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The ALMA Spectroscopic Survey in the HUDF : co luminosity functions and the molecular gas content of galaxies through cosmic history.

Decarli, Roberto and Walter, Fabian and Gónzalez-López, Jorge and Aravena, Manuel and Boogaard, Leindert and Carilli, Chris and Cox, Pierre and Daddi, Emanuele and Popping, Gergö and Riechers, Dominik and Uzgil, Bade and Weiss, Axel and Assef, Roberto J. and Bacon, Roland and Bauer, Franz Erik and Bertoldi, Frank and Bouwens, Rychard and Contini, Thierry and Cortes, Paulo C. and Cunha, Elisabete da and Díaz-Santos, Tanio and Elbaz, David and Inami, Hanae and Hodge, Jacqueline and Ivison, Rob and Fèvre, Olivier Le and Magnelli, Benjamin and Novak, Mladen and Oesch, Pascal and Rix, Hans-Walter and Sargent, Mark T. and Smail, Ian and Swinbank, A. Mark and Somerville, Rachel S. and Werf, Paul van der and Wagg, Jeff and Wisotzki, Lutz (2019) 'The ALMA Spectroscopic Survey in the HUDF : co luminosity functions and the molecular gas content of galaxies through cosmic history.', Astrophysical journaL., 882 (2). p. 138.


We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of ρ(H2). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ~2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to ~90%, depending on the assumptions on the faint end) of the total cosmic CO luminosity at z = 1.0–3.1. After correcting for CO excitation, and adopting a Galactic CO-to-H2 conversion factor, we constrain the evolution of the cosmic molecular gas density ρ(H2): this cosmic gas density peaks at z ~ 1.5 and drops by a factor of ${6.5}_{-1.4}^{+1.8}$ to the value measured locally. The observed evolution in ρ(H2), therefore, closely matches the evolution of the cosmic star formation rate density ρ SFR. We verify the robustness of our result with respect to assumptions on source inclusion and/or CO excitation. As the cosmic star formation history can be expressed as the product of the star formation efficiency and the cosmic density of molecular gas, the similar evolution of ρ(H2) and ρ SFR leaves only little room for a significant evolution of the average star formation efficiency in galaxies since z ~ 3 (85% of cosmic history).

Item Type:Article
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Publisher statement:© 2019. The American Astronomical Society. All rights reserved.
Date accepted:03 April 2019
Date deposited:08 October 2019
Date of first online publication:11 September 2019
Date first made open access:08 October 2019

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