The ALMA Spectroscopic Survey in the HUDF: CO Luminosity Functions and the Molecular Gas Content of Galaxies through Cosmic History

Roberto Decarli (1) , Fabian Walter (1) , Jorge Gónzalez-López , Manuel Aravena , Leindert Boogaard (2) , Chris Carilli (3) , Pierre Cox , Emanuele Daddi (4) , Gergö Popping , Dominik Riechers (5) , Bade Uzgil , Axel Weiss (6) , Roberto J Assef , Roland Bacon , Franz Erik Bauer , Frank Bertoldi , Rychard Bouwens , Thierry Contini (7) , Paulo C Cortes , Elisabete da Cunha (8) , Tanio Díaz-Santos , David Elbaz , Hanae Inami , Jacqueline Hodge , Rob Ivison , Olivier Le Fevre (9) , Benjamin Magnelli , Mladen Novak , Pascal Oesch , Hans-Walter Rix , Mark Sargent (10) , Ian Smail , A. Mark Mark Swinbank , Rachel S Somerville , Paul van Der Werf , Jeff Wagg , Lutz Wisotzki

1 MPIA - Max-Planck-Institut für Astronomie
2 Leiden Observatory [Leiden]
3 NRAO - National Radio Astronomy Observatory [Socorro]
4 DAP - Département d'Astrophysique (ex SAP)
5 Cornell University [New York]
6 Millimeter and Submillimeter Astronomy
7 IRAP - Institut de recherche en astrophysique et planétologie
8 IAP - Institut d'Astrophysique de Paris
9 LAM - Laboratoire d'Astrophysique de Marseille
10 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation

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(H 2). 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-H 2 conversion factor, we constrain the evolution of the cosmic molecular gas density ρ(H 2): 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(H 2), 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(H 2) 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).

Domaines: Astrophysique [astro-ph]

Roberto Decarli, Fabian Walter, Jorge Gónzalez-López, Manuel Aravena, Leindert Boogaard, et al.. The ALMA Spectroscopic Survey in the HUDF: CO Luminosity Functions and the Molecular Gas Content of Galaxies through Cosmic History. The Astrophysical Journal, 2019, 882 (2), pp.138. ⟨10.3847/1538-4357/ab30fe⟩. ⟨hal-02325055⟩