Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Molecular gas at intermediate redshifts   We present Giant Metrewave Radio Telescope (GMRT) observations of OH
absorption in B3~1504+377 ($z \sim 0.673$) and PKS 1413+135 ($z \sim 0.247$).
OH has now been detected in absorption towards four intermediate redshift
systems, viz. the lensing galaxies towards B~0218+357 ($z \sim 0.685$; Kanekar
et al. 2001) and 1830-211 ($z \sim 0.886$; Chengalur et al. 1999), in addition
to the two systems listed above. All four systems also give rise to well
studied millimetre wavelength molecular line absorption from a host of
molecules, including HCO$^+$. Comparing our OH data with these millimetre line
transitions, we find that the linear correlation between $N_{\rm OH}$ and
$N_{\rm HCO^+}$ found in molecular clouds in the Milky Way (Liszt & Lucas 1996)
persists out to $z \sim 1$. It has been suggested (Liszt & Lucas 1999) that OH
is a good tracer of ${\rm H_2}$, with $N_{\rm H_2}/N_{\rm OH} \approx 10^7$
under a variety of physical conditions. We use this relationship to estimate
$N_{\rm H_2}$ in these absorbers. The estimated $N_{\rm H_2}$ is $\ga 10^{22}$
in all four cases and substantially different from estimates based on CO
observations.

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The categories of this paper are: alg-geom
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The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
0
The categories of this paper are: hep-ph