Almacal – VI. Molecular gas mass density across cosmic time via a blind search for intervening molecular absorbers
Journal article, 2019
We are just starting to understand the physical processes driving the dramatic change in cosmic star formation rate between z ∼ 2 and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, due to the large redshift path surveyed (z = 182), we provide constraints on the molecular column density distribution function beyond z ∼ 0. In addition, we probe column densities of N(H2) > 1016 atoms cm−2, 5 orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of ρ(H2) 108.3 M Mpc−3 at 0 < z ≤ 1.7 already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to z ∼ 2.
Galaxies: formation
Galaxies: evolution
Quasars: absorption lines
ISM: molecules
Author
Anne Klitsch
European Southern Observatory (ESO)
Durham University
Céline Péroux
Laboratoire d'Astrophysique de Marseille
European Southern Observatory (ESO)
M. A. Zwaan
European Southern Observatory (ESO)
I. Smail
Durham University
Dylan Nelson
Max Planck Society
Gergö Popping
Max Planck Society
C. C. Chen
European Southern Observatory (ESO)
Benedikt Diemer
Harvard-Smithsonian Center for Astrophysics
R. J. Ivison
European Southern Observatory (ESO)
University of Edinburgh
James R. Allison
University of Oxford
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
A. Mark Swinbank
Durham University
Aleksandra Hamanowicz
European Southern Observatory (ESO)
A. D. Biggs
European Southern Observatory (ESO)
Rajeshwari Dutta
European Southern Observatory (ESO)
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 490 1 1220-1230Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1093/mnras/stz2660