Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Linked evolution of gas and star formation in galaxies over cosmic
  history   We compare the cosmic evolution of star formation rates in galaxies with that
of their neutral hydrogen densities. We highlight the need for neutral hydrogen
to be continually replenished from a reservoir of ionized gas to maintain the
observed star formation rates in galaxies. Hydrodynamic simulations indicate
that the replenishment may occur naturally through gas infall, although
measured rates of gas infall in nearby galaxies are insufficient to match
consumption. We identify an alternative mechanism for this replenishment,
associated with expanding supershells within galaxies. Pre-existing ionized gas
can cool and recombine efficiently in the walls of supershells, molecular gas
can form in situ in shell walls, and shells can compress pre-existing molecular
clouds to trigger collapse and star formation. We show that this mechanism
provides replenishment rates sufficient to maintain both the observed HI mass
density and the inferred molecular gas mass density over the redshift range
0<z<5.

27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys