Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Primordial gas cooling behind shock waves in merging halos   We investigate thermal regime of the baryons behind shock waves arising in
the process of virialization of dark matter halos. We find a fraction of the
shocked gas cooled by radiation of HD molecules down to the temperature of the
cosmic microwave background (CMB): this fraction increases sharply from about
$f_{\rm c}\sim 10^{-3}$ for dark halos of $M=5\times 10^7\msun$ to $\sim 0.1$
for halos with $M=10^8\msun$ at $z=10$. We show, however, that further increase
of the mass does not lead to a significant growth of $f_{\rm c}$ -- the
assymptotic value for $M\gg 10^8\msun$ is of 0.2. We estimate star formation
rate associated with such shock waves, and show that it can be a small but not
negligible fraction of the star formation connected with cooling by HI and
H$_2$. We argue that extremely metal-poor low-mass stars in the Milky Way may
have been formed from primordial gas behind such shocks.

15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph