman-alpha emitters at redshift z ~ 4.5. Only one source (J033127.2-274247) is detected in the Extended Chandra Deep Field South (ECDF-S) X-ray data, and has been spectroscopically confirmed as a z = 4.48 quasar with $L_X = 4.2\times 10^{44}$ erg/s. The single detection gives a Lyman-alpha quasar density consistent with the X-ray luminosity function of quasars. The coadded counts of 22 Lyman-alpha emitters (LAEs) in the central Chandra Deep Field South (CDF-S) region yields a S/N=2.4 (p=99.83%) detection at soft band, with an effective exposure time of ~36 Ms. Further analysis of the equivalent width (EW) distribution shows that all the signal comes from 12 LAE candidates with EW_rest < 400 \AA, and 2 of them contribute about half of the signal. Following-up spectroscopic observations show that the two are a low-redshift emission line galaxy and a Lyman break galaxy at z = 4.4. Excluding these two and combined with ECDF-S data, we derive a 3-sigma upper limit on the average luminosity of $L_{0.5-2 keV}$ $<$ 2.4 $\times 10^{42}$ ergs/s for z ~ 4.5 LAEs. If the average X-ray emission is due to star formation, it corresponds to a star-formation rate (SFR) of < 180--530 M$_\sun$ per yr. We use this SFR_X as an upper limit of the unobscured SFR to constrain the escape fraction of Lyman-alpha photons, and find a lower limit of f_esc > 3-10%. However, our upper limit on the SFR_X is ~7 times larger than the upper limit on SFR_X on z ~ 3.1 LAEs in the same field, and at least 30 times higher than the SFR estimated from Lyman-alpha emission. From the average X-ray to Lyman-alpha line ratio, we estimate that fewer than 3.2% (6.3%) of our LAEs could be high redshift type 1 (type 2) AGNs, and those hidden AGNs likely show low rest frame EWs.
In this work we study the effects of field space curvature on scalar field perturbations around an arbitrary background field trajectory evolving in time. Non-trivial imprints of the `heavy' directions arise when the vacuum manifold of the potential does not coincide with the span of geodesics defined by the sigma model metric of the low energy effective theory. When the kinetic energy is small compared to the potential energy, the field traverses a curve close to the vacuum manifold of the potential. The curvature of the trajectory can still have a profound influence on the perturbations as modes parallel to the trajectory mix with those normal to the trajectory if the trajectory turns sharply enough. These effects could be important during inflation, which could lead to detectable effects in upcoming observations.
The work presented in this paper aims at restricting the input parameter values of the semi-analytical model used in GALICS and MOMAF, so as to derive which parameters influence the most the results, e.g., star formation, feedback and halo recycling efficiencies, etc. Our approach is to proceed empirically: we run lots of simulations and derive the correct ranges of values. The computation time needed is so large, that we need to run on a grid of computers. Hence, we model GALICS and MOMAF execution time and output files size, and run the simulation using a grid middleware: DIET. All the complexity of accessing resources, scheduling simulations and managing data is harnessed by DIET and hidden behind a web portal accessible to the users.
Four lectures on Big Bang cosmology, including microwave background radiation, Big Bang nucleosynthesis, dark matter, inflation, and baryogenesis.
We investigate the nature of the host galaxies of long Gamma-Ray bursts (LGRBs) using a galaxy catalogue constructed from the Millennium Simulation. We developed an LGRB synthetic model based on the hypothesis that LGRBs originate at the end of the life of massive stars following the collapsar model, optionally including a constraint on the metallicity of the progenitor. An observability pipeline was designed to reproduce observations from BATSE experiment and to include a probability estimation for a galaxy to be observationally identified as a host. This new tool allows us to build an observable host galaxy catalogue, required to reproduce the current stellar mass distribution of observed hosts. Systems in our observable catalogue are able to reproduce the observed properties of host galaxies, namely stellar masses, colours, luminosity, star formation activity and metallicities as a function of redshift. At z>2, our model predicts that the observable host galaxies would be very similar to the global galaxy population. We found that ~87 per cent of the observable host galaxies with mean gas metallicity lower than 0.6 solar have stellar masses in the range 10^8.5-10^10.3 solar masses in agreement with observations. Interestingly, observable host galaxies remain mainly within this mass range regardless of redshift, since lower stellar mass systems would have a low probability of being observed while more massive ones would be too metal-rich. Observable host galaxies are predicted to preferentially inhabit dark matter haloes of 10^11-10^11.5 solar masses, with a weak dependence on redshift. They are also found to preferentially map different density environments at different redshifts. At high redshifts, the observable host galaxies are predicted to be located in similar environments as the global galaxy population but to have a slightly higher probability to have a close companion.
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Observations of the frequency dependence of the global brightness temperature of the redshifted 21 cm line of neutral hydrogen may be possible with single dipole experiments. In this paper, we develop a Fisher matrix formalism for calculating the sensitivity of such instruments to the 21 cm signal from reionization and the dark ages. We show that rapid reionization histories with duration delta z< 2 can be constrained, provided that local foregrounds can be well modelled by low order polynomials. It is then shown that observations in the range nu = 50 - 100 MHz can feasibly constrain the Lyman alpha and X-ray emissivity of the first stars forming at z = 15 - 25, provided that systematic temperature residuals can be controlled to less than 1 mK. Finally, we demonstrate the difficulty of detecting the 21 cm signal from the dark ages before star formation.
We study the growth of dark matter halos in the concordance LCDM cosmology using several N-body simulations of large cosmological volumes. We build merger trees from the Millennium and Millennium-II simulations, covering a range 10^9-10^15 Msun in halo mass and 1-10^5 in merger mass ratio. Our algorithm takes special care of halo fragmentation and ensures that the mass contribution of each merger to halo growth is only counted once. This way the integrated merger rate converges and we can consistently determine the contribution of mergers of different mass ratios to halo growth. We find that all resolved mergers, up to mass ratios of 10^5, contribute only ~60% of the total halo mass growth, while major mergers are subdominant, e.g. mergers with mass ratios smaller than 3:1 (10:1) contribute only ~20% (~30%). This is verified with an analysis of two additional simulation boxes, where we follow all particles individually throughout cosmic time. Our results are also robust against using several halo definitions. Under the assumption that the power-law behaviour of the merger rate at large mass ratios can be extrapolated to arbitrarily large mass ratios, it is found that, independently of halo mass, ~40% of the mass in halos comes from genuinely smooth accretion of dark matter that was never bound in smaller halos. We discuss possible implications of our findings for galaxy formation. One robust implication, under standard assumptions about pre-heating from UV phot ons, is that all halos accrete >40% of their baryons in smooth T<~10^4K gas.
We present Swift UVOT (1600-3000A) 3-band photometry for 41 galaxies in 11 nearby (<4500km/s) Hickson Compact Groups (HCGs) of galaxies. We use the uvw2-band (2000A) to estimate the dust-unobscured component, SFR_UV, of the total star-formation rate, SFR_T. We use Spitzer MIPS 24-micron photometry to estimate SFR_IR, the dust-obscured component of SFR_T. We obtain SFR_T=SFR_UV+SFR_IR. Using 2MASS K_s band based stellar mass, M*, estimates, we calculate specific SFRs, SSFR=SFR_T/M*. SSFR values show a clear and significant bimodality, with a gap between low (<~3.2x10^-11 / yr) and high SSFR (>~1.2x10^-10 / yr) systems. All galaxies with MIR activity index a_IRAC <= 0 (>0) are in the high- (low-) SSFR locus, as expected if high levels of star-formation power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. All elliptical/S0 galaxies are in the low-SSFR locus, while 22 out of 24 spirals/irregulars are in the high-SSFR locus, with two borderline cases. We divide our sample into three subsamples (I, II and III) according to decreasing HI-richness of the parent galaxy group to which a galaxy belongs. Consistent with the SSFR and a_IRAC bimodality, 12 out of 15 type-I (11 out of 12 type-III) galaxies are in the high- (low-) SSFR locus, while type II galaxies span almost the full range of SSFR values. Unlike HCG galaxies, galaxies in a comparison quiescent SINGS sub-sample are continuously distributed both in SSFR and a_IRAC. Any uncertainties can only further enhance the SSFR bimodality. These results suggest that an environment characterized by high galaxy number-densities and low galaxy velocity-dispersions, such as the one found in compact groups, plays a key role in accelerating galaxy evolution by enhancing star-formation processes in galaxies and favoring a fast transition to quiescence.(abridged)
We study the peculiar velocities of density peaks in the presence of primordial non-Gaussianity. Rare, high density peaks in the initial density field can be identified with tracers such as galaxies and clusters in the evolved matter distribution. The distribution of relative velocities of peaks is derived in the large-scale limit using two different approaches based on a local biasing scheme. Both approaches agree, and show that halos still stream with the dark matter locally as well as statistically, i.e. they do not acquire a velocity bias. Nonetheless, even a moderate degree of (not necessarily local) non-Gaussianity induces a significant skewness (~ 0.1-0.2) in the relative velocity distribution, making it a potentially interesting probe of non-Gaussianity on intermediate to large scales. We also study two-point correlations in redshift-space. The well-known Kaiser formula is still a good approximation on large scales, if the Gaussian halo bias is replaced with its (scale-dependent) non-Gaussian generalization. However, there are additional terms not encompassed by this simple formula which become relevant on smaller scales (k >~ 0.01 h/Mpc). Depending on the allowed level of non-Gaussianity, these could be of relevance for future large spectroscopic surveys.
Cosmological hydrodynamic simulations robustly predict that high-redshift galaxy star formation histories (SFHs) are smoothly-rising and vary with mass only by a scale factor. We use our latest simulations to test whether this scenario can account for recent observations at z>=6 from WFC3/IR, NICMOS, and IRAC. Our simulations broadly reproduce the observed ultraviolet (UV) luminosity functions and stellar mass densities and their evolution at z=6-8, all of which are nontrivial tests of the mean SFH. In agreement with observations, simulated galaxies possess blue UV continua owing to young ages (50-150 Myr), low metallicities (0.1-0.5 Zsun), and low dust columns (E(B-V) <= 0.05). Observations imply a near-unity slope in the stellar mass--star formation rate relation at all z=6-8, confirming the prediction that SFH shapes are invariant. Current surveys detect the majority of galaxies with stellar masses exceeding 10^9 Msun and few galaxies less massive than 10^{8.5} Msun, implying that they probe no more than the brightest 30% of the complete star formation and stellar mass densities at z>=6. Finally, we demonstrate that there is no conflict between smoothly-rising SFHs and recent clustering observations. This is because momentum-driven outflows suppress star formation in low-mass halos, leading to overall occupancies of 0.2-0.4 even though the star formation duty cycle is one. This leads to many interesting predictions at z>=4, among them that (1) optically-selected and UV-selected samples largely overlap; (2) few galaxies exhibit significantly suppressed specific star formation rates; and (3) occupancy is constant or increasing with decreasing luminosity. These predictions are in tentative agreement with current observations, but further analysis of existing and upcoming data sets is required in order to test them more thoroughly. (abridged)
We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is obtaining slitless, near-infrared grism spectroscopy of ~ 90 independent, high-latitude fields by observing in the pure parallel mode with Wide Field Camera-3 on the Hubble Space Telescope for a total of ~ 250 orbits. Spectra are obtained with the G102 (lambda=0.8-1.17 microns, R ~ 210) and G141 grisms (lambda=1.11-1.67 microns, R ~ 130), together with direct imaging in the J- and H-bands (F110W and F140W, respectively). In the present paper, we present the first results from 19 WISP fields, covering approximately 63 square arc minutes. For typical exposure times (~ 6400 sec in G102 and ~ 2700 sec in G141), we reach 5-sigma detection limits for emission lines of 5 x 10^(-17) ergs s^(-1) cm^(-2) for compact objects. Typical direct imaging 5sigma-limits are 26.8 and 25.0 magnitudes (AB) in F110W and F140W, respectively. Restricting ourselves to the lines measured with highest confidence, we present a list of 328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The single-line emitters are likely to be a mix of Halpha and [OIII]5007,4959 A, with Halpha predominating. The overall surface density of high-confidence emission-line objects in our sample is approximately 4 per arcmin^(2).These first fields show high equivalent width sources, AGN, and post starburst galaxies. The median observed star formation rate of our Halpha selected sample is 4 Msol/year. At intermediate redshifts, we detect emission lines in galaxies as faint as H_140 ~ 25, or M_R < -19, and are sensitive to star formation rates down to less than 1 Msol/year. The slitless grisms on WFC3 provide a unique opportunity to study the spectral properties of galaxies much fainter than L* at the peak of the galaxy assembly epoch.
The \hi 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources ($\gtrsim 1$ ~Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array (MWA). We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky-model for bright sources, as well as frequency independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the \hi power spectrum. For calibration errors, 0.05 % accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, $\kperp \gtrsim 0.05 $Mpc$^{-1}$, in the two-dimensional power spectrum.
Recent observational data on the type Ia supernova rates are in excellent agreement with the old prediction of the population synthesis of binary stars and confirm that the overwhelming majority of type Ia supernovas (~99%) in elliptical galaxies form via mergers of binary white dwarfs with the total mass exceeding the Chandrasekhar limit.
Non-congruence appears to be the most general form of phase transition in cosmic matter and in the laboratory. In terrestrial applications noncongruencemeans coexistence of phases with different chemical composition in systems consisting of two (or more) chemical elements. It is just the case for all phase transitions in high-temperature chemically reactive mixtures, which are typical for uranium-bearing compounds in many nuclear energy devices, both contemporary and perspective. As for cosmic matter, most of real and hypothetical phase transitions without nuclear reactions, i.e., those in the interiors of giant planets (solar and extrasolar), those in brown dwarfs and other sub-stellar objects, as well as in the outer crust of compact stars, are very plausible candidates for such type of phase transformations. Two exotic phase transitions, the gas-liquid phase transition in dense nuclear matter and the quark-hadron transition occuring in the interior of compact stars as well as in high-energy heavy-ion collisions are under discussion as the most extreme example of hypothetical non-congruence for phase transformations in High Energy Density Matter.
We study the emission of X-rays from lobes of FR-II radio galaxies by inverse Compton scattering of microwave background photons. Using a simple model that takes into account injection of relativistic electrons, their energy losses through adiabatic expansion, synchrotron and inverse Compton emission, and also the stopping of the jet after a certain time, we study the evolution of the total X-ray power, the surface brightness, angular size of the X-ray bright region and the X-ray photon index, as functions of time and cocoon size, and compare the predictions with observations. We find that the radio power drops rapidly after the stopping of the jet, with a shorter time-scale than the X-ray power. The X-ray spectrum initially hardens until the jet stops because the steepening of electron spectrum is mitigated by the injection of fresh particles, for electrons with $\gamma \ge 10^3$. This happens because of the concurrence of two times scales, that of the typical jet lifetimes and cooling due to inverse Compton scattering ($\sim 10^{7\hbox{--}8}$ yr), of electrons responsible for scattering CMB photons into keV range photons (with $\gamma \sim \sqrt{1 \, {\rm keV}/ kT_{CMB}}$). Another finding is that the ratio of the X-ray to radio power is a robust parameter that varies mostly with redshift and ambient density, but is weakly dependent on other parameters. We also determine the time-averaged ratio of X-ray to radio luminosities (at 1 keV and 151 MHz) and find that it scales with redshift as $\propto (1+z)^{3.8}$, for typical values of parameters. We then estimate the X-ray luminosity function of FR-II radio galaxies and estimate the number of these diffuse X-ray bright objects above a flux limit of $\sim 3 \times 10^{-16}$ erg cm$^{-2}$ s$^{-1}$ to be $\sim 25$ deg$^{-2}$.
We investigate the nature of Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context, simultaneously accounting for various "classical" dSphs and Milky Way (MW) properties, including their Metallicity Distribution Function (MDF). The model successfully reproduces both the observed [Fe/H]-Luminosity relation and the mean MDF of UFs. According to our results UFs are the living fossils of H2-cooling minihaloes formed at z>8.5, i.e. before the end of reionization. They are the oldest and the most dark matter-dominated (M/L > 100) dSphs in the MW system, with a total mass of M = 10^(7-8) Msun. The model allows to interpret the different shape of UFs and classical dSphs MDF, along with the frequency of extremely metal-poor stars in these objects. We discuss the "missing satellites problem" by comparing the UF star formation efficiencies with those derived for minihaloes in the Via Lactea simulation.
Extended HI structures around galaxies are of prime importance to probe galaxy formation scenarios. The giant HI ring in the Leo group is one of the largest and most intriguing HI structures in the nearby Universe. Whether it consists of primordial gas, as suggested by the apparent absence of any optical counterpart and the absence of an obvious physical connection to nearby galaxies, or of gas expelled from a galaxy in a collision is actively debated. We present deep wide field-of-view optical images of the ring region obtained with MegaCam on the CFHT. They reveal optical counterparts to several HI and UV condensations along the ring, in the g', r', and i' bands, which likely correspond to stellar associations formed within the gaseous ring. Analyzing the spectral energy distribution of one of these star-forming regions, we found it to be typical for a star-forming region in pre-enriched tidal debris. We then use simulations to test the hypothesis that the Leo ring results from a head-on collision between Leo group members NGC 3384 and M96. According to our model which is able to explain, at least qualitatively, the main observational properties of the system, the Leo ring is consistent with being a collisional ring. It is thus likely another example of extended intergalactic gas made-up from pre-enriched collisional debris.
We report the results of multicolour observations of 30 E/S0 galaxies with dust lanes. For each galaxy we obtained broad-band images and narrow-band images using interference filters isolating the H\alpha +[NII] emission lines to derive the amount and morphology of dust and ionized gas. To improve the wavelength coverage we retrieved data from the SDSS and 2MASS and combined these with our data. Ionized gas is detected in 25 galaxies and shows in most cases a smooth morphology, although knots and filamentary structure are also observed in some objects. The extended gas distribution closely follows the dust structure, with a clear correlation between the mass of both components. An extinction law by the extragalactic dust in the dark lanes is derived and is used to estimate the dust content of the galaxies. The derived extinction law is used to correct the measured colours for intrinsic dust extinction and the data are fitted with a stellar population synthesis model. We find that the H-alpha emission and colours of most objects are consistent with the presence of an "old" stellar population (~10 Gyr) and a small fraction of a "young" population (~10-100 Myr). To check this we closely examine NGC5363, for which archival Spitzer/IRAC and GALEX data are available, as a representative dust-lane E/S0 galaxy of the sample.
We describe in detail the general methodology and numerical implementation of consistent N-body simulations for coupled scalar field cosmological models, including the background cosmology and the generation of initial conditions (with the different couplings to different matter species taken into account). We perform fully consistent simulations for a class of coupled scalar field models with an inverse power-law potential and negative coupling constant, for which the chameleon mechanism does not operate. We find that in such cosmological models the scalar-field potential plays a negligible role except in the background expansion, and the fifth force that is produced is proportional to gravity in magnitude, justifying the use of a rescaled gravitational constant G in some earlier N-body simulations of similar models. We study the effects of the scalar coupling on the nonlinear matter power spectra and compare with linear perturbation calculations to investigate where the nonlinear model deviates from the linear approximation. For the first time, the algorithm to identify gravitationally virialized matter halos is adapted to the scalar field cosmology, and then used to measure the mass function and study the properties of virialized halos. We find that the net effect of the scalar coupling helps produce more heavy halos in our simulation boxes and suppresses the inner (but not the outer) density profile of halos compared with those predicted by lambda-CDM, while this suppression weakens as the coupling between the scalar field and dark matter particles increases in strength.
We construct a simple, spherical blastwave model to estimate the pressure structure of the intergalactic medium surrounding hyper-starburst galaxies, and argue that the effects of interaction with star-forming galaxy winds may be approximated at early times by an adiabatically expanding, self-similar `bubble' as described by Weaver et al. (1977) and Ostriker & McKee (1988). This model is used to make observational predictions for the thermal Sunyaev-Zel'dovich effect in the shocked bubble plasma. Radiative cooling losses are explored, and it is found that bremsstrahlung will limit the epoch of adiabatic expansion to $10^7$--$10^8$ years: comparable to total hyper-starburst lifetimes. Prospects for making a first Sunyaev-Zel'dovich detection of galaxy wind bubbles using the Atacama Large Millimeter Array are examined for a number of active hyper-starburst sources in the literature.
Spitzer and AKARI observations have found that polycyclic aromatic hydrocarbons (PAHs) are present in nearby elliptical galaxies, but their spatial distributions are still unknown. In order to investigate their distributions, we performed deep spectral mapping observations of the PAH-detected elliptical galaxy NGC4589, a merger remnant with a minor-axis optical dust lane. As a result, we obtain clear evidence that the PAH 11.3 um emission comes predominantly from the dust lane of the galaxy. We also detect molecular hydrogen line emissions from the dust lane. The PAH 17 um emission is distributed differently from the PAH 11.3 um emission, and more similarly to the dust continuum emission. From their distinctive distributions, we suggest that the PAHs responsible for the 11.3 um feature are secondary products through the evolution of the ISM brought in by the merger.
We apply the Constitution compilation of 397 supernova Ia, the baryon acoustic oscillation measurements including the $A$ parameter, the distance ratio and the radial data, the five-year Wilkinson Microwave Anisotropy Probe and the Hubble parameter data to study the geometry of the universe and the property of dark energy by using the popular Chevallier-Polarski-Linder and Jassal-Bagla-Padmanabhan parameterizations. We compare the simple $\chi^2$ method of joined contour estimation and the Monte-Carlo Markov Chain method, and find that it is necessary to make the marginalized analysis on the error estimation. The probabilities of $\Omega_k$ and $w_a$ in the Chevallier-Polarski-Linder model are skew distributions, and the marginalized $1\sigma$ errors are $\Omega_m=0.279^{+0.015}_{-0.008}$, $\Omega_k=0.005^{+0.006}_{-0.011}$, $w_0=-1.05^{+0.23}_{-0.06}$, and $w_a=0.5^{+0.3}_{-1.5}$. For the Jassal-Bagla-Padmanabhan model, the marginalized $1\sigma$ errors are $\Omega_m=0.281^{+0.015}_{-0.01}$, $\Omega_k=0.000^{+0.007}_{-0.006}$, $w_0=-0.96^{+0.25}_{-0.18}$, and $w_a=-0.6^{+1.9}_{-1.6}$. The equation of state parameter $w(z)$ of dark energy is negative in the redshift range $0\le z\le 2$ at more than $3\sigma$ level. The flat $\Lambda$CDM model is consistent with the current observational data at $1\sigma$ level.
Recent measurements of hot and cold spots on the cosmic microwave background (CMB) sky suggest a presence of super-structures on (>100 h^{-1}Mpc) scales. We develop a new formalism to estimate the expected amplitude of temperature fluctuations due to the integrated Sachs-Wolfe (ISW) effect from prominent quasi-linear structures. Applying the developed tools to the observed ISW signals from voids and clusters in catalogs of galaxies at redshifts z<1, we find that they indeed imply a presence of quasi-linear super-structures with a comoving radius 100~300 h^{-1}Mpc and a density contrast ~O(0.1). We find that the observed ISW signals are at odd with the concordant \Lambda cold dark matter (CDM) model that predicts Gaussian primordial perturbations at equal to or larger than 3 sigma level. We also confirm that the mean temperature around the CMB cold spot in the southern Galactic hemisphere filtered by a compensating top-hat filter deviates from a mean value at ~3 sigma level, implying that a quasi-linear supervoid or an underdensity region surrounded by a massive wall may reside at low redshifts z<0.3 and the actual angular size (16^\circ-17^\circ) may be larger than the apparent size (4^\circ-10^\circ) discussed in literature. Possible solutions are briefly discussed.
We propose an estimator defined in real space for the reconstruction of the weak lensing potential due to the intervening large scale structure from high resolution maps of the cosmic microwave background. This estimator was motivated as an alternative to the quadratic estimator in harmonic space to surpass the difficulties of the analysis of maps containing galactic cuts and point source excisions. Using maps synthesised by pixel remapping, we implement the estimator for two experiments, namely one in the absence and one in the presence of detector noise, and compare the reconstruction of the convergence field with that obtained with the quadratic estimator defined in harmonic space. We find good agreement between the input and the reconstructed power spectra using the proposed real space estimator. We discuss interesting features of the real space estimator and future extensions of this work.
We investigate the cosmic age problem associated with 9 extremely old globular clusters in M31 galaxy and 1 very old high-$z$ quasar APM 08279 + 5255 at $z=3.91$. Notice that these 9 globular clusters have not been used to study the cosmic age problem in the previous literature. By evaluating the age of the universe in the $\Lambda$CDM model with the observational constraints from the SNIa, the BAO, the CMB, and the independent $H_0$ measurements, we find that the existence of 5 globular clusters and 1 high-$z$ quasar are in tension (over 2$\sigma$ confidence level) with the current cosmological observations. So if the age estimates of these objects are correct, the cosmic age puzzle still remains in the standard cosmology. Moreover, we extend our investigations to the cases of the interacting dark energy models. It is found that although the introduction of the interaction between dark sectors can give a larger cosmic age, the interacting dark energy models still have difficulty to pass the cosmic age test.
We present the optical spectra of a sample of 41 SWIRE-CDFS observed with EFOSC2 on the ESO 3.6m Telescope. We have used the spectra and spectroscopic redshifts to validate our photometric redshift codes and SED template fitting methods. 19 of our sources are Infrared Luminous Galaxies. Of these, five belong to the class of ULIRGs with evidence of both an AGN and starburst component contributing to their extreme infrared luminosity in 80% of them. All ULIRGs exhibit broad line features in their optical spectra.
The low frequency tail of the CMB spectrum, down along the radio range (~1 GHz), may carry weak spectral distortions which are fingerprints of processes occurred during different epochs of the thermal history of the Universe, from z~3\times 10^6 to reionization. TRIS and ARCADE2 are the most recent experiments dedicated to the exploration of this chapter of CMB cosmology. The level of instrumental accuracy they reached in the determination of the absolute sky temperature is such that the removal of galactic and extra-galactic contamination is the true bottleneck towards the recovery of the cosmological signal. This will be certainly the case also for future experiments in the radio domain. Here we present an update of a study originally done to recognize the contribution of unresolved extra-galactic radio sources to the sky brightness measured by TRIS. Despite the specific context which originated our analysis, this is a study of general interest, improved by the inclusion of all the source counts available up-to-date from 150 MHz to 8.4 GHz.
We attempt a slingshot model interpretation of the unusual association of some 1&1/3 dozen nonstellar galaxian objects around the parent optical galaxy of the giant radio galaxy DA 240 (= 0748.6+55.8 (J2000)). Similar interpretation may be possible for another large radio galaxy 3C 31 (= NGC 383 = 0104.6+32.1 (1950.0)).
In this work we applied Soldner's classical approach for bending of light in the context of \emph{Newtonian corpuscular theory}. We show that there is a good evidence for existence of a massive photon in new scenario of gravity due to Verlinde[17].
In loop quantum cosmology, the Hamiltonian reduces to a finite difference operator. We study the initial singularity and the large volume limit against the ambiguities in the discretisation and the operator ordering within a homogeneous, isotropic and spatially flat model with the cosmological constant. We find that the absence of the singularity strongly depends on the choice of the operator ordering and the requirement for the absence singles out a very small class of orderings. Moreover we find a general ordering rule required for the absence of the singularity. We also find that the large volume limit naturally recovers a smooth wave function in the discretisation where each step corresponds to a fixed volume increment but not in the one where each step corresponds to a fixed area increment. If loop quantum cosmology is to be a phenomenological realisation of full loop quantum gravity, these results are important to fix the theoretical ambiguities.
The spectral triple approach to noncommutative geometry allows one to develop the entire standard model (and supersymmetric extensions) of particle physics from a purely geometry stand point and thus treats both gravity and particle physics on the same footing. The bosonic sector of the theory contains a modification to Einstein-Hilbert gravity, involving a nonconformal coupling of curvature to the Higgs field and conformal Weyl term (in addition to a nondynamical topological term). In this paper we derive the weak field limit of this gravitational theory and show that the production and dynamics of gravitational waves are significantly altered. In particular, we show that the graviton contains a massive mode that alters the energy lost to gravitational radiation, in systems with evolving quadrupole moment. We explicitly calculate the general solution and apply it to systems with periodically varying quadrupole moments, focusing in particular on the the well know energy loss formula for circular binaries.
The noncommutative spectral action extends our familiar notion of commutative spaces, using the data encoded in a spectral triple on an almost commutative space. Varying a rather simple action, one can derive all of the standard model of particle physics in this setting, in addition to a modified version of Einstein-Hilbert gravity. Thus, noncommutative geometry provides a geometric interpretation of particle physics coupled to curvature. In this letter we use observations of pulsar timings, assuming that no deviation from General Relativity has been observed, to constrain the gravitational sector of this theory. Thus, we directly constrain noncommutative geometry, a potential grand unified theory of physics, via astrophysical observations. Whilst the bounds on the coupling constants remain rather weak, they are comparable to existing bounds on deviations from General Relativity in other settings and are likely to be further constrained by future observations.
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Recently Menard et al. (hereafter MSFR) detected a subtle but systematic change in the mean color of quasars as a function of their projected separation from foreground galaxies, extending to comoving separations of ~ 10\hMpc, which they interpret as a signature of reddening by intergalactic dust. We present theoretical models of this remarkable observation, using smoothed particle hydrodynamic (SPH) cosmological simulations of a (50\hMpc)^3 volume. Our primary model uses a simulation with galactic winds and assumes that dust traces the intergalactic metals. The predicted galaxy-dust correlation function is similar in form to the galaxy-mass correlation function, and reproducing the MSFR data requires a dust-to-metal mass ratio of 0.24, about half the value in the Galactic ISM. Roughly half of the reddening arises in dust that is more than 100\hKpc from the nearest massive galaxy. We also examine a simulation with no galactic winds, which predicts a much smaller fraction of intergalactic metals (3% vs. 35%) and therefore requires an unphysical dust-to-metal ratio of 2.18 to reproduce the MSFR data. The no-wind simulation can be reconciled with the data if we also allow reddening to arise in galaxies up to several X 10^10 Msun. The wind model predicts a mean visual extinction of <A_V> ~ 0.005 mag out to z=0.5, with a sightline-to-sightline dispersion similar to the mean, which could be significant for future supernova cosmology studies. Reproducing the MSFR results in these simulations requires that a large fraction of ISM dust survive its expulsion from galaxies and its residence in the intergalactic medium. Future observational studies that provide higher precision and measure the dependence on galaxy type and environment will allow detailed tests for models of enriched galactic outflows and the survival of intergalactic dust.
We study perturbations in the multi-field axion Nflation model, taking account of the full cosine potential. We find significant differences with previous analyses which made a quadratic approximation to the potential. The tensor-to-scalar ratio and the scalar spectral index move to lower values, which nevertheless provide an acceptable fit to observation. More importantly, we find that the bispectrum non-gaussianity parameter f_NL may be large, typically of order 10 for moderate values of the axion decay constant, increasing to of order 100 for decay constants slightly smaller than the Planck scale. Such a non-gaussian fraction is detectable. We argue that this property is generic in multi-field models of hilltop inflation.
Galactic outflows of low ionization, cool gas are ubiquitous in local
starburst galaxies, and in the majority of galaxies at high redshift. How these
cool outflows arise is still in question. Hot gas from supernovae has long been
suspected as the primary driver, but this mechanism suffers from its tendency
to destroy the cool gas as the latter is accelerated. We propose a modification
of the supernova scenario that overcomes this difficulty.
Star formation is observed to take place in clusters; in a given galaxy, the
bulk of the star formation is found in the ~20 most massive clusters. We show
that, for L* galaxies, the radiation pressure from clusters with M>10^6 M_sun
is able to expel the surrounding gas at velocities in excess of the circular
velocity of the disk galaxy. This cool gas can travel above the galactic disk
in less than 2 Myr, well before any supernovae erupt in the driving cluster.
Once above the disk, the cool outflowing gas is exposed to radiation, and
supernovae induced hot gas outflows, from other clusters in the disk, which
drive it to distances of several tens to hundreds of kpc. Because the
radiatively driven clouds grow in size as they travel, and because the hot gas
is more dilute at large distance, the clouds are less subject to destruction if
they do eventually encounter hot gas. Therefore, unlike wind driven clouds,
radiatively driven clouds can survive to distances ~50 kpc. We identify these
cluster-driven winds with large-scale galactic outflows. Another implication of
our model is that only starburst galaxies, where massive clusters reside, are
able to drive winds cold outflows on galactic scales via this mechanism. We
find that the critical star formation rates above which large scale cool
outflows will be launched to be ~0.1 M_sun/yr/kpc^2, which is in good agreement
with observations.
With the aim of determining if Milky Way (MW) progenitors could be identified as high redshift Lyman Alpha Emitters (LAEs) we have derived the intrinsic properties of z ~ 5.7 MW progenitors, which are then used to compute their observed Lyman-alpha luminosity, L_alpha, and equivalent width, EW. MW progenitors visible as LAEs are selected according to the canonical observational criterion, L_alpha > 10^42 erg/s and EW > 20 A. Progenitors of MW-like galaxies have L_alpha = 10^(39-43.25) erg/s, making some of them visible as LAEs. In any single MW merger tree realization, typically only 1 (out of ~ 50) progenitor meets the LAE selection criterion, but the probability to have at least one LAE is very high, P = 68%. The identified LAE stars have ages, t_* ~ 150-400 Myr at z ~ 5.7 with the exception of five small progenitors with t_* < 5 Myr and large EW = 60-130 A. LAE MW progenitors provide > 10% of the halo very metal-poor stars [Fe/H] < -2, thus establishing a potentially fruitful link between high-z galaxies and the Local Universe.
Measuring the full three-dimensional motions of extra-galactic objects in the Universe presents a seemingly insurmountable challenge. In this paper we investigate the application of a technique to measure tangential motion that has previously only been applied nearby within the Local Group of galaxies, to clusters of galaxies far beyond its borders. We show that mapping the mean line-of-sight motion throughout a galaxy cluster could in principle be used to detect the "perspective rotation" induced by the projection of the cluster's tangential motion into the line-of-sight. The signal will be most prominent for clusters of the largest angular extent, most symmetric intrinsic velocity distribution and surveyed with the largest number of pointings possible. We investigate the feasibility of detecting this signal using three different approaches: measuring line-of-sight motions of individual cluster members; taking spectra of intracluster gas; and mapping distortions of the Cosmic Microwave Background radiation. We conclude that future spectroscopic surveys of 1000's of members of nearby galaxy clusters hold the most promise of measuring cluster tangential motions using this technique.
We introduce the TANAMI program (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) which is monitoring an initial sample of 43 extragalactic jets located south of -30 degrees declination at 8.4 GHz and 22 GHz since 2007. All aspects of the program are discussed. First epoch results at 8.4 GHz are presented along with physical parameters derived therefrom. We present first epoch images for 43 sources, some observed for the first time at milliarcsecond resolution. Parameters of these images as well as physical parameters derived from them are also presented and discussed. These and subsequent images from the TANAMI survey are available at this http URL We obtain reliable, high dynamic range images of the southern hemisphere AGN. All the quasars and BL Lac objects in the sample have a single-sided radio morphology. Galaxies are either double-sided, single-sided or irregular. About 28% of the TANAMI sample has been detected by LAT during its first three months of operations. Initial analysis suggests that when galaxies are excluded, sources detected by LAT have larger opening angles than those not detected by LAT. Brightness temperatures of LAT detections and non-detections seem to have similar distributions. The redshift distributions of the TANAMI sample and sub-samples are similar to those seen for the bright gamma-ray AGN seen by LAT and EGRET but none of the sources with a redshift above 1.8 have been detected by LAT.
In this letter we propose a new and model-independent cosmological test for the distance-duality (DD) relation, $\eta=D_{L}(z)(1+z)^{-2}/D_{A}(z)=1$, where $D_{L}$ and $D_{A}$ are, respectively, the luminosity and angular diameter distances. For $D_L$ we consider two sub-samples of SNe type Ia taken from Constitution data (2009) whereas $D_A$ distances are provided by two samples of galaxy clusters compiled by De Fillipis {\it et al.} (2005) and Bonamente {\it et al.} (2006) by combining Sunyaev-Zeldovich effect (SZE) and X-ray surface brightness. The SNe Ia redshifts of each sub-sample were carefully chosen to coincide with the ones of the associated galaxy cluster sample ($\Delta z<0.005$) thereby allowing a direct test of DD relation. Since for very low redshifts, $D_{A}(z) \approxeq D_{L}(z)$, we have tested the DD relation by assuming that $\eta$ is a function of the redshift parametrized by two different expressions: $\eta(z) = 1 + \eta_{0}z$ and $\eta(z) = 1 + \eta_{0}z/(1+z)$, where $\eta_0$ is a constant parameter quantifying a possible departure from the strict validity of the reciprocity relation ($\eta_0=0$). In the best scenario (linear parametrization) we obtain $\eta_{0} = -0.28^{+ 0.3}_{- 0.3}$ ($2\sigma$) for de Fillipis {\it et al.} sample (eliptical geometry), a result only marginally compatible with the DD relation. However, for Bonamente {\it et al.} sample (spherical geometry) the constraint is $\eta_{0} = -0.41^{+ 0.3}_{- 0.3}$ ($3\sigma$) which is clearly incompatible with the duality-distance relation.
We selected a sample of 24 XMM-Newton light curves (LCs) of four high energy peaked blazars, PKS 0548-322, ON 231, 1ES 1426+428 and PKS 2155-304. These data comprise continuous light curves of 7.67h to 18.97h in length. We searched for possible quasi-periodic oscillations (QPO) and intra-day variability (IDV) timescales in the LCs of these blazars. We found a likely QPO in one LC of PKS 2155-304 which was reported elsewhere (Lachowicz et al. 2009). In the remaining 23 LCs we found hints of possible weak QPOs in one LC of each of ON 231 and PKS 2155-304, but neither is statistically significant. We found IDV timescales that ranged from 15.7 ks to 46.8 ks in 8 LCs. In 13 LCs any variability timescales were longer than the length of the data. Assuming the possible weak QPO periods in the blazars PKS 2155-304 and ON 231 are real and are associated with the innermost portions of their accretion disk, we can estimate that their central black hole masses exceed 1.2 $\times$ 10$^{7}$ M$_{\odot}$. Emission models for radio-loud active galactic nuclei (AGN) that could explain our results are briefly discussed.
By observing mergers of compact objects, future gravity wave experiments would measure the luminosity distance to a large number of sources to a high precision but not their redshifts. Given the directional sensitivity of an experiment, a fraction of such sources (gold plated -- GP) can be identified optically as single objects in the direction of the source. We show that if an approximate distance-redshift relation is known then it is possible to statistically resolve those sources that have multiple galaxies in the beam. We study the feasibility of using gold plated sources to iteratively resolve the unresolved sources, obtain the self-calibrated best possible distance-redshift relation and provide an analytical expression for the accuracy achievable. We derive lower limit on the total number of sources that is needed to achieve this accuracy through self-calibration. We show that this limit depends exponentially on the beam width and give estimates for various experimental parameters representative of future gravitational wave experiments DECIGO and BBO.
We compare the sensitivity of a recent bound on time variation of the fine structure constant from optical clocks with bounds on time varying fundamental constants from atomic clocks sensitive to the electron-to-proton mass ratio, from radioactive decay rates in meteorites, and from the Oklo natural reactor. Tests of the Weak Equivalence Principle also lead to comparable bounds on present time variations of constants, as well as putting the strongest limits on variations tracking the gravitational potential. For recent time variations, the "winner in sensitivity" depends on possible relations between the variations of different couplings in the standard model of particle physics. WEP tests are currently the most sensitive within scenarios with unification of gauge interactions. A detection of time variation in atomic clocks would favour dynamical dark energy and put strong constraints on the dynamics of a cosmological scalar field.
We explore the cosmological evolution in the exponential gravity $f(R)=R +c_1 \left(1-e^{- c_2 R} \right)$ ($c_{1, 2} = \mathrm{constant}$). We summarize various viability conditions and explicitly demonstrate that the late-time cosmic acceleration following the matter-dominated stage can be realized. We also study the equation of state for dark energy and confirm that the crossing of the phantom divide from the phantom phase to the non-phantom (quintessence) one can occur. Furthermore, we illustrate that the cosmological horizon entropy globally increases with time.
We point out an interesting theoretical prediction for elliptical galaxies residing inside galaxy clusters in the framework of modified Newtonian dynamics (MOND), that could be used to test this paradigm. Apart from the central brightest cluster galaxy, other galaxies close enough to the centre experience a strong gravitational influence from the other galaxies of the cluster. This influence manifests itself only as tides in standard Newtonian gravity, meaning that the systematic acceleration of the centre of mass of the galaxy has no consequence. However, in the context of MOND, a consequence of the breaking of the strong equivalence principle is that the systematic acceleration changes the own self-gravity of the galaxy. We show here that, in this framework, initially axisymmetric elliptical galaxies become lopsided along the external field's direction, and that the centroid of the galaxy, defined by the outer density contours, is shifted by a few hundreds parsecs with respect to the densest point.
We review the main advances brought by the Spitzer Space Telescope in the field of nearby galaxies studies, concentrating on a few subject areas, including: (1) the physics of the Polycyclic Aromatic Hydrocarbons that generate the mid-infrared features between ~3.5 micron and ~20 micron; (2) the use of the mid- and far-infrared emission from galaxies as star formation rate indicators; and (3) the improvement of mid-infrared diagnostics to discriminate between thermal (star-formation) and non-thermal (AGN) emission in galaxies and galaxy centers.
For finite chemical potential effective models of QCD predict a first order phase transition. In favour for the search of such a phase transition in nature, we construct an equation of state for strange quark matter based on the MIT bag model. We apply this equation of state to highly asymmetric core collapse supernova matter with finite temperatures and large baryon densities. The phase transition is constructed using the general Gibbs conditions, which results in an extended coexistence region between the pure hadronic and pure quark phases in the phase diagram, i.e. the mixed phase. The supernovae are simulated via general relativistic radiation hydrodynamics based on three flavor Boltzmann neutrino transport in spherical symmetry. During the dynamical evolution temperatures above 10 MeV, baryon densities above nuclear saturation density and a proton-to-baryon ratio below 0.2 are obtained. At these conditions the phase transition is triggered which leads to a significant softening of the EoS for matter in the mixed phase. As a direct consequence of the stiffening of the EoS again for matter in the pure quark phase, a shock wave forms at the boundary between the mixed and the pure hadronic phases. This shock is accelerated and propagates outward which releases a burst of neutrinos dominated by electron anti-neutrinos due to the lifted degeneracy of the shock-heated hadronic material. We discuss the radiation-hydrodynamic evolution of the phase transition at the example of several low and intermediate mass Fe-core progenitor stars and illustrate the expected neutrino signal from the phase transition.
We discuss the additional perturbation introduced during inflation by quantum stress tensor fluctuations of a conformally invariant field such as the photon. We consider both a kinematical model, which deals only with the expansion fluctuations of geodesics, and a dynamical model which treats the coupling of the stress tensor fluctuations to a scalar inflaton. In neither model do we find any growth at late times, in accordance with a theorem due to Weinberg. What we find instead is a correction which becomes larger the earlier one starts inflation. This correction is non-Gaussian and highly scale dependent, so the absence of such effects from the observed power spectra may imply a constraint on the total duration of inflation. We discuss different views about the validity of perturbation theory at very early times during which currently observable modes are transplanckian.
We show that the chiral-limit vacuum quark condensate is qualitatively equivalent to the pseudoscalar meson leptonic decay constant in the sense that they are both obtained as the chiral-limit value of well-defined gauge-invariant hadron-to-vacuum transition amplitudes that possess a spectral representation in terms of the current-quark mass. Thus, whereas it might sometimes be convenient to imagine otherwise, neither is essentially a constant mass-scale that fills all spacetime. This means, in particular, that the quark condensate can be understood as a property of hadrons themselves, which is expressed, for example, in their Bethe-Salpeter or light-front wavefunctions.
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We present deep J and Ks band photometry of 20 high redshift galaxy clusters between z=0.8-1.5, 19 of which are observed with the MOIRCS instrument on the Subaru Telescope. By using near-infrared light as a proxy for stellar mass we find the surprising result that the average stellar mass of Brightest Cluster Galaxies (BCGs) has remained constant at ~9e11MSol since z~1.5. We investigate the effect on this result of differing star formation histories generated by three well known and independent stellar population codes and find it to be robust for reasonable, physically motivated choices of age and metallicity. By performing Monte Carlo simulations we find that the result is unaffected by any correlation between BCG mass and cluster mass in either the observed or model clusters. The large stellar masses imply that the assemblage of these galaxies took place at the same time as the initial burst of star formation. This result leads us to conclude that dry merging has had little effect on the average stellar mass of BCGs over the last 9-10 Gyr in stark contrast to the predictions of semi-analytic models, based on the hierarchical merging of dark matter haloes, which predict a more protracted mass build up over a Hubble time. We discuss however that there is potential for reconciliation between observation and theory if there is a significant growth of material in the intracluster light over the same period.
The next generation mass probes will obtain information on non--linear power
spectra P(k,z) and their evolution, allowing us to investigate the nature of
Dark Energy. To exploit such data we need high precision simulations, extending
at least up to scales of k\simeq 10 h^-1 Mpc, where the effects of baryons can
no longer be neglected.
In this paper, we present a series of large scale hydrodynamical simulations
for LCDM and dynamical Dark Energy (dDE) models, in which the equation of state
parameter is z-dependent. The simulations include gas cooling, star formation
and Supernovae feedback. They closely approximate the observed star formation
rate and the observationally derived star/Dark Matter mass ratio in collapsed
systems. Baryon dynamics cause spectral shifts exceeding 1% at k > 2-3 hMpc^-1
compared to pure n-body simulations in the LCDM simulations. This agrees with
previous studies, although we find a smaller effect (~50%) on the power
spectrum amplitude at higher k's. dDE exhibits similar behavior, even though
the dDE simulations produce ~20% less stars than the analogous LCDM
cosmologies. Finally, we show that the technique introduced in Casarini et al.
to obtain spectra for any $w(z)$ cosmology from constant-w models at any
redshift still holds when gas physics is taken into account. While this
relieves the need to explore the entire functional space of dark energy state
equations, we illustrate a severe risk that future data analysis could lead to
misinterpretation of the DE state equation.
We present an analysis of the host galaxy dependencies of Type Ia Supernovae (SNe Ia) from the full three year sample of the SDSS-II Supernova Survey. We rediscover, to high significance, the strong correlation between host galaxy typeand the width of the observed SN light curve, i.e., fainter, quickly declining SNe Ia favor passive host galaxies, while brighter, slowly declining Ia's favor star-forming galaxies. We also find evidence (at between 2 to 3 sigma) that SNe Ia are ~0.1 magnitudes brighter in passive host galaxies, than in star-forming hosts, after the SN Ia light curves have been standardized using the light curve shape and color variations: This difference in brightness is present in both the SALT2 and MCLS2k2 light curve fitting methodologies. We see evidence for differences in the SN Ia color relationship between passive and star-forming host galaxies, e.g., for the MLCS2k2 technique, we see that SNe Ia in passive hosts favor a dust law of R_V ~1, while SNe Ia in star-forming hosts require R_V ~2. The significance of these trends depends on the range of SN colors considered. We demonstrate that these effects can be parameterized using the stellar mass of the host galaxy (with a confidence of >4 sigma) and including this extra parameter provides a better statistical fit to our data. Our results suggest that future cosmological analyses of SN Ia samples should include host galaxy information.
We investigate the role of stellar mass in shaping the intrinsic thickness of galaxy discs by determining the probability distribution of apparent axis ratios (b/a) for two different samples that probe the faint end of the galaxy luminosity function. We find that the b/a distribution has a characteristic 'U-shape' and identify a limiting mass M_* ~ 2x10^9 M_sun below which low-mass galaxies start to be systematically thicker. This tendency holds for very faint (M_B ~ -8) dwarfs in the Local Volume, which are essentially spheroidal systems. We argue that galaxy shape is the result of the complex interplay between mass, specific angular momentum and stellar feedback effects. Thus, the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems, a result supported by the latest hydrodynamical simulations of dwarf galaxy formation and other theoretical expectations. We discuss several implications of this finding, including the formation of bars in faint galaxies, the deprojection of HI line profiles and simulations of environmental effects on the dwarf galaxy population.
We study large-scale winds from self-gravitating disks radiating near the Eddington limit. We show that the ratio of the radiation pressure force to the gravitational force increases with height to a maximum of twice its value at the disk surface. Thus, self-gravitating disks radiating near the Eddington limit are fundamentally unstable to driving large-scale winds. This result stands in stark contrast to the spherically symmetric case, where super-Eddington luminosities are required for wind formation. We apply this theory to galactic winds from starburst galaxies that approach the Eddington limit for dust. For hydrodynamically coupled gas and dust, we find that the asymptotic velocity of the wind is v_infinity ~ 2 v_esc, and that v_infinity ~ SFR^{0.36}, where v_esc is the escape velocity and SFR is the star formation rate. Both relations are in excellent agreement with observations. We estimate the minimum SFR surface density required for wind formation and the wind mass loss rate Mdot in the "single-scattering" limit. The latter implies efficient gas expulsion for low-mass galaxies. We evaluate the effects of both a spherical dark matter halo and an (old) stellar bulge potential. At fixed disk Eddington ratio, both the halo and bulge act to decrease v_infinity and Mdot, causing the wind to become bound and form a "fountain flow" with a typical turning timescale of ~0.1-1 Gyr. Thus, bulge formation and halo assembly may halt efficient wind formation, with implications for the growth of galaxies over cosmic time, as well as the metal content of galaxies and the intergalactic medium.
We use Chandra X-ray and Spitzer infrared observations to explore the AGN and starburst populations of XMMXCS J2215.9-1738 at z=1.46, one of the most distant spectroscopically confirmed galaxy clusters known. The high resolution X-ray imaging reveals that the cluster emission is contaminated by point sources that were not resolved in XMM observations of the system, and have the effect of hardening the spectrum, leading to the previously reported temperature for this system being overestimated. From a joint spectroscopic analysis of the Chandra and XMM data, the cluster is found to have temperature T=4.1_-0.9^+0.6 keV and luminosity L_X=(2.92_-0.35^+0.24)x10^44 erg/s extrapolated to a radius of 2 Mpc. As a result of this revised analysis, the cluster is found to lie on the sigma_v-T relation, but the cluster remains less luminous than would be expected from self-similar evolution of the local L_X-T relation. Two of the newly discovered X-ray AGN are cluster members, while a third object, which is also a prominent 24 micron source, is found to have properties consistent with it being a high redshift, highly obscured object in the background. We find a total of eight >5 sigma 24 micron sources associated with cluster members (four spectroscopically confirmed, and four selected using photometric redshifts), and one additional 24 micron source with two possible optical/near-IR counterparts that may be associated with the cluster. Examining the IRAC colors of these sources, we find one object is likely to be an AGN. Assuming that the other 24 micron sources are powered by star formation, their infrared luminosities imply star formation rates ~100 M_sun/yr. We find that three of these sources are located at projected distances of <250 kpc from the cluster center, suggesting that a large amount of star formation may be taking place in the cluster core, in contrast to clusters at low redshift.
We present an analysis of an 8 arcminute diameter map of the area around the galaxy cluster Abell 1835 from jiggle map observations at a wavelength of 1.1 mm using the Bolometric Camera (Bolocam) mounted on the Caltech Submillimeter Observatory (CSO). The data is well described by a model including an extended Sunyaev-Zel'dovich (SZ) signal from the cluster gas plus emission from two bright background submm galaxies magnified by the gravitational lensing of the cluster. The best-fit values for the central Compton value for the cluster and the fluxes of the two main point sources in the field: SMM J140104+0252, and SMM J14009+0252 are found to be $y_{0}=(4.34\pm0.52\pm0.69)\times10^{-4}$, 6.5$\pm{2.0}\pm0.7$ mJy and 11.3$\pm{1.9}\pm1.1$ mJy, where the first error represents the statistical measurement error and the second error represents the estimated systematic error in the result. This measurement assumes the presence of dust emission from the cluster's central cD galaxy of $1.8\pm0.5$ mJy, based on higher frequency observations of Abell 1835. The cluster image represents one of the highest-significance SZ detections of a cluster in the positive region of the thermal SZ spectrum to date. The inferred central intensity is compared to other SZ measurements of Abell 1835 and this collection of results is used to obtain values for $y_{0} = (3.60\pm0.24)\times10^{-4}$ and the cluster peculiar velocity $v_{z} = -226\pm275$ km/s.
We present near-infrared (NIR) spectroscopy for 37 BzK-color-selected star-forming galaxies with MOIRCS on Subaru. The sample is drawn from the Ks-band selected catalog of the MOIRCS Deep Survey (MODS) in the GOODS-N region. About half of our samples are selected from the MIPS 24um-source catalog. Ha emission lines are detected from 23 galaxies, of which the median redshift is 2.12. We derived the star formation rates (SFRs) from extinction-corrected Ha luminosities. The extinction correction is estimated from the SED fitting of multi-band photometric data covering UV to NIR wavelengths. The Balmer decrement of the stacked emission lines shows that the amount of extinction for the ionized gas is larger than that for the stellar continuum. From a comparison of the extinction corrected Ha luminosity and other SFR indicators we found that the relation between the dust properties of stellar continuum and ionized gas is different depending on the intrinsic SFR. The comparison between the Ha SFR and stellar mass estimated from SED fitting shows no correlation between them. Some galaxies with stellar mass smaller than ~10^10 Msun show SFRs higher than ~100 Msun/yr. The specific SFRs (SSFRs) of these galaxies are remarkably high. The average stellar-population age of these high-SSFR galaxies is younger than 100 Myr, which is consistent with the implied high SSFR. The large SFR implies the possibility that the high SSFR galaxies significantly contribute to the cosmic SFR density of the universe at z~2. The total SFR density estimated from the Ha emission line galaxies is 0.089-0.136 Msun/yr/Mpc^3, which is consistent with the total SFR densities in the literature. The metallicity of the high-SSFR galaxies is larger than that expected from the mass-metallicity relation of UV-selected galaxies at z~2 by Erb et al. (2006a). [Abridged]
It is found that \feii emission contributes significantly to the optical and ultraviolet spectra of most active galactic nuclei. The origin of the optical/UV \feii emission is still a question open to debate. The variability of \feii would give clues to this origin. Using 7.5 yr spectroscopic monitoring data of one Palomer-Green (PG) quasi-stellar object (QSO), PG 1700+518, with strong optical \feii emission, we obtain the light curves of the continuum \lv, \feii, the broad component of \hb, and the narrow component of \hb by the spectral decomposition. Through the interpolation cross-correlation method, we calculate the time lags for light curves of \feii, the total \hb, the broad component of \hb, and the narrow component of \hb with respect to the continuum light curve. We find that the \feii time lag in PG1700+518 is $209^{+100}_{-147}$ days, and the \hb time lag cannot be determined. Assuming that \feii and \hb emission regions follow the virial relation between the time lag and the FWHM for the \hb and \feii emission lines, we can derive that the \hb time lag is $148^{+72}_{-104}$ days. The \hb time lag calculated from the empirical luminosity--size relation is 222 days, which is consistent with our measured \feii time lag. Considering the optical \feii contribution, PG 1700+518 shares the same characteristic on the spectral slope variability as other 15 PG QSOs in our previous work, i.e., harder spectrum during brighter phase.
NGC 2992 is an intermediate Seyfert 1 galaxy showing outflows on kilo parsec scales which might be due either to AGN or starburst activity. We therefore aim at investigating its central region for a putative starburst in the past and its connection to the AGN and the outflows. Observations were performed with the adaptive optics near infrared integral field spectrograph SINFONI on the VLT, complemented by longslit observations with ISAAC on the VLT, as well as N- and Q-band data from the Spitzer archive. The spatial and spectral resolutions of the SINFONI data are 50 pc and 83 km/s, respectively. The field of view of 3" x 3" corresponds to 450 pc x 450 pc. Br_gamma equivalent width and line fluxes from PAHs were compared to stellar population models to constrain the age of the putative recent star formation. A simple geometric model of two mutually inclined disks and an additional cone to describe an outflow was developed to explain the observed complex velocity field in H_2 1-0S(1). The morphologies of the Br_gamma and the stellar continuum are different suggesting that at least part of the Br_gamma emission comes from the AGN. This is confirmed by PAH emission lines at 6.2 micron and 11.2 micron and the strength of the silicon absorption feature at 9.7 micron, which point to dominant AGN activity with a relatively minor starburst contribution. We find a starburst age of 40 Myr - 50 Myr from Br_gamma line diagnostics and the radio continuum; ongoing star formation can be excluded. Both the energetics and the timescales indicate that the outflows are driven by the AGN rather than the starburst. The complex velocity field observed in H_2 1-0S(1) in the central 450 pc can be explained by the superposition of the galaxy rotation and an outflow.
We present the integrated Halpha emission line profile for 157 HII regions in the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the importance of a good characterization of the instrumental response function for the study of line profile shapes. The luminosity-velocity dispersion relation is also studied, and in the log(L)-log(sigma) plane we do not find a linear relation, but an upper envelope with equation log(L)=1.3 *log(sigma)+37.6. For the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity L=10^38.5 ergs, in full agreement with previous studies of other galaxies, reinforcing the idea of using HII regions as standard candles.
Motivated by the fact that cosmological perturbations of inflationary quantum origin were born Gaussian, the search for non-Gaussianities in the cosmic microwave background (CMB) anisotropies is considered as the privileged probe of non-linear physics in the early universe. Cosmic strings are active sources of gravitational perturbations and incessantly produce non-Gaussian distortions in the CMB. Even if, on the currently observed angular scales, they can only contribute a small fraction of the CMB angular power spectrum, cosmic strings could actually be the main source of its non-Gaussianities. In this article, after having reviewed the basic cosmological properties of a string network, we present the signatures Nambu-Goto cosmic strings would induce in various observables ranging from the one-point function of the temperature anisotropies to the bispectrum and trispectrum. It is shown that string imprints are significantly different than those expected from the primordial type of non-Gaussianity and could therefore be easily distinguished.
We present the gamma-ray data of the extraordinary flaring activity above 100 MeV from the flat spectrum radio quasar 3C 454.3 detected by AGILE during the month of December 2009. 3C 454.3, that has been among the most active blazars of the FSRQ type since 2007, was detected in the gamma-ray range with a progressively rising flux since November 10, 2009. The gamma-ray flux reached a value comparable with that of the Vela pulsar on December 2, 2009. Remarkably, between December 2 and 3, 2009 the source more than doubled its gamma-ray emission and became the brightest gamma-ray source in the sky with a peak flux of F_{\gamma,p} = (2000 \pm 400) x 10^-8 ph cm^-2 s^-1 for a 1-day integration above 100 MeV. The gamma-ray intensity decreased in the following days with the source flux remaining at large values near F \simeq (1000 \pm 200) x 10^-8 ph cm^-2 s^-1 for more than a week. This exceptional gamma-ray flare dissipated among the largest ever detected intrinsic radiated power in gamma-rays above 100 MeV (L_{\gamma, source, peak} \simeq 3 x 10^46 erg s^-1, for a relativistic Doppler factor of {\delta} \simeq 30). The total isotropic irradiated energy of the month-long episode in the range 100 MeV - 3 GeV is E_{\gamma,iso} \simeq 10^56 erg. We report the intensity and spectral evolution of the gamma-ray emission across the flaring episode. We briefly discuss the important theoretical implications of our detection.
We describe a survey in the ELAIS N2 region with the VLA at 43.4 GHz, carried out with 1627 independent snapshot observations in D-configuration and covering about 0.5 square degrees. One certain source is detected, a previously-catalogued flat-spectrum QSO at z=2.2. A few (<5) other sources may be present at about the 3sigma level, as determined from positions of source-like deflections coinciding with blue stellar objects, or with sources from lower-frequency surveys. Independently we show how all the source-like detections identified in the data can be used with a maximum-likelihood technique to constrain the 43-GHz source counts at a level of ~7 mJy. Previous estimates of the counts at 43 GHz, based on lower-frequency counts and spectral measurements, are consistent with these constraints, although the present results are suggestive of somewhat higher surface densities at the 7 mJy level. They do not provide direct evidence of intrusion of a previously unknown source population, although the several candidate sources need examination before such a population can be ruled out.
We investigate the role of host galaxy classification and black hole mass in a heterogeneous sample of 276 mostly nearby (z<0.1) X-ray and IR selected AGN. Around 90% of Seyfert 1 AGN in bulge-dominated host galaxies (without disk contamination) span a very narrow range in the observed 12um to 2-10keV luminosity ratio (1<R_{IR/X}<7). This narrow dispersion incorporates all possible variations among AGN central engines, including accretion mechanism and efficiency, disk opening angle, orientation to sightline, covering fraction of absorbing material, patchiness of X-ray corona and measured variability. As a result, all models of X-ray and IR production in AGN are very strongly constrained. Among Seyfert 1 AGN, median X-ray and IR luminosities increase with black hole mass at >99% confidence. Using ring morphology of the host galaxy as a proxy for lack of tidal interaction, we find that AGN luminosity in host galaxies within 70Mpc is independent of host galaxy interaction for $\sim$ Gyrs, suggesting that the timescale of AGN activity due to secular evolution is much shorter than that due to tidal interactions. We find that LINER hosts have lower 12um luminosity than the median 12um luminosity of normal disk- and bulge-dominated galaxies which may represent observational evidence for past epochs of feedback that supressed star formation in LINER host galaxies. We propose that nuclear ULXs may account for the X-ray emission from LINER 2s without flat-spectrum, compact radio cores. We confirmed the robustness of our results in X-rays by comparing them with the 14-195keV 22-month BAT survey of AGN, which is all-sky and unbiased by photoelectric absorption.
We consider a neutrino oscillation interpretation of the MiniBooNE low-energy anomaly and the Gallium radioactive source experiments anomaly in the framework of 3+1 four-neutrino mixing schemes. The combined fit of MiniBooNE and Gallium data indicate a possible short-baseline electron neutrino disappearance generated by effective oscillation parameters Delta m^2 >~ 1 eV^2 and 0.06 <~ \sin^2 2 theta <~ 0.6. Considering also the data of the Bugey and Chooz reactor neutrino oscillation experiments and the results of the Mainz and Troitsk Tritium beta-decay experiments, the allowed range of the effective mixing angle is shifted to 0.01 <~ \sin^2 2 theta <~ 0.1. Assuming a hierarchy of masses m_1, m_2, m_3 much smaller than m_4, the predicted contributions of m_4 to the effective neutrino masses in beta-decay and neutrinoless double-beta-decay are, respectively, between about 0.09 and 0.3 eV and between about 0.006 and 0.04 eV.
We study the spectrum of high frequency radiation emerging from mildly dissipative photospheres of long-duration gamma-ray burst outflows. Building on the results of recent numerical investigations, we assume that electrons are heated impulsively to mildly relativistic energies by either shocks or magnetic dissipation at Thomson optical depths of several and subsequently cool by inverse Compton, scattering off the thermal photons of the photosphere. We show that even in the absence of magnetic field and non-thermal leptons, inverse Compton scattering produces power-law tails that extend from the peak of the thermal radiation, at several hundred keV, to several tens of MeV, and possibly up to GeV energies. The slope of the high-frequency power-law is predicted to vary substantially during a single burst, and the model can easily account for the diversity of high-frequency spectra observed by BATSE. Our model works in baryonic as well as in magnetically dominated outflows, as long as the magnetic field component is not overwhelmingly dominant.
Since the Aharonov-Bohm effect is the purely quantum effect that has no analogues in classical physics, its persistence in the quasiclassical limit seems to be hardly possible. Nevertheless, we show that the scattering Aharonov-Bohm effect does persist in the quasiclassical limit owing to the diffraction, i.e. the Fraunhofer diffraction in the case when space outside the enclosed magnetic flux is Euclidean, and the Fresnel diffraction in the case when the outer space is conical. Hence, the enclosed magnetic flux can serve as a gate for the propagation of short-wavelength, almost classical, particles. In the case of conical space, this quasiclassical effect which is in principle detectable depends on the particle spin.
Inflationary scenarios in string theory often involve a large number of light scalar fields, whose presence can enrich the post-inflationary evolution of primordial fluctuations generated during the inflationary epoch. We provide a simple example of such post-inflationary processing within an explicit string-inflationary construction, using a Kahler modulus as the inflaton within the framework of LARGE Volume Type-IIB string flux compactifications. We argue that inflationary models within this broad category often have a selection of scalars that are light enough to be cosmologically relevant, whose contributions to the primordial fluctuation spectrum can compete with those generated in the standard way by the inflaton. These models consequently often predict nongaussianity at a level, f_NL ~ O(10), potentially observable by the Planck satellite, with a bi-spectrum maximized by triangles with squeezed shape in a string realisation of the curvaton scenario. We argue that the observation of such a signal would robustly prefer string cosmologies such as these that predict a multi-field dynamics during the very early universe.
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As deeper observations discover increasingly distant galaxies, characterizing the properties of high-redshift galaxy populations will become increasingly challenging and paramount. We present a method for measuring the clustering bias of high-redshift galaxies from the field-to-field scatter in their number densities induced by cosmic variance. Multiple widely-separated fields are observed to provide a large number of statistically-independent samples of the high-redshift galaxy population. The expected Poisson uncertainty is removed from the measured dispersion in the distribution of galaxy number counts observed across these many fields, leaving, on average, only the contribution to the scatter expected from cosmic variance. With knowledge of the Lambda Cold Dark Matter power spectrum, the galaxy bias is then calculated from the measured cosmic variance. The results of cosmological N-body simulations can then be used to estimate the halo mass associated with the measured bias. We use Monte Carlo simulations to demonstrate that Hubble Space Telescope pure parallel programs will be able to determine galaxy bias at z>~6 using this method, complementing future measurements from correlation functions.
Although rapid reorientation of a black hole spin axis (lasting less than a few Myr) has been suggested as a mechanism for the formation of wings in X-shaped radio galaxies (XRGs), to date no convincing case of reorientation has been found in any XRG. Alternative wing formation models such as the hydrodynamic backflow models are supported by observed trends indicating that XRGs form preferentially with jets aligned along the major axis of the surrounding medium and wings along the minor axis. In this Letter, we present a deep Chandra observation of 4C +00.58, an oddball XRG with its jet oriented along the minor axis. By using the X-ray data in tandem with available radio and optical data, we estimate relevant timescales with which to evaluate wing formation models. The hydrodynamic models have difficulty explaining the long wings, whereas the presence of X-ray cavities (suggesting jet activity along a prior axis) and a potential stellar shell (indicating a recent merger) favor a merger-induced reorientation model.
We use weak lensing data from the Hubble Space Telescope COSMOS survey to measure the second- and third-moments of the cosmic shear field, estimated from about 450,000 galaxies with average redshift <z> ~ 1.3. We measure two- and three-point shear statistics using a tree-code, dividing the signal in E, B and mixed components. We present a detection of the third-order moment of the aperture mass statistic and verify that the measurement is robust against systematic errors caused by point spread function (PSF) residuals and by the intrinsic alignments between galaxies. The amplitude of the measured three-point cosmic shear signal is in very good agreement with the predictions for a WMAP7 best-fit model, whereas the amplitudes of potential systematics are consistent with zero. We make use of three sets of large Lambda CDM simulations to test the accuracy of the cosmological predictions and to estimate the influence of the cosmology-dependent covariance. We perform a likelihood analysis using the measurement and find that the Omega_m-sigma_8 degeneracy direction is well fitted by the relation: sigma_8 (Omega_m/0.30)^(0.49)=0.78+0.11/-0.26. We present the first measurement of a more generalised three-point shear statistic and find a very good agreement with the WMAP7 best-fit cosmology. The cosmological interpretation of this measurement gives sigma_8 (Omega_m/0.30)^(0.46)=0.69 +0.08/-0.14. Furthermore, the combined likelihood analysis of this measurement with the measurement of the second order moment of the aperture mass improves the accuracy of the cosmological constraints, showing the high potential of this combination of measurements to infer cosmological constraints.
A sample consisting of 27 X-ray selected galaxy clusters from the XMM-LSS survey is used to study the evolution in the X-ray surface brightness profiles of the hot intracluster plasma. These systems are mostly groups and poor clusters, with temperatures 0.6-4.8 keV, spanning the redshift range 0.05 to 1.05. Comparing the profiles with a standard beta-model motivated by studies of low redshift groups, we find 54% of our systems to possess a central excess, which we identify with a cuspy cool core. Fitting beta-model profiles, allowing for blurring by the XMM point spread function, we investigate trends with both temperature and redshift in the outer slope (beta) of the X-ray surface brightness, and in the incidence of cuspy cores. Fits to individual cluster profiles and to profiles stacked in bands of redshift and temperature indicate that the incidence of cuspy cores does not decline at high redshifts, as has been reported in rich clusters. Rather such cores become more prominent with increasing redshift. Beta shows a positive correlation with both redshift and temperature. Given the beta-T trend seen in local systems, we assume that temperature is the primary driver for this trend. Our results then demonstrate that this correlation is still present at z~0.3, where most of our clusters reside.
Recent observational results found a bend in the Tully-Fisher Relation in such a way that low mass systems lay below the linear relation described by more massive galaxies. We intend to investigate the origin of the observed features in the stellar and baryonic Tully-Fisher relations and analyse the role played by galactic outflows on their determination. Cosmological hydrodynamical simulations which include Supernova feedback were performed in order to follow the dynamical evolution of galaxies. We found that Supernova feedback is a fundamental process in order to reproduce the observed trends in the stellar Tully-Fisher relation. Simulated slow rotating systems tend to have lower stellar masses than those predicted by the linear fit to the massive end of the relation, consistently with observations. This feature is not present if Supernova feedback is turned off. In the case of the baryonic Tully-Fisher relation, we also detect a weaker tendency for smaller systems to lie below the linear relation described by larger ones. This behaviour arises as a result of the more efficient action of Supernovae in the regulation of the star formation process and in the triggering of powerful galactic outflows in shallower potential wells which may heat up and/or expel part of the gas reservoir.
We report the detection of the CO J=1-0 emission line in three near-infrared selected star-forming galaxies at z~1.5 with the Very Large Array (VLA) and the Green Bank telescope (GBT). These observations directly trace the bulk of molecular gas in these galaxies. We find H_2 gas masses of 8.3 \pm 1.9 x 10^{10} M_sun, 5.6 \pm 1.4 x 10^{10} M_sun and 1.23 \pm 0.34 x 10^{11} M_sun for BzK-4171, BzK-21000 and BzK-16000, respectively, assuming a conversion alpha_CO=3.6 M_sun (K km s^{-1} pc^{2})^{-1}. We combined our observations with previous CO 2-1 detections of these galaxies to study the properties of their molecular gas. We find brightness temperature ratios between the CO 2-1 and CO 1-0 emission lines of 0.80_{-0.22}^{+0.35}, 1.22_{-0.36}^{+0.61} and 0.41_{-0.13}^{+0.23} for BzK-4171, BzK-21000 and BzK-16000, respectively. At the depth of our observations it is not possible to discern between thermodynamic equilibrium or sub-thermal excitation of the molecular gas at J=2. However, the low temperature ratio found for BzK-16000 suggests sub-thermal excitation of CO already at J=2. For BzK-21000, a Large Velocity Gradient model of its CO emission confirms previous results of the low-excitation of the molecular gas at J=3. From a stacked map of the CO 1-0 images, we measure a CO 2-1 to CO 1-0 brightness temperature ratio of 0.92_{-0.19}^{+0.28}. This suggests that, on average, the gas in these galaxies is thermalized up to J=2, has star-formation efficiencies of ~100 L_sun (K km s^{-1} pc^2)^{-1} and gas consumption timescales of ~0.4 Gyr, unlike SMGs and QSOs at high redshifts.
We present the clustering measurement of hard X-ray selected AGN in the local Universe. We used a sample of 199 sources spectroscopically confirmed detected by Swift-BAT in its 15-55 keV all-sky survey. We measured the real space projected auto-correlation function and detected a signal significant on projected scales lower than 200 Mpc/h. We measured a correlation length of r0=5.56+0.49-0.43 Mpc/h and a slope {\gamma}=1.64-0.08 -0.07. We also measured the auto-correlation function of Type I and Type II AGN and found higher correlation length for Type I AGN. We have a marginal evidence of luminosity dependent clustering of AGN, as we detected a larger correlation length of luminous AGN than that of low luminosity sources. The corresponding typical host DM halo masses of Swift-BAT are log(MDMH) 12-14 h^-1 M/M_sun, depending on the subsample. For the whole sample we measured log(MDMH)\sim 13.15 h-1 M/M_sun which is the typical mass of a galaxy group. We estimated that the local AGN population has a typical lifetime tau_AGN \sim 0.7 Gyr, it is powered by SMBH with mass MBH \sim 1-10x10^8 M_\odot and accreting with very low efficiency, log(epsilon)-2.0. We also conclude that local AGN host galaxies are typically red-massive galaxies with stellar mass of the order 2-80x10^10 h^-1 M_sun. We compared our results with clustering predictions of merger-driven AGN triggering models and found a good agreement.
We attempt in this paper to check the consistency of the observed Stellar Mass Function (SMF), SFR functions and the cosmic star formation rate density with simple backward evolutionary models. Starting from observed SMF for star-forming galaxies, we use backwards models to predict the evolution of a number of quantities, such as the SFR function, the cosmic SFR density and the Velocity Function. The velocity being a parameter attached to a galaxy during its history (contrary to the stellar mass), this approach allows us to quantify the number density evolution of galaxies of a given velocity, e.g. of the Milky Way siblings. Observations suggest that the SMF of star forming galaxies is constant between redshift 0 and 1. In order to reproduce this result, we must quench star formation in a number of star forming galaxies. The SMF of these quenched galaxies is consistent with available data concerning the increase in the population of quiescent galaxies in the same redshift interval. The SMF of quiescent galaxies is then mainly determined by the distribution of active galaxies that must stop star formation, with a modest mass redistribution during mergers. The cosmic SFR density, and the evolution of the SFR functions are relatively well recovered, although they provide some clue for a small evolution of the SMF of star forming galaxies at the lowest redshifts. We thus consider that we have obtained in a simple way a relatively consistent picture of the evolution of galaxies at intermediate redshifts. We note that if this picture is correct, 50 percent of the Milky-Way sisters (galaxies with the same velocity as our Galaxy, i.e. 220 km/s) have quenched their star formation since redshift 1 (and an even larger fraction for larger velocities). We discuss the processes that might be responsible for this transformation.
We present Herschel far-infrared (FIR) observations of two sub-mm bright quasars at high redshift: SDSS J1148+5251 (z=6.42) and BR 1202-0725 (z=4.69) obtained with the PACS instrument. Both objects are detected in the PACS photometric bands. The Herschel measurements provide additional data points that constrain the FIR spectral energy distributions (SEDs) of both sources, and they emphasise a broad range of dust temperatures in these objects. For lambda_rest ~< 20mu, the two SEDs are very similar to the average SEDs of quasars at low redshift. In the FIR, however, both quasars show excess emission compared to low-z QSO templates, most likely from cold dust powered by vigorous star formation in the QSO host galaxies. For SDSS J1148+5251 we detect another object at 160mu with a distance of ~10 arcseconds from the QSO. Although no physical connection between the quasar and this object can be shown with the available data, it could potentially confuse low-resolution measurements, thus resulting in an overestimate of the FIR luminosity of the z=6.42 quasar.
The redshifts and luminosities of Type 1A supernovae are conventionally fitted with the current paradigm, which holds that the galaxies are locally stationary in an expanding metric. The fit fails unless the expansion is accelerating; driven perhaps by "dark energy". Is the recession of the galaxies slowed down by gravity or speeded up by some repulsive force? To shed light on this question the redshifts and apparent magnitudes of type 1A supernovae are re-analysed in a cartesian frame of reference omitting gravitational effects. The redshift is ascribed to the relativistic Doppler effect which gives the recession velocity when the light was emitted; if this has not changed, the distance reached and the luminosity follow immediately. This simple concept fits the observations surprisingly well. It appears that the galaxies recede at unchanging velocities, so on the largest scale there is no significant intergalactic force. Reasons for the apparent absence of an intergalactic force are discussed.
As so far, the higher redshift of Gamma-ray bursts (GRBs) can extend to $z\sim 8.1$ which makes it as complementary probe of dark energy to supernova Ia. However, the calibration of GRBs is still a big challenge when they are used to constrain cosmological models. Though, the absolute magnitude of GRBs is not known, the slopes of GRBs correlations can be used as a useful constraint to dark energy in a completely cosmological model in-denpendent way. In this paper, we follow Wang's model-independent distance measurement method and calculate their values by using $109$ GRBs events via the so-called Amati's relation. Then, these distances are used to constrain $\Lambda$CDM model.
The CMB maps obtained by observations always possess domains which have to be masked due to severe uncertainties with respect to the genuine CMB signal. Cosmological analyses ideally use full CMB maps in order to get e.g. the angular power spectrum. There are attempts to reconstruct the masked regions at least at low resolutions, i.e. at large angular scales, before a further analysis follows. In this paper, the quality of the reconstruction is investigated for the ILC (7yr) map as well as for 1000 CMB simulations of the LambdaCDM concordance model. The latter allows an error estimation for the reconstruction algorithm which reveals some drawbacks. The analysis points to errors of the order of a significant fraction of the mean temperature fluctuation of the CMB. The temperature 2-point correlation function C(theta) is evaluated for different reconstructed sky maps which leads to the conclusion that it is safest to compute it on the cut-sky.
We measure the rest-frame colors (dust-corrected), infrared luminosities, star formation rates, and stellar masses of 92 galaxies in a Spitzer-selected cluster at z=1.62. By fitting spectral energy distributions to 10-band photometry (0.4 micron < lambda(obs) < 8 micron) and measuring 24 micron fluxes for the 12 spectroscopically confirmed and 80 photometrically selected members, we discover an exceptionally high level of star formation in the cluster core of ~1700 Msun/yr per Mpc^2. The cluster galaxies define a strong blue sequence in (U-V) color and span a range in color. We identify 17 members with L(IR)>10^(11) Lsun, and these IR luminous members follow the same trend of increasing star formation with stellar mass that is observed in the field at z~2. Using rates derived from both the 24 micron imaging and SED fitting, we find that the relative fraction of star-forming members triples from the lowest to highest galaxy density regions, e.g. the IR luminous fraction increases from ~8% at Sigma~10 gal per Mpc^2 to ~25% at Sigma>100 gal per Mpc^2. The observed increase is a reversal of the well-documented trend at z<1 and signals that we have finally reached the epoch when massive cluster galaxies are still forming a substantial fraction of their stars.
The new release of data from Wilkinson Microwave Anisotropy Probe improves the observational situation with relic gravitational waves. The 7-year results enhance the indications of relic gravitational waves in the existing data and change to the better the prospects of confident detection of relic gravitational waves by the currently operating Planck satellite. We apply to WMAP7 data the same methods of analysis that we used earlier [W. Zhao, D. Baskaran, and L.P. Grishchuk, Phys. Rev. D 80, 083005 (2009)] with WMAP5 data. The maximum likelihood value of the quadrupole ratio $R$, which characterizes the amount of relic gravitational waves, increases up to R=0.264, and the interval separating this value from the point R=0 (the hypothesis of no gravitational waves) increases up to a $2\sigma$ level. Assuming that the WMAP7 maximum likelihood set of parameters is correct, the signal-to-noise ratio $S/N$ for the detection of relic gravitational waves by the Planck experiment increases up to $S/N=4.04$, even under pessimistic assumptions with regard to residual foreground contamination and instrumental noises. We comment on theoretical frameworks that, in the case of success, will be accepted or decisively rejected by the Planck observations.
The understanding of the origin of dark matter has great importance for cosmology and particle physics. Several interesting extensions of the standard model dealing with solution of this problem motivate the concept of hidden sectors consisting of SU(3)xSU(2)_LxU(1)_Y singlet fields. Among these models, the mirror matter model is certainly one of the most interesting. The model explains the origin of parity violation in weak interactions, it could also explain the baryon asymmetry of the Universe and provide a natural ground for the explanation of dark matter. The mirror matter could have a portal to our world through photon-mirror photon mixing (epsilon). This mixing would lead to orthopositronium (o-Ps) to mirror orthopositronium oscillations, the experimental signature of which is the apparently invisible decay of o-Ps. In this paper, we describe an experiment to search for the decay o-Ps -> invisible in vacuum by using a pulsed slow positron beam and a massive 4pi BGO crystal calorimeter. The developed high efficiency positron tagging system, the low calorimeter energy threshold and high hermiticity allow the expected sensitivity in mixing strength to be epsilon about 10^-9, which is more than one order of magnitude below the current Big Bang Nucleosynthesis limit and in a region of parameter space of great theoretical and phenomenological interest. The vacuum experiment with such sensitivity is particularly timely in light of the recent DAMA/LIBRA observations of the annual modulation signal consistent with a mirror type dark matter interpretation.
Nearly all globular clusters (GCs) studied to date show evidence for multiple stellar populations, in stark contrast to the conventional view that GCs are a mono-metallic, coeval population of stars. This generic feature must therefore emerge naturally within massive star cluster formation. Building on earlier work, we propose a simple physical model for the early evolution (several 10^8 yr) of GCs that is consistent with all of the available data. In our model, type II SNe from a first generation of star formation clears the GC of its initial gas reservoir. Over the next several 10^8 yr, mass lost from AGB stars and matter accreted from the ambient ISM collect at the center of the GC; this material must remain quite cool (T~100K), but does not catastrophically cool on a crossing time because of the high Lyman-Werner flux density in young GCs. The collection of gas within the GC must compete with ram pressure stripping from the ambient ISM. After several 10^8 yr, the Lyman-Werner photon flux density drops by more than three orders of magnitude, allowing molecular hydrogen and then stars to form. After this second generation of star formation, type II SNe from the second generation and then prompt type Ia SNe associated with the first generation maintain a gas-free GC, thereby ending the cycle of star formation events. Our model makes clear predictions for the presence or absence of multiple stellar populations within GCs as a function of GC mass and environment. Analyzing intermediate-age LMC clusters, we find for the first time evidence for a mass threshold of ~10^4Msun below which LMC clusters appear to be truly coeval. This threshold mass is consistent with our predictions for the mass at which ram pressure stripping is capable of clearing gas from clusters in the LMC at the present epoch. (ABRIDGED)
We report SMARTS and Gemini observations of the optical transient (OT) associated with gamma-ray burst (GRB) 091127, at redshift 0.49, taken between 1.8 hr and 102 days following the Swift trigger. In our early-time observations, the OT fades in a manner consistent with previously observed GRB afterglows. However, after 9 days post-burst, the OT is observed to brighten for a period of ~2 weeks, after which the source resumes fading. A comparison of this late-time "bump" to SN 1998bw (the broad-lined Type Ic supernova associated with GRB 980425), and several other GRB supernovae (SNe), indicates that the most straightforward explanation is that GRB 091127 was accompanied by a contemporaneous SN (SN 2009nz) that peaked at a magnitude of M_V=-19.0+/-0.2. SN 2009nz is globally similar to other GRB supernovae, but evolves slightly faster than SN 1998bw and reaches a slightly dimmer peak magnitude. We also analyze the early-time UV-optical-IR spectral energy distribution of the afterglow of GRB 091127 and find that there is little to no reddening in the host galaxy along the line-of-slight to this burst.
Excitation of multicomponent dark matter in the galactic center has been proposed as the source of low-energy positrons that produce the excess 511 keV gamma rays that have been observed by INTEGRAL. Such models have also been promoted to explain excess high-energy electrons/positrons observed by the PAMELA, Fermi/LAT and H.E.S.S. experiments. We investigate whether one model can simultaneously fit all three anomalies, in addition to further constraints from inverse Compton scattering by the high-energy leptons. We find models that fit both the 511 keV and PAMELA excesses at dark matter masses M < 400 GeV, but not the Fermi lepton excess. The conflict arises because a more cuspy DM halo profile is needed to match the observed 511 keV signal than is compatible with inverse Compton constraints at larger DM masses.
A method for the search of exact solutions for equation of a nonlocal scalar field in nonflat metric is considered. In the Friedmann-Robertson-Walker metric the proposed method can be used in the case of an arbitrary potential, with the exception of linear and quadratic potentials, and allows to get in quadratures solutions, which depend on two arbitrary parameters. Exact solutions have been found for an arbitrary cubic potential, which consideration is motivated by the string field theory, as well as for exponential, logarithmic and power potentials.
Here we show that in the case when double peaked emission lines originate from outer parts of accretion disk, their variability could be caused by perturbations in the disk emissivity. In order to test this hypothesis, we introduced a model of disk perturbing region in the form of a single bright spot (or flare) by a modification of the power law disk emissivity in appropriate way. The disk emission was then analyzed using numerical simulations based on ray-tracing method in Kerr metric and the corresponding simulated line profiles were obtained. We applied this model to the observed H-beta line profiles of 3C 390.3 (observed in the period 1995-1999), and estimated the parameters of both, accretion disk and perturbing region. Our results show that two large amplitude outbursts of the H-beta line observed in 3C 390.3 could be explained by successive occurrences of two bright spots on approaching side of the disk. These bright spots are either moving, originating in the inner regions of the disk and spiralling outwards by crossing small distances during the period of several years, or stationary. In both cases, their widths increase with time, indicating that they most likely decay.
We point out some of the outstanding challenges for embedding inflationary cosmology within string theory studying the process of reheating for models where the inflaton is a closed string mode parameterising the size of an internal cycle of the compactification manifold. A realistic model of inflation must explain the tiny perturbations in the cosmic microwave background radiation and also how to excite the ordinary matter degrees of freedom after inflation, required for the success of Big Bang Nucleosynthesis. We study these issues focusing on two promising inflationary models embedded in LARGE volume type IIB flux compactifications. We show that phenomenological requirements and consistency of the effective field theory treatment imply the presence at low energies of a hidden sector together with a visible sector, where the Minimal Supersymmetric Standard Model fields are residing. A detailed calculation of the inflaton coupling to the fields of the hidden sector, visible sector, and moduli sector, reveals that the inflaton fails to excite primarily the visible sector fields, instead hidden sector fields are excited copiously after the end of inflation. This sets severe constraints on hidden sector model building where the most promising scenario emerges as a pure N=1 SYM theory, forbidding the kinematical decay of the inflaton to the hidden sector. In this case it is possible to reheat the Universe with the visible degrees of freedom even though in some cases we discover a new tension between TeV scale SUSY and reheating on top of the well-known tension between TeV scale SUSY and inflation.
In this report we construct a phenomenological model in which the time variation of the fine structure constant, $\alpha$, is induced by a parity and charge-parity (PCP) violating interaction. Such a PCP violation in the photon sector has a distinct physical origin from that in the conventional models of this kind. We calculate the cosmological birefringence so induced in our model and show that it in turn produces a new non-vanishing multipole moment correlation between the temperature and the polarization anisotropies in the CMB spectrum. We have also calculated the effect of our new PCP violating term on the variation of $\alpha$ during the cosmic evolution. We found that only in the radiation dominated era can the contribution of the new PCP violating term to the variation of $\alpha$ be non-vanishing.
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