arXiv:0905.1674 [ps, pdf, other] Title: Star formation and dust obscuration at z~2: galaxies at the dawn of downsizing Authors: M. Pannella (NRAO), C.L. Carilli (NRAO), E. Daddi (CEA), H.J. Mc Cracken (IAP), F.N. Owen (NRAO), A. Renzini (INAF-Padova), V. Strazzullo (NRAO), F. Civano (CfA), A.M. Koekemoer (STScI), E. Schinnerer (MPIA), N. Scoville (CIT), V. Smolcic (CIT), Y. Taniguchi (GSSE), H. Aussel (CEA), J.P. Kneib (LAM), O. Ilbert (IfA/LAM), Y. Mellier (IAP), M. Salvato (CIT), D. Thompson (LBTO/UofA), C.J. Willott (NRC-HIA) Comments: 5 pages, 5 figures. Accepted for publication in Astrophysical Journal Letters Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) We present first results of a study aimed to constrain the star formation rate and dust content of galaxies at z~2. We use a sample of BzK-selected star-forming galaxies, drawn from the COSMOS survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after removing AGN contaminants from the sample. Dust unbiased star formation rates are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: i) specific star formation rates are constant over about 1 dex in stellar mass and up to the highest stellar mass probed; ii) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects; iii) a single value of the UV extinction applied to all galaxies would lead to grossly underestimate the SFR in massive galaxies; iv) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provide results in very good agreement with the radio derived ones; v) the mean specific star formation rate of our sample steadily decreases by a factor of ~4 with decreasing redshift from z=2.3 to 1.4 and a factor of ~40 down the local Universe. These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts, we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies. arXiv:0905.1689 [ps, pdf, other] Title: Growing the first bright quasars in cosmological simulations of structure formation Authors: Debora Sijacki (1), Volker Springel (2), Martin G. Haehnelt (1) ((1) Institute of Astronomy, University of Cambridge, (2) Max-Planck-Institute for Astrophysics, Garching) Comments: 26 pages, 19 figures, MNRAS submitted Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA) We employ cosmological hydrodynamical simulations to study the growth of massive black holes (BHs) at high redshifts subject to BH merger recoils from gravitational wave emission. We select the most massive dark matter halo at z=6 from the Millennium simulation, and resimulate its formation at much higher resolution including gas physics and a model for BH seeding, growth and feedback. Assuming that the initial BH seeds are relatively massive, of the order of 10^5 Msun, and that seeding occurs around z~15 in dark matter haloes of mass 10^9-10^10 Msun, we find that it is possible to build up supermassive BHs (SMBHs) by z=6 that assemble most of their mass during extended Eddington-limited accretion periods. The properties of the simulated SMBHs are consistent with observations of z=6 quasars in terms of the estimated BH masses and bolometric luminosities, the amount of star formation occurring within the host halo, and the presence of highly enriched gas in the innermost regions of the host galaxy. After a peak in the BH accretion rate at z=6, the most massive BH has become sufficiently massive for the growth to enter into a much slower phase of feedback-regulated accretion. We explore the full range of expected recoils and radiative efficiencies, and also consider models with spinning BHs. In the most `pessimistic' case where BH spins are initially high, we find that the growth of the SMBHs can be potentially hampered if they grow mostly in isolation and experience only a small number of mergers. Whereas BH kicks can expel a substantial fraction of low mass BHs, they do not significantly affect the build up of the SMBHs. On the contrary, a large number of BH mergers has beneficial consequences for the growth of the SMBHs by considerably reducing their spin. [Abridged] arXiv:0905.1691 [ps, pdf, other] Title: Stellar sources of dust in the high redshift Universe Authors: Rosa Valiante, Raffaella Schneider, Simone Bianchi, Anja C. Andersen Comments: 12 pages, 7 figures, accepted for pubblication in MNRAS Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) With the aim of investigating whether stellar sources can account for the >10^8 Msun dust masses inferred from mm/sub-mm observations of samples of 54. The fact that a source like HDF 850.1 should have appeared in one of the very first blank-field SCUBA observations ever made suggests that such high-redshift sources are quite common. Thus, we are led to conclude that high-redshift star formation is dominated by giant dusty star-forming galaxies, just as it is at lower redshifts. arXiv:0905.1956 [ps, pdf, other] Title: An Evolutionary Paradigm for Dusty Active Galaxies at Low Redshift Authors: D. Farrah (Sussex), B. Connolly (Pennsylvania), N. Connolly (Hamilton College), H. Spoon (Cornell), S. Oliver (Sussex), H. Prosper (Florida State), L. Armus (Caltech), J. R. Houck (Cornell), A. R. Liddle (Sussex), V. Desai (Caltech) Comments: ApJ accepted. Comments welcome. We suggest reading section 2 before looking at the figures. 26 pages, 21 figures, 1 table Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) We apply methods from Bayesian inferencing and graph theory to a dataset of 102 mid-infrared spectra, and archival data from the optical to the millimeter, to construct an evolutionary paradigm for z<0.4 infrared-luminous galaxies (ULIRGs). We propose that the ULIRG lifecycle consists of three phases. The first phase lasts from the initial encounter until approximately coalescence. It is characterized by homogeneous mid-IR spectral shapes, and IR emission mainly from star formation, with a contribution from an AGN in some cases. At the end of this phase, a ULIRG enters one of two evolutionary paths depending on the dynamics of the merger, the available quantities of gas, and the masses of the black holes in the progenitors. On one branch, the contributions from the starburst and the AGN to the total IR luminosity decline and increase respectively. The IR spectral shapes are heterogeneous, likely due to feedback from AGN-driven winds. Some objects go through a brief QSO phase at the end. On the other branch, the decline of the starburst relative to the AGN is less pronounced, and few or no objects go through a QSO phase. We show that the 11.2 micron PAH feature is a remarkably good diagnostic of evolutionary phase, and identify six ULIRGs that may be archetypes of key stages in this lifecycle. arXiv:0905.1958 [ps, pdf, other] Title: The edge of the M87 halo and the kinematics of the diffuse light in the Virgo cluster core Authors: Michelle Doherty, Magda Arnaboldi, Payel Das, Ortwin Gerhard, J. Alfonso L. Aguerri, Robin Ciardullo, John J. Feldmeier, Kenneth C. Freeman, George H. Jacoby, Giuseppe Murante Comments: Accepted for publication in Astronomy and Astrophysics. 16 pages, 14 figures and 4 tables Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA) We present high resolution FLAMES/VLT spectroscopy of intracluster planetary nebula (ICPN) candidates, targeting three new fields in the Virgo cluster core with surface brightness down to mu_B = 28.5. Based on the projected phase space information we separate the old and 12 newly-confirmed PNs into galaxy and intracluster components. The M87 PNs are confined to the extended stellar envelope of M87, within a projected radius of ~ 160 kpc, while the ICPNs are scattered across the whole surveyed region between M87 and M86. The velocity dispersions determined from the M87 PNs at projected radii of 60 kpc and 144 kpc show that the galaxy's velocity dispersion profile decreases in the outer halo, down to 78 +/- 25 km/s. A Jeans model for the M87 halo stars in the gravitational potential traced by the X-ray emission fits the observed velocity dispersion profile only if the stellar orbits are strongly radially anisotropic (beta ~= 0.4 at r ~= 10 kpc increasing to 0.8 at the outer edge), and if additionally the stellar halo is truncated at ~= 150 kpc average elliptical radius. From the spatial and velocity distribution of the ICPNs we infer that M87 and M86 are falling towards each other and that we may be observing them just before the first close pass. The inferred luminosity-specific PN numbers for the M87 halo and the ICL are in the range of values observed for old (> 10 Gyr) stellar populations (abridged). arXiv:0905.2180 [ps, pdf, other] Title: Global star formation revisited Authors: Joseph Silk, Colin Norman Comments: Astrophysical Journal, in press Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA) A general treatment of disk star formation is developed from a dissipative multi-phase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and Schmidt-Kennicutt law residuals. The model is extended to include a multi-phase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central AGN. During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift. arXiv:0905.2184 [ps, pdf, other] Title: The Star-Forming Molecular Gas in High Redshift Submillimeter Galaxies Authors: Desika Narayanan, Thomas J. Cox, Christopher Hayward, Joshua D. Younger, Lars Hernquist (CfA) Comments: Submitted to MNRAS; 19 pages, 12 figures. For full resolution manuscript, see this http URL Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) We present a model for the CO molecular line emission from high redshift Submillimeter Galaxies (SMGs). By combining hydrodynamic simulations of gas rich galaxy mergers with the polychromatic radiative transfer code, Sunrise, and the 3D non-LTE molecular line radiative transfer code, Turtlebeach, we show that if SMGs are typically a transient phase of major mergers, their observed compact CO spatial extents, broad line widths, and high excitation conditions (CO SED) are naturally explained. In this sense, SMGs can be understood as scaled-up analogs to local ULIRGs. We utilize these models to investigate the usage of CO as an indicator of physical conditions. We find that care must be taken when applying standard techniques. The usage of CO line widths as a dynamical mass estimator from SMGs can possibly overestimate the true enclosed mass by a factor ~1.5-2. At the same time, assumptions of line ratios of unity from CO J=3-2 (and higher lying lines) to CO (J=1-0) will oftentimes lead to underestimates of the inferred gas mass. We provide tests for these models by outlining predictions for experiments which are imminently feasible with the current generation of bolometer arrays and radio-wave spectrometers. arXiv:0905.2186 [ps, pdf, other] Title: Seeding the formation of cold gaseous clouds in Milky Way size halos Authors: Dušan Kereš, Lars Hernquist Comments: 5 pages, 3 figures, submitted to ApJ Letters Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA) We use one of the highest resolution cosmological SPH simulations to date to demonstrate that cold gaseous clouds form around Milky Way size galaxies. We further explore mechanisms responsible for their formation and show that a large fraction of clouds originate as a consequence of late-time filamentary "cold mode" accretion. Here, "cold/warm" filaments are not able to connect directly to galaxies, as they do at high redshift, but are instead susceptible to the combined action of cooling and Rayleigh-Taylor instabilities at intermediate radii within the halo, leading to the production of cold, dense pressure-confined clouds. Our mechanism directly seeds clouds from gas with substantial local overdensity, avoiding problems associated with slower processes and providing a channel for the origin of cloud complexes. These clouds can later "rain" onto galaxies, delivering fuel for star formation. Owing to the relatively large cross section of filaments and the net angular momentum carried by the gas, the clouds will be distributed in a flattened spheroid around a galaxy.