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The evolution of the baryons associated with galaxies averaged over cosmic time and space.

Walter, Fabian and Carilli, Chris and Neeleman, Marcel and Decarli, Roberto and Popping, Gergö and Somerville, Rachel S. and Aravena, Manuel and Bertoldi, Frank and Boogaard, Leindert and Cox, Pierre and da Cunha, Elisabete and Magnelli, Benjamin and Obreschkow, Danail and Riechers, Dominik and Rix, Hans-Walter and Smail, Ian and Weiss, Axel and Assef, Roberto J. and Bauer, Franz and Bouwens, Rychard and Contini, Thierry and Cortes, Paulo C. and Daddi, Emanuele and Diaz-Santos, Tanio and González-López, Jorge and Hennawi, Joseph and Hodge, Jacqueline A. and Inami, Hanae and Ivison, Rob and Oesch, Pascal and Sargent, Mark and van der Werf, Paul and Wagg, Jeff and Yung, L. Y. Aaron (2020) 'The evolution of the baryons associated with galaxies averaged over cosmic time and space.', Astrophysical journal., 902 (2). p. 111.

Abstract

We combine the recent determination of the evolution of the cosmic density of molecular gas (H2) using deep, volumetric surveys, with previous estimates of the cosmic density of stellar mass, star formation rate and atomic gas (H i), to constrain the evolution of baryons associated with galaxies averaged over cosmic time and space. The cosmic H i and H2 densities are roughly equal at z ~ 1.5. The H2 density then decreases by a factor ${6}_{-2}^{+3}$ to today's value, whereas the H i density stays approximately constant. The stellar mass density is increasing continuously with time and surpasses that of the total gas density (H i and H2) at redshift z ~ 1.5. The growth in stellar mass cannot be accounted for by the decrease in cosmic H2 density, necessitating significant accretion of additional gas onto galaxies. With the new H2 constraints, we postulate and put observational constraints on a two-step gas accretion process: (i) a net infall of ionized gas from the intergalactic/circumgalactic medium to refuel the extended H i reservoirs, and (ii) a net inflow of H i and subsequent conversion to H2 in the galaxy centers. Both the infall and inflow rate densities have decreased by almost an order of magnitude since z ~ 2. Assuming that the current trends continue, the cosmic molecular gas density will further decrease by about a factor of two over the next 5 Gyr, the stellar mass will increase by approximately 10%, and cosmic star formation activity will decline steadily toward zero, as the gas infall and accretion shut down.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.3847/1538-4357/abb82e
Publisher statement:Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Date accepted:13 August 2020
Date deposited:17 November 2020
Date of first online publication:19 September 2020
Date first made open access:17 November 2020

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