Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evolution of Cosmic Molecular Gas Mass Density From z ~ 0 to z = 1 -1.5   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 $\rho_{\rm H_2} =
(6.8-8.8)~\times~10^7~M_\odot~{\rm Mpc}^{-3}$ at $z=1-1.5$ and $6.7 \times
10^6~M_\odot~{\rm Mpc}^{-3}$ at $z \sim 0$ by integrating down to
$0.03~M^\ast$. 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 $z \sim 1 -2$.

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The categories of this paper are: eess
34
The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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The categories of this paper are: adap-org
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The categories of this paper are: stat