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).
Department, Program, or Center
School of Physics and Astronomy (COS)
Astronomy and Astrophysics 404 (2003) 861-870
RIT – Main Campus