Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: HI gas in the rejuvenated radio galaxy 4C29.30   We report the results of our observations of HI absorption towards the
central region of the rejuvenated radio galaxy 4C29.30 (J0840+2949) with the
Giant Metrewave Radio Telescope (GMRT). The radio source has diffuse, extended
emission with an angular size of $\sim$520 arcsec (639 kpc) within which a
compact edge-brightened double-lobed source with a size of 29 arcsec (36 kpc)
is embedded. The absorption profile which is seen towards the central component
of the inner double is well resolved and consists of six components; all but
one of which appears to be red-shifted relative to the optical systemic
velocity. The neutral hydrogen column density is estimated to be
$N$(HI)=4.7$\times10^{21}$($T_s$/100)($f_c$/1.0) cm$^{-2}$, where $T_s$ and
$f_c$ are the spin temperature and covering factor of the background source
respectively. This detection reinforces a strong correlation between the
occurrence of HI absorption and rejuvenation of radio activity suggested
earlier, with the possibility that the red-shifted gas is fuelling the recent
activity.

29
The categories of this paper are: funct-an
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn