Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Molecular absorption lines at high redshift   The four known molecular absorption line systems at redshifts z$=$0.25--0.89
are discussed. Two of the systems originate in the galaxy hosting the
`background' AGN, while in two cases the absorption occurs in truely
intervening galaxies. Indirect evidence for the existence of very small scale
structure in the molecular ISM is presented. A new absorption line at z$=$0.89
towards PKS1830--211 opens up interesting possibilities to accurately derive
the mass of the lensing galaxy.

20
The categories of this paper are: acc-phys
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin