A deep search for 21cm absorption in high redshift damped Lyman-$α$ systems
| dc.creator | Kanekar, Nissim | |
| dc.creator | Chengalur, Jayaram N | |
| dc.date | 2002-11-28 | |
| dc.date.accessioned | 2026-07-07T10:31:31Z | |
| dc.date.available | 2026-07-07T10:31:31Z | |
| dc.description | We present deep GMRT 21cm absorption spectra of 10 damped Lyman-$α$ systems (DLAs), of which 8 are at redshifts $z \ga 1.3$. HI absorption was detected in only one DLA, the $z = 0.5318$ absorber toward PKS 1629+12, which has been identified with a luminous spiral galaxy; the spin temperature limit ($T_s \le 310$ K) derived from our observations continues the trend of DLAs associated with bright spirals having low spin temperatures. In 7 of the remaining 9 systems, the observations place strong lower limits on the spin temperature of the HI gas. The sample of DLAs searched for 21cm absorption now consists of 31 systems, with $T_s$ estimates available in 24 cases; of these, 16 are at $z < 2$ and 8 at $z > 2$, with 11 (all at $z < 1$) having optical IDs. For the latter 11 systems, we find that all low $T_s$ DLAs have been identified with luminous galaxies, while all high $T_s$ ($T_s \ga 1000$ K) DLAs have been identified with either LSBs or dwarfs. DLA spin temperatures thus appear to correlate with galaxy type, with no correlation seen between $T_s$ and impact parameter. The trend that low $z$ DLAs exhibit both high and low $T_s$ values while high redshift ($z \ga 3$) DLAs only show high spin temperatures is present in this expanded data set. Based on this difference in spin temperatures, the Gehan test rules out the hypothesis that DLAs at $z > 2$ and DLAs at $z < 2$ are drawn from the same parent population at ~ 99 % confidence level. Finally, we estimate upper limits on the fraction of cold HI, $f_{CNM}$, in the $z \ga 3$ DLAs. In local spirals, $f_{CNM} \sim 0.5$; in contrast, we find that $f_{CNM} < 0.3$ in all 7 high $z$ DLAs, with $f_{CNM} < 0.1$ in 5 of the 7 cases. (abridged) | |
| dc.description | 13 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics | |
| dc.identifier | https://arxiv.org/abs/astro-ph/0211637 | |
| dc.identifier | http://arxiv.org/abs/astro-ph/0211637 | |
| dc.identifier | Astron.Astrophys.399:857,2003 | |
| dc.identifier | doi:10.1051/0004-6361:20021922 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/178438 | |
| dc.subject | Astrophysics | |
| dc.title | A deep search for 21cm absorption in high redshift damped Lyman-$α$ systems | |
| dc.type | text |