Sign on

SAO/NASA ADS Astronomy Abstract Service

· Find Similar Abstracts (with default settings below)
· Electronic Refereed Journal Article (HTML)
· Full Refereed Journal Article (PDF/Postscript)
· Full Refereed Scanned Article (GIF)
· arXiv e-print (arXiv:astro-ph/0606180)
· References in the article
· Citations to the Article (13) (Citation History)
· Refereed Citations to the Article
· SIMBAD Objects (70)
· NED Objects (34)
· Also-Read Articles (Reads History)
·
· Translate This Page
Title:
The detectability of HI 21-cm absorption in damped Lyman α systems
Authors:
Curran, S. J.; Webb, J. K.
Affiliation:
AA(School of Physics, University of New South Wales, Sydney, NSW 2052, Australia; ), AB(School of Physics, University of New South Wales, Sydney, NSW 2052, Australia; )
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 371, Issue 1, pp. 356-362. (MNRAS Homepage)
Publication Date:
09/2006
Origin:
MNRAS
MNRAS Keywords:
galaxies: ISM , quasars: absorption lines , cosmology: observations , early Universe
DOI:
10.1111/j.1365-2966.2006.10663.x
Bibliographic Code:
2006MNRAS.371..356C

Abstract

In this paper, we investigate the possible reasons why HI 21-cm absorption in damped Lyman α systems (DLAs) has only been detected at low redshift. To date, no 21-cm absorption has yet been detected at zabs > 2.3, and at redshifts less than this, there is a mix of detections and non-detections in the DLAs searched. This has been attributed to the morphologies of the galaxies hosting the DLAs, where at low redshift the DLAs comprise both large and compact galaxies, which are believed to have low and high spin temperatures, respectively. Likewise, at high redshift the DLA population is believed to consist exclusively of compact galaxies of high spin temperature. However, in a previous paper, we found that by not assuming or assigning an often uncertain value for the coverage of the radio continuum source by the 21-cm absorbing gas, that there is generally no difference in the spin temperature/covering factor ratio between the 21-cm detections and non-detections or between the low- and high-redshift samples. Furthermore, only one of the 18 non-detections has a known host morphology, thus making any link between morphology and 21-cm delectability highly speculative.

We suggest that the lack of 21-cm absorption detections at high redshift arises from the fact that these DLAs are at similar angular diameter distances to the background quasars (i.e. the distance ratios are always close to unity). Above zabs ~ 1.6, the covering factor becomes largely independent of the DLA-QSO distance, making the high-redshift absorbers much less effective at covering the background continuum emission. At low redshift, small distance ratios are strongly favoured by the 21-cm detections, whereas large ratios are favoured by the non-detections. This mix of distance ratios gives the observed mix of detections and non-detections at zabs <~ 1.6. In addition to the predominance of large distance ratios and non-detections at high redshift, this strongly suggests that the observed distribution of 21-cm absorption in DLAs is dominated by geometric effects.

Printing Options

Print whole paper
Print Page(s) through

Return 600 dpi PDF to Acrobat/Browser. Different resolutions (200 or 600 dpi), formats (Postscript, PDF, etc), page sizes (US Letter, European A4, etc), and compression (gzip,compress,none) can be set through the Printing Preferences


More Article Retrieval Options

HELP for Article Retrieval
Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)
   

Find Similar Abstracts:

Use: Authors
Title
Keywords (in text query field)
Abstract Text
Return: Query Results Return    items starting with number
Query Form
Database: Astronomy
Physics
arXiv e-prints