Observations of H I absorbing gas in compact radio sources at cosmological redshifts

¹ Netherlands Foundation for Research in Astronomy (ASTRON), PO Box 2, 7990 AA Dwingeloo, The Netherlands
² National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
³ Onsala Space Observatory, 439 92 Onsala, Sweden
⁴ Leiden Observatory, PO Box 9513, 2300RA Leiden, The Netherlands
⁵ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
⁶ Space Telescope Science Institute, Baltimore, USA
⁷ Lawrence Livermore National Laboratories, USA
⁸ Astrophysics Department, University of Bristol, Great Britain
⁹ Joint Institute for VLBI in Europe (JIVE), Postbus 2, 7990 AA Dwingeloo, The Netherlands
¹⁰ Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK

Corresponding author: R. C. Vermeulen, rvermeulen@astron.nl

Received: 17 February 2002
Accepted: 20 March 2003

Abstract

We present an overview of the occurrence and properties of atomic gas associated with compact radio sources at redshifts up to . Searches for H i 21 cm absorption were made with the Westerbork Synthesis Radio Telescope at UHF-high frequencies (725–1200 MHz). Detections were obtained for 19 of the 57 sources with usable spectra (33%). We have found a large range in line depths, from to . There is a substantial variety of line profiles, including Gaussians of less than 10 km s^-1, to more typically 150 km s^-1, as well as irregular and multi-peaked absorption profiles, sometimes spanning several hundred km s^-1. Assuming uniform coverage of the entire radio source, we obtain column depths of atomic gas between and ( K)() cm^-2. There is evidence for significant gas motions, but in contrast to earlier results at low redshift, there are many sources in which the H i velocity is substantially negative (up to  km s^-1) with respect to the optical redshift, suggesting that in these sources the atomic gas, rather than falling into the centre, may be be flowing out, interacting with the jets, or rotating around the nucleus.