Abstract
Abstract We try to constrain the cosmic molecular gas mass density (CMGD) at 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 CMGD is obtained to be at and at by integrating down to . Although the values have various uncertainties, the CMGD at is about 10 times larger than that in the local universe. The cosmic star formation rate density (CSFRD) at is also about 10 times larger than that in the local universe. Our result suggests that the large CMGD at accounts for the large CSFRD at .
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