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The Fueling Diagram: Linking Galaxy Molecular-to-Atomic Gas Ratios to Interactions and Accretion

David V. Stark, Sheila J. Kannappan, Lisa H. Wei, Andrew J. Baker, Adam K. Leroy, Kathleen D. Eckert, Stuart N. Vogel

To assess how external factors such as local interactions and fresh gas accretion influence the global ISM of galaxies, we analyze the relationship between recent enhancements of central star formation and total molecular-to-atomic (H2/HI) gas ratios, using a broad sample of field galaxies spanning early-to-late type morphologies, stellar masses of 10^(7.2-11.2) Msun, and diverse stages of evolution. We find that galaxies occupy several loci in a "fueling diagram" that plots H2/HI vs. mass-corrected blue-centeredness, a metric tracing the degree to which galaxies have bluer centers than the average galaxy at their stellar mass. Spiral galaxies show a positive correlation between H2/HI and mass-corrected blue-centeredness. When combined with previous results linking mass-corrected blue-centeredness to external perturbations, this correlation suggests a link between local galaxy interactions and molecular gas inflow/replenishment. Intriguingly, E/S0 galaxies show a more complex picture: some follow the same correlation, some are quenched, and a distinct population of blue-sequence E/S0 galaxies (with masses below key transitions in gas richness) defines a separate loop in the fueling diagram. This population appears to be composed of low-mass merger remnants currently in late- or post-starburst states, in which the burst first consumes the H2 while the galaxy center keeps getting bluer, then exhausts the H2, at which point the burst population reddens as it ages. Multiple lines of evidence suggest connected evolutionary sequences in the fueling diagram. In particular, tracking total gas-to-stellar mass ratios within the diagram provides evidence of fresh gas accretion onto low-mass E/S0s emerging from central starbursts. Drawing on a comprehensive literature search, we suggest that virtually all galaxies follow the same evolutionary patterns found in our broad sample.


A Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34

Dominik A. Riechers (Cornell, Caltech), C.M. Bradford, D.L. Clements, C.D. Dowell, I. Perez-Fournon, R.J. Ivison, C. Bridge, A. Conley, Hai Fu, J.D. Vieira, J. Wardlow, J. Calanog, A. Cooray, P. Hurley, R. Neri, J. Kamenetzky, J.E. Aguirre, B. Altieri, V. Arumugam, D.J. Benford, M. Bethermin, J. Bock, D. Burgarella, A. Cabrera-Lavers, S.C. Chapman, P. Cox, J.S. Dunlop, L. Earle, D. Farrah, P. Ferrero, A. Franceschini, R. Gavazzi, J. Glenn, E.A. Gonzalez Solares, M.A. Gurwell, M. Halpern, E. Hatziminaoglou, A. Hyde, E. Ibar, A. Kovacs, M. Krips, R.E. Lupu, P.R. Maloney, P. Martinez-Navajas, H. Matsuhara, E.J. Murphy, B.J. Naylor, H.T. Nguyen, S.J. Oliver, A. Omont, M.J. Page, G. Petitpas, N. Rangwala, I.G. Roseboom, D. Scott, A.J. Smith, J.G. Staguhn, A. Streblyanska, A.P. Thomson, I. Valtchanov,

Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts – that is, increased rates of star formation – in the most massive dark matter halos at early epochs. However, it remains unknown how soon after the Big Bang such massive starburst progenitors exist. The measured redshift distribution of dusty, massive starbursts has long been suspected to be biased low in redshift owing to selection effects, as confirmed by recent findings of systems out to redshift z~5. Here we report the identification of a massive starburst galaxy at redshift 6.34 through a submillimeter color-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40% of the baryonic mass. A "maximum starburst" converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn of cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang


An ALMA survey of submillimeter galaxies in the Extended Chandra Deep Field South: Source catalog and multiplicity

J. A. Hodge, A. Karim, I. Smail, A. M. Swinbank, F. Walter, A. D. Biggs, R. J. Ivison, A. Weiss, D. M. Alexander, F. Bertoldi, W. N. Brandt, S. C. Chapman, K. E. K. Coppin, P. Cox, A. L. R. Danielson, H. Dannerbauer, C. De Breuck, R. Decarli, A. C. Edge, T. R. Greve, K. K. Knudsen, K. M. Menten, H.-W. Rix, E. Schinnerer, J. M. Simpson, J. L. Wardlow, P. van der Werf

We present an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 survey of 126 submillimeter sources from the LABOCA ECDFS Submillimeter Survey (LESS). Our 870 micron survey with ALMA (ALESS) has produced maps ~3X deeper and with a beam area ~200X smaller than the original LESS observations, doubling the current number of interferometrically-observed submillimeter sources. The high resolution of these maps allows us to resolve sources that were previously blended and accurately identify the origin of the submillimeter emission. We discuss the creation of the ALESS submillimeter galaxy (SMG) catalog, including the main sample of 99 SMGs and a supplementary sample of 32 SMGs. We find that at least 35% (possibly up to 50%) of the detected LABOCA sources have been resolved into multiple SMGs, and that the average number of SMGs per LESS source increases with LESS flux density. Using the (now precisely known) SMG positions, we empirically test the theoretical expectation for the uncertainty in the single-dish source positions. We also compare our catalog to the previously predicted radio/mid-infrared counterparts, finding that 45% of the ALESS SMGs were missed by this method. Our ~1.6" resolution allows us to measure a size of ~9 kpc X 5 kpc for the rest-frame ~300 um emission region in one resolved SMG, implying a star formation rate surface density of 80 M_sol yr^-1 kpc^-2, and we constrain the emission regions in the remaining SMGs to be <10 kpc. As the first statistically reliable survey of SMGs, this will provide the basis for an unbiased multiwavelength study of SMG properties.

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