Associated HI in Absorbers at High Redshift
Abstract
WSRT observations have provided a first inventory of the incidence of HI 21 cm line absorption associated with AGN at redshifts up to z=1.0. There is a large range in line depths, from tau=0.44 to tau less than 0.001, and a substantial variety of line profiles, from Gaussians of less than ten km/s to more typically a few hundred km/s, as well as irregular and multi-peaked absorption, sometimes spanning many hundreds of km/s. The chance to detect appreciable HI absorption is greatest in the most compact radio sources, GPSs and CSOs, where it can occur in circumnuclear ``disks'' or ``tori'', as well as in gas enveloping jets and hot spots; inferred densities range at least between 10 per cubic cm and 10000 per cubic cm. But HI absorption occurs also in some CSSs, perhaps associated with jet-cloud interaction regions, and in quasars with a large optical reddening. VLBI observations at the unusual UHF frequencies of redshifted HI 21 cm can give unique ``sight''lines into the physics and evolution of young radio sources and their inner galactic medium.
Cite
@article{arxiv.astro-ph/0012352,
title = {Associated HI in Absorbers at High Redshift},
author = {R. C. Vermeulen},
journal= {arXiv preprint arXiv:astro-ph/0012352},
year = {2007}
}
Comments
4 pages, 2 postscript figures, LaTeX, uses paspiau199.sty. to appear in "The Universe at Low Radio Frequencies", IAU Symposium 199, ASP Conference Series, V.K. Kapahi & A.P. Rao (eds.)