HI absorption towards nearby compact radio sources

TL;DR

This study measures HI absorption in nearby compact radio sources, finding similar detection rates to more luminous sources and exploring the influence of luminosity and size on HI features.

Contribution

First systematic HI absorption measurements towards lower luminosity CSS and GPS sources, expanding understanding of their gas properties.

Findings

Detection rate similar to more luminous sources

Higher detection rate in GPS compared to CSS objects

No clear dependence of HI column density on luminosity or redshift

Abstract

We present the results of HI absorption measurements towards a sample of nearby Compact Steep-Spectrum (CSS) and Giga-Hertz Peaked Spectrum (GPS) radio sources, the CORALZ sample, using the Giant Metrewave Radio Telescope (GMRT). We observed a sample of 18 sources and find 7 new detections. These sources are of lower luminosity than earlier studies of CSS and GPS objects and we investigate any dependence of HI 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 $\sim$$-$250 km s$^{-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 HI column density on either luminosity or redshift, but these new detections are consistent with the inverse relation between HI column density and projected linear size.