Tracing X-ray and HI absorption in peaked spectrum sources

TL;DR

This study investigates the potential correlation between X-ray and HI absorption in a broad radio galaxy population, highlighting current limitations due to selection bias and discussing future prospects with upcoming data.

Contribution

It analyzes a large historic sample to assess the correlation between X-ray and HI absorption across diverse radio sources, extending beyond peaked spectrum sources.

Findings

Some evidence for correlation outside peaked spectrum sources

Selection bias limits current analysis

Future data from the SEAFOG project will enhance understanding

Abstract

Recent studies have shown that both 21cm HI absorption and soft X-ray absorption serve as excellent tracers of the dense and dusty gas near the active nucleus of young radio galaxies, offering new insight into the physical nature of the circumnuclear medium. To date, a correlation between the column densities derived using these absorption processes has been observed within Compact Steep Spectrum (CSS) and Gigahertz-Peaked Spectrum (GPS) radio sources. While it is possible that this correlation exists within the broader radio population, many samples of radio galaxies make this difficult to test due to selection effects. This paper explores the possibility of a correlation in the broader radio population by analysing a historic sample of 168 radio sources compiled from the literature in such a way so as to minimise selection bias. From this historic sample we conclude that there is some evidence for a correlation between HI and soft X-ray absorption outside of peaked spectrum sources, but that the selection bias towards these sources makes further analysis difficult using current samples. We discuss this in the context of the SEAFOG project and how forthcoming data will change the landscape of future absorption studies.