H i absorption towards nearby compact radio sources

We present the results of H i absorption measurements towards a sample of nearby compact steep-spectrum (CSS) and gigahertz-peaked spectrum (GPS) radio sources, the Compact Radio sources at Low Redshift (CORALZ) sample, using the Giant Metrewave Radio Telescope (GMRT). We observed a sample of 18 sources and find seven new detections. These sources are of lower luminosity than earlier studies of CSS and GPS objects, and we investigate any dependence of H i absorption features on radio luminosity. Within the uncertainties, the detection rates and column densities are similar to the more luminous objects, with the GPS objects exhibiting a higher detection rate than for the CSS objects. The relative velocity of the blueshifted absorption features, which may be due to jet–cloud interactions, are within ∼−250 km s−1 and do not appear to extend to values over 1000 km s−1 seen for the more luminous objects. This could be due to the weaker jets in these objects, but requires confirmation from observations of a larger sample of sources. There appears to be no evidence of any dependence of H i column density on either luminosity or redshift, but these new detections are consistent with the inverse relation between H i column density and projected linear size.