3] arXiv:0802.4094 [ps, pdf, other] Title: Confirmation of the remarkable compactness of massive quiescent galaxies at z~2.3: early-type galaxies did not form in a simple monolithic collapse Authors: Pieter van Dokkum, Marijn Franx, Mariska Kriek, Bradford Holden, Garth Illingworth, Daniel Magee, Rychard Bouwens, Danilo Marchesini, Ryan Quadri, Greg Rudnick, Edward Taylor, Sune Toft Comments: Accepted for publication in ApJ Letters License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) Using deep near-infrared spectroscopy Kriek et al. (2006) found that ~45% of massive galaxies at z~2.3 have evolved stellar populations and little or no ongoing star formation. Here we determine the sizes of these quiescent galaxies using deep, high-resolution images obtained with HST/NIC2 and laser guide star-assisted Keck/AO. Considering that their median stellar mass is 1.7x10^11 Solar masses the galaxies are remarkably small, with a median effective radius of 0.9 kpc. Galaxies of similar mass in the nearby Universe have sizes of ~5 kpc and average stellar densities which are two orders of magnitude lower than the z~2.3 galaxies. These results extend earlier work at z~1.5 and confirm previous studies at z>2 which lacked spectroscopic redshifts and imaging of sufficient resolution to resolve the galaxies. Our findings demonstrate that fully assembled early-type galaxies make up at most ~10% of the population of K-selected quiescent galaxies at z~2.3, effectively ruling out simple monolithic models for their formation. The galaxies must evolve significantly after z~2.3, through dry mergers or other processes, consistent with predictions from hierarchical models. [6] arXiv:0802.4105 [ps, pdf, other] Title: The Star Formation History of the Universe as Revealed by Deep Radio Observations Authors: N. Seymour (1), T. Dwelly (2), D. Moss (2), I. McHardy (2), A. Zoghbi (2,3), G. Rieke (4), M. Page (5), A. Hopkins (6), N. Loaring (7) ((1) Spitzer Science Center, (2) University of Southampton, (3) IoA, University of Cambridge, (4) Steward Observatory, (5) Mullard Space Science Laboratory, (6) University of Sydney, (7) SALT) Comments: 15 pages, 10 figures, MNRAS, in press, Figure A1 included as gif to save space, paper with full resolution figure available here: this http URL License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) Discerning the exact nature of the sub-mJy radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep ground based optical follow-up and observations from the Spitzer Space Telescope we are able to disentangle the radio-selected Active Galactic Nuclei (AGN) and Star Forming Galaxy (SFG) populations for the first time in a deep multi-frequency VLA/MERLIN Survey of the 13^H XMM-Newton/Chandra Deep Field. The discrimination diagnostics include radio morphology, radio spectral index, radio/near-IR and mid-IR/radio flux density ratios. We are now able to calculate the extragalactic Euclidean normalised source counts separately for AGN and SFGs. We find that while SFGs dominate at the faintest flux densities and account for the majority of the up-turn in the counts, AGN still make up around one quarter of the counts at ~5 uJy (1.4 GHz). Using radio luminosity as an unobscured star formation rate (SFR) measure we are then able to examine the comoving SFR density of the Universe up to z=3 which agrees well with measures at other wavelengths. We find a rough correlation of SFR with stellar mass for both the sample presented here and a sample of local radio-selected SFGs from the 6df-NVSS survey. This work also confirms the existence of, and provides alternative evidence for, the evolution of distribution of star formation by galaxy mass: ``downsizing''. As both these samples are SFR-selected, this result suggests that there is a maximum SFR for a given galaxy that depends linearly on its stellar mass. The low ``characteristic times'' (inverse specific SFR) of the SFGs in our sample are similar to those of the 6dF-NVSS sample, implying that most of these sources are in a current phase of enhanced star formation. [19] arXiv:0802.4154 [ps, pdf, other] Title: Supernovae and Cosmology Authors: Bruno Leibundgut Comments: Published in General Relativity and Gravitation, 40, 221 Journal-ref: Gen Relativ Gravit (2008) 40, 221 License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) The extreme luminosity and their fairly unique temporal behaviour have made supernovae a superb tool to measure distances in the universe. As complex astrophysical events they provide interesting insights into explosion physics, explosive nucleosynthesis, hydrodynamics of the explosion and radiation transport. They are an end product of stellar evolution and provide clues to the stellar composition. Since they can be observed at large distances they have become critical probes to further explore astrophysical effects, like dust properties in external galaxies and the star formation history of galaxies. Some of the astrophysics interferes with the cosmological applications of supernovae. The local velocity field, distorted by the gravitational attraction of the local large scale structure, and the reddening law appear at the moment the major limitations in the accuracy with which cosmological parameters can be determined. These absorption effects can introduce a secondary bias into the observations of the distant supernovae, which needs to be carefully evaluated. Supernovae have been used for the measurement of the Hubble constant, i.e. the current expansion rate of the universe, and the accelerated cosmic expansion directly inferred from the apparent faintness of the distant supernovae. 1] arXiv:0802.4288 [ps, pdf, other] Title: The 2dF-SDSS LRG and QSO survey: Evolution of the clustering of Luminous Red Galaxies since z = 0.6 Authors: David A. Wake, Ravi K. Sheth, Robert C. Nichol, Carlton M. Baugh, Joss Bland-Hawthorn, Russell Cannon, Matthew Colless, Warrick J. Couch, Scott M. Croom, Roberto De Propris, Michael J. Drinkwater, Alastair C. Edge, Jon Loveday, Tsz Yan Lam, Kevin A. Pimbblet, Isaac G. Roseboom, Nicholas P. Ross, Donald P. Schneider, Tom Shanks, Robert G. Sharp Comments: 19 pages, submitted to MNRAS License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) We present an analysis of the small-to-intermediate scale clustering of samples of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey and the 2dF-SDSS LRG and QSO (2SLAQ) survey carefully matched to have the same rest-frame colours and luminosity. We study the spatial two-point auto-correlation function in both redshift-space and real-space of a combined sample of over 10,000 LRGs, which represent the most massive galaxies in the universe with stellar masses > 10^11 h^-1 M_sun and space densities 10^-4 h^-3 Mpc^-3. We find no significant evolution in the amplitude r_0 of the correlation function with redshift, but do see a slight decrease in the slope with increasing redshift over 0.19 < z < 0.55 and scales of 0.32 < r < 32 h^-1 Mpc. We compare our measurements with the predicted evolution of dark matter clustering and use the halo model to interpret our results. We find that our clustering measurements are inconsistent (>99.9% significance) with a passive model whereby the LRGs do not merge with one another; a model with a merger rate of 7.5 +/- 2.3% from z = 0.55 to z = 0.19 (i.e. an average rate of 2.4% Gyr^-1) provides a better fit to our observations. Our clustering and number density measurements are consistent with the hypothesis that the merged LRGs were originally central galaxies in different haloes which, following the merger of these haloes, merged to create a single Brightest Cluster Galaxy. In addition, we show that the small-scale clustering signal constrains the scatter in halo merger histories, and argue that the present data suggests that this scatter is sub-Poisson. While this is a generic prediction of hierarchical models, it has not been tested before. [9] arXiv:0803.0063 [ps, pdf, other] Title: Unresolved emission and ionized gas in the bulge of M31 Authors: A. Bogdan (MPA), M. Gilfanov (MPA, IKI) Comments: 10 pages, submitted to MNRAS License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) We study the origin of unresolved X-ray emission from the bulge of M31 based on archival Chandra and XMM-Newton observations. We demonstrate that three different components are present: (i) Broad-band emission from a large number of faint sources -- mainly accreting white dwarfs and active binaries, associated with the old stellar population, similar to the Galactic Ridge X-ray emission of the Milky Way. The X-ray to K-band luminosity ratios are compatible with those for the Milky Way and for M32, in the 2 - 10 keV band it is (3.6 +/- 0.2) x 10^27 erg/s/L_sun. (ii) Soft emission from ionized gas with temperature of about ~ 300 eV and mass of ~ 2 x 10^6 M_sun. The gas distribution is significantly extended along the minor axis of the galaxy suggesting that it may be outflowing in the direction perpendicular to the galactic disk. The mass and energy supply from evolved stars and type Ia supernovae is sufficient to sustain the outflow. We also detect a shadow cast on the gas emission by spiral arms and the 10-kpc star-forming ring, confirming significant extent of the gas in the ``vertical'' direction. (iii) Hard extended emission from spiral arms, most likely associated with young stellar objects and young stars located in the star-forming regions. The L_X/SFR ratio equals ~ 7.5 x 10^38 (erg/s)/(M_sun/yr) which is about ~ 1/3 of the HMXBs contribution, determined earlier from Chandra observations of other nearby galaxies. [15] arXiv:0803.0109 [ps, pdf, other] Title: Cold gas accretion in galaxies Authors: R. Sancisi, F. Fraternali, T. Oosterloo, J. M. van der Hulst Comments: To appear in Astronomy & Astrophysics Reviews. 34 pages. Full-resolution version available at this http URL License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: 1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. It may be regarded as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material infall as the stellar streams observed in the halos of our galaxy and M31. 2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is produced by galactic fountains, it is likely that a part of it is of extragalactic origin. 3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed as the origin. 4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean ``visible'' accretion rate of cold gas in galaxies of at least 0.2 Msol/yr. In order to reach the accretion rates needed to sustain the observed star formation (~1 Msol/yr), additional infall of large amounts of gas from the IGM seems to be required. 19] arXiv:0803.0147 [pdf, other] Title: Numerical Simulations Unravel the Cosmic Web Authors: C.-A. Faucher-Giguere, A. Lidz, L. Hernquist (Harvard University) Comments: 10 pages, 2 figures. Appeared as a solicited Perspective article in the January 4, 2008 special issue of Science on the cosmic web License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) The universe is permeated by a network of filaments, sheets, and knots collectively forming a "cosmic web.'' The discovery of the cosmic web, especially through its signature of absorption of light from distant sources by neutral hydrogen in the intergalactic medium, exemplifies the interplay between theory and experiment that drives science, and is one of the great examples in which numerical simulations have played a key and decisive role. We recount the milestones in our understanding of cosmic structure, summarize its impact on astronomy, cosmology, and physics, and look ahead by outlining the challenges faced as we prepare to probe the cosmic web at new wavelengths. 21] arXiv:0803.0161 [ps, pdf, other] Title: Galaxy Pairs in the Sloan Digital Sky Survey I: Star Formation, AGN Fraction, and the Luminosity/Mass-Metallicity Relation Authors: Sara L. Ellison, David R. Patton, Luc Simard, Alan W. McConnachie Comments: Accepted for publication in the Astronomical Journal License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) (Abridged). We present a sample of 1716 galaxies with companions within Delta v < 500 km/s, r_p < 80 kpc and stellar mass ratio 0.1 < M_1/M_2 < 10 from the Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4). In agreement with previous studies, we find an enhancement in the star formation rate (SFR) of galaxy pairs at projected separations < 30--40 kpc. In addition, we find that this enhancement is highest (and extends to the greatest separations) for galaxies of approximately equal mass, the so-called `major' pairs. However, SFR enhancement can still be detected for a sample of galaxy pairs whose masses are within a factor of 10 of each other. In agreement with the one previous study of the luminosity-metallicity (LZ) relation in paired galaxies, we find an offset to lower metallicities (by ~ 0.1 dex) for a given luminosity for galaxies in pairs compared to the control sample. We also present the first mass-metallicity (MZ) relation comparison between paired galaxies and the field, and again find an offset to lower metallicities (by ~ 0.05 dex) for a given mass. The smaller offset in the MZ relation indicates that both higher luminosities and lower metallicities may contribute to the shift of pairs relative to the control in the LZ relation. We show that the offset in the LZ relation depends on galaxy half light radius, r_h. Galaxies with r_h < 3 kpc and with a close companion show a 0.05-0.1 dex downwards offset in metallicity compared to control galaxies of the same size. Finally, we study the AGN fraction in both the pair and control sample and find that whilst selecting galaxies in different cuts of color and asymmetry yields different AGN fractions, the fraction for pairs and the control sample are consistent for a given set of selection criteria. 32] arXiv:0803.0251 [ps, pdf, other] Title: Mid-infrared Properties and Color Selection for X-ray Detected AGN in the MUSYC ECDF-S field Authors: Carolin N. Cardamone, C. Megan Urry, Maaike Damen, Pieter van Dokkum, Ezequiel Treister, Ivo Labbé, Shanil N. Virani, Paulina Lira, Eric Gawiser, for the MUSYC Collaboration Comments: 29 pages, including 7 figures. Accepted for publication in the Astrophysical Journal License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) We present the mid-infrared colors of X-ray-detected AGN and explore mid-infrared selection criteria. Using a statistical matching technique, the likelihood ratio, over 900 IRAC counterparts were identified with a new MUSYC X-ray source catalog that includes ~1000 published X-ray sources in the Chandra Deep Field-South and Extended Chandra Deep Field-South. Most X-ray-selected AGN have IRAC spectral shapes consistent with power-law slopes, f_{nu} ~ nu^{alpha}, and display a wide range of colors, -2 < alpha < 2. Although X-ray sources typically fit to redder (more negative alpha) power-laws than non-X-ray detected galaxies, more than 50% do have flat or blue (galaxy-like) spectral shapes in the observed 3-8 micron band. Only a quarter of the X-ray selected AGN detected at 24 micron are well fit by featureless red power laws in the observed 3.6-24 micron, likely the subset of our sample whose infrared spectra are dominated by emission from the central AGN region. Most IRAC color-selection criteria fail to identify the majority of X-ray-selected AGN, finding only the more luminous AGN, the majority of which have broad emission lines. In deep surveys, these color-selection criteria select 10-20% of the entire galaxy population and miss many moderate luminosity AGN. [26] arXiv:0803.0464 [ps, pdf, other] Title: The stellar population histories of early-type galaxies. III. The Coma Cluster Authors: S.C. Trager (1), S.M. Faber (2), Alan Dressler (3) ((1) Kapteyn Astronomical Institute, (2) UCO/Lick Observatory, (3) OCIW) Comments: 49 pages, 20 figures (19 EPS, 1 JPEG). MNRAS, in press. For version with full resolution of Fig. 1 see this http URL; for Table 2, see this http URL; for Table B3, see this http URL License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) We present stellar population parameters of twelve early-type galaxies (ETGs) in the Coma Cluster based on spectra obtained using the Low Resolution Imaging Spectrograph on the Keck II Telescope. Our data allow us to examine in detail the zero-point and scatter in their stellar population properties. Our ETGs have SSP-equivalent ages of on average 5-8 Gyr with the models used here, with the oldest galaxies having ages of ~10 Gyr old. This average age is identical to the mean age of field ETGs. Our ETGs span a large range in velocity dispersion but are consistent with being drawn from a population with a single age. Specifically, ten of the twelve ETGs are consistent within their formal errors of having the same age, 5.2+/-0.2 Gyr, over a factor of more than 750 in mass. We therefore find no evidence for downsizing of the stellar populations of ETGs in the core of the Coma Cluster. We suggest that Coma Cluster ETGs may have formed the majority of their mass at high redshifts but suffered small but detectable star formation events at z~0.1-0.3. Previous detections of 'downsizing' from stellar populations of local ETGs may not reflect the same downsizing seen in lookback studies of RSGs, as the young ages of the local ETGs represent only a small fraction of their total masses. (abridged) 28] arXiv:0803.0468 [ps, pdf, other] Title: MOND and the More Fundamental Plane Authors: R.H. Sanders, D.D. Land Comments: 6 pages, 5 figures, submitted to MNRAS License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) Bolton et al. (2007) have derived a mass-based fundamental plane using photometric and spectroscopic observations of 36 strong gravitational lenses. The lensing allows a direct determination of the mass-surface density and so avoids the usual dependence on mass-to-light ratio. We consider this same sample in the context of modified Newtonian dynamics (MOND) and demonstrate that the observed mass-based fundamental plane coincides with the MOND fundamental plane determined previously for a set of high-order polytropic spheres chosen to match the observed range of effective radii and velocity dispersions in elliptical galaxies. Moreover, the observed projected mass within one-half an effective radius is consistent with the mass in visible stars plus a small additional component of ``phantom dark matter'' resulting from the MOND contribution to photon deflection. [3] arXiv:0803.0545 [ps, pdf, other] Title: Merger and Ring Galaxy Formation Rates at z<2 Authors: E. D'Onghia, M. Mapelli, B. Moore (University of Zurich) Comments: Submitted to MNRAS. Revised version to match the referee's report License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) We compare the observed merger rate of galaxies over cosmic time and the frequency of collisional ring galaxies (CRGs), with analytic models and halo merger and collision rates from a large cosmological simulation. In the Lambda cold dark matter (LCDM) model we find that the cosmic {\it merger fraction} does not evolve strongly between 0.2~7 and constrain the UV LF within the first 700 Myrs. Our data set includes ~23 arcmin^2 of deep NICMOS J+H imaging data and ~248 arcmin^2 of ground-based imaging (ISAAC+MOIRCS) data. In total, we find 8 z~7.4 z-dropouts in our search fields, but no z~10 J-dropout candidates. A careful consideration of a wide variety of different contaminants suggest an overall contamination level of just ~12% for our z-dropout selection. After performing detailed simulations to accurately estimate the selection volumes, we derive constraints on the UV LFs at z~7-8 and z~10. For a faint-end slope alpha=-1.74, our most likely values for M*(UV) and phi* at z~7.4 are -19.8+/-0.4 mag and 1.1_{-0.7}^{+1.7}x10^{-3} Mpc^{-3}, respectively. Our search results for z~10 J-dropouts set a 1 sigma lower limit on M*(UV) of -19.6 mag assuming that phi* and alpha are the same as their values at slightly later times. This lower limit on M*(UV) is 1.4 mag fainter than our best-fit value at z~3.8, suggesting that the UV LF has undergone substantial evolution over this time period. No evolution is ruled out at 99% confidence from z~7.4 to z~6 and at 80% confidence from z~10 to z~7.4. The inferred brightening in M*(UV) with redshift (i.e., M*(UV) = (-21.02+/-0.09) + (0.36+/-0.08) (z - 3.8)) matches the evolution expected in the halo mass function, if the mass-to-light ratio of halos is assumed to evolve as ~(1+z)^{-1}. Finally, we consider the shape of the UV LF at z>~5 and discuss the implications of the Schechter-like form of the observed LFs, particularly the abrupt cut-off at the bright end. [17] arXiv:0803.0586 [ps, pdf, other] Title: Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data Authors: J. Dunkley, E. Komatsu, M. R. Nolta, D. N. Spergel, D. Larson, G. Hinshaw, L. Page, C. L. Bennett, B. Gold, N. Jarosik, J. L. Weiland, M. Halpern, R. S. Hill, A. Kogut, M. Limon, S. S. Meyer, G. S. Tucker, E. Wollack, E. L. Wright Comments: 57 pages, 21 figures, submitted to ApJS. For higher quality figs, see version on this http URL License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) This paper focuses on cosmological constraints derived from analysis of WMAP data alone. A simple LCDM cosmological model fits the five-year WMAP temperature and polarization data. The basic parameters of the model are consistent with the three-year data and now better constrained: Omega_b h^2 = 0.02273+-0.00062, Omega_c h^2 = 0.1099+-0.0062, Omega_L = 0.742+-0.030, n_s = 0.963+0.014- 0.015, tau = 0.087+-0.017, sigma_8 = 0.796+-0.036. With five years of polarization data, we have measured the optical depth to reionization, tau>0, at 5 sigma significance. The redshift of an instantaneous reionization is constrained to be z_reion = 11.0+-1.4 with 68% confidence. This excludes a sudden reionization of the universe at z=6 at more than 3.5 sigma significance, suggesting that reionization was an extended process. Using two different methods for polarized foreground cleaning, and foreground marginalization, we get consistent estimates for the optical depth. This cosmological model also fits small-scale CMB data, and a range of astronomical data measuring the expansion rate and clustering of matter in the universe. We find evidence for the first time in the CMB power spectrum for a non-zero cosmic neutrino background, or a background of relativistic species, with the standard three light neutrino species preferred over the best-fit LCDM model with N_eff=0 at >99.5% confidence, and N_eff > 2.3 (95% CL) when varied. The five-year WMAP data improve the upper limit on the tensor-to-scalar ratio to r < 0.43 (95% CL), for power-law models. With longer integration we find no evidence for a running spectral index, with dn_s/dlnk = -0.037+-0.028. [20] arXiv:0803.0598 [ps, pdf, other] Title: Galaxy Clusters in the Line of Sight to Background Quasars: I. Survey Design and Incidence of MgII Absorbers at Cluster Redshifts Authors: S. Lopez (1), L. F. Barrientos (2), P. Lira (1), N. Padilla (2), D. G. Gilbank (3), M. D. Gladders (4), J. Maza (1), N. Tejos (1), M. Vidal (1), H. K. C. Yee (3) ((1) Universidad de Chile; (2) Pontificia Universidad Catolica de Chile; (3) University of Toronto; (4) University of Chicago) Comments: Accepted for publication in the Astrophysical Journal License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ Subjects: Astrophysics (astro-ph) We describe the first optical survey of absorption systems associated with galaxy clusters at z= 0.3-0.9. We have cross-correlated SDSS DR3 quasars with high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. We have found 442 quasar-cluster pairs for which the MgII doublet might be detected at a transverse (physical) distance d<2 Mpc from the cluster centers. To investigate the incidence (dN/dz) and equivalent-width distribution n(W) of MgII systems at cluster redshifts, two statistical samples were drawn out of these pairs: one made of high-resolution spectroscopic quasar observations (46 pairs), and one made of quasars used in MgII searches found in the literature (375 pairs). The results are: (1) the population of strong MgII systems (W_0>2.0 Ang.) near cluster redshifts shows a significant (>3 sigma) overabundance (up to a factor of 15) when compared with the 'field' population; (2) the overabundance is more evident at smaller distances (d<1 Mpc) than larger distances (d<2 Mpc) from the cluster center; and, (3) the population of weak MgII systems (W_0<0.3 Ang.) near cluster redshifts conform to the field statistics. Unlike in the field, this dichotomy makes n(W) in clusters appear flat and well fitted by a power-law in the entire W-range. A sub-sample of the most massive clusters yields a stronger and still significant signal. Since either the absorber number density or filling-factor/cross-section affects the absorber statistics, an interesting possibility is that we have detected the signature of truncated halos due to environmental effects. Thus, we argue that the excess of strong systems is due to a population of absorbers in an overdense galaxy environment, and the lack of weak systems to a different population, that got destroyed in the cluster environment. (Abridged) 46] arXiv:0803.0732 [ps, pdf, other] Title: Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results Authors: G. Hinshaw, J. L. Weiland, R. S. Hill, N. Odegard, D. Larson, C. L. Bennett, J. Dunkley, B. Gold, M. R. Greason, N. Jarosik, E. Komatsu, M. R. Nolta, L. Page, D. N. Spergel, E. Wollack, M. Halpern, A. Kogut, M. Limon, S. S. Meyer, G. S. Tucker, E. L. Wright Comments: 43 pages, 13 figures, and 6 tables. Also available at this http URL License: http://creativecommons.org/licenses/publicdomain/ Subjects: Astrophysics (astro-ph) We present new full-sky temperature and polarization maps in five frequency bands from 23 to 94 GHz, based on data from the first five years of the WMAP sky survey. The five-year maps incorporate several improvements in data processing made possible by the additional years of data and by a more complete analysis of the instrument calibration and in-flight beam response. We present several new tests for systematic errors in the polarization data and conclude that Ka band data (33 GHz) is suitable for use in cosmological analysis, after foreground cleaning. This significantly reduces the overall polarization uncertainty. With the 5 year WMAP data, we detect no convincing deviations from the minimal 6-parameter LCDM model: a flat universe dominated by a cosmological constant, with adiabatic and nearly scale-invariant Gaussian fluctuations. Using WMAP data combined with measurements of Type Ia supernovae and Baryon Acoustic Oscillations, we find (68% CL uncertainties): Omega_bh^2 = 0.02265 \pm 0.00059, Omega_ch^2 = 0.1143 \pm 0.0034, Omega_Lambda = 0.721 \pm 0.015, n_s = 0.960 \pm 0.014, tau = 0.084 \pm 0.016, and Delta_R^2 = (2.457 \pm 0.093) x 10^-9. From these we derive: sigma_8 = 0.817 \pm 0.026, H_0 = 70.1 \pm 1.3 km/s/Mpc, z_{reion} = 10.8 \pm 1.4, and t_0 = 13.73 \pm 0.12 Gyr. The new limit on the tensor-to-scalar ratio is r < 0.20 (95% CL). We obtain tight, simultaneous limits on the (constant) dark energy equation of state and spatial curvature: -0.11 < 1+w < 0.14 and -0.0175 < Omega_k < 0.0085 (both 95% CL). The number of relativistic degrees of freedom (e.g. neutrinos) is found to be N_{eff} = 4.4 \pm 1.5, consistent with the standard value of 3.04. Models with N_{eff} = 0 are disfavored at >99.5% confidence.