Evolution of Cosmic Molecular Gas Mass Density From z ~ 0 to z = 1 -1.5

Abstract

We try to constrain the cosmic molecular gas mass density at $z=1-1.5$ and that in the local universe by combining stellar mass functions of star-forming galaxies and their average molecular gas mass fractions against the stellar mass. The average molecular gas mass fractions are taken from recent CO observations of star-forming galaxies at the redshifts. The cosmic molecular gas mass density is obtained to be ${\rho }_{{\mathrm{H}}_2}=(6.8-8.8)\times 10^7{M}_{\odot }{\mathrm{Mpc}}^{-3}$ at $z=1-1.5$ and $6.7\times 10^6{M}_{\odot }{\mathrm{Mpc}}^{-3}$ at $z\sim 0$ by integrating down to $0.03M^{\ast }$. Although the values have various uncertainties, the cosmic molecular gas mass density at $z=1-1.5$ is about ten times larger than that in the local universe. The cosmic star formation rate density at $z\sim 1-2$ is also about ten times larger than that in the local universe. Our result suggests that the large cosmic molecular gas mass density at $z=1-1.5$ accounts for the large cosmic star formation rate density at $z\sim 1-2$.

6 pages, 2 figures, Accepted for publication in the ApJ

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• Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS): II. Cold Molecular Gas Evolution out to Redshift 6
• The relationship between the incidence of X-ray selected AGN in nearby galaxies and star-formation rate
• The relationship between cluster environment and molecular gas content of star-forming galaxies in the EAGLE simulation
• Internal structure of molecular gas in a main sequence galaxy with a UV clump at z = 1.45