We present an overview of the occurrence and properties of atomic gas associated with compact radio sources at redshifts up to z = 0.85. Searches for Hi 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 r = 0.16 to r<= 0.001. There is a substantial variety of line profiles, including Gaussians of less than 10 kms^−1, to more typically 150 kms^−1, as well as irregular and multi-peaked absorption profiles, sometimes spanning several hundred kms^−1. Assuming uniform coverage of the entire radio source, we obtain column depths of atomic gas between 1×10^19 and 3.3×10^21 (Tsp/100 K)(1/f) 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 Hi velocity is substantially negative (up to v = −1420 kms^−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 (Refer to PDF file for exact formulas).

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Also archived in: arXiv: astro-ph/0304291 v1 15 Apr 2003 The WSRT is operated by ASTRON (The Netherlands Foundation for Research in Astronomy) with support from the Netherlands Foundation for Scientific Research (NWO). We are very grateful for the dedication of the ASTRON staff who worked on the WSRT upgrade, as well as those who assisted in performing the survey observations. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration in the United States of America.ISSN:1432-0746 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

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Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus