The Complete Local Volume Groups Sample - II. A study of the Central Radio Galaxies in the High$-$Richness Sub-sample

TL;DR

This study investigates the radio properties of dominant early-type galaxies in galaxy groups, revealing high detection rates, diverse radio morphologies, and insights into AGN feedback mechanisms in different X-ray environments.

Contribution

It provides a comprehensive analysis of radio emissions in galaxy groups, combining new GMRT observations with archival data, highlighting the prevalence and characteristics of radio sources in these environments.

Findings

92% of dominant galaxies host radio sources

Radio sources range from point-like to diffuse with varied spectra

Jet activity correlates with X-ray brightness of groups

Abstract

We present a study of the radio properties of the dominant early-type galaxies in 26 galaxy groups, the high-richness sub-sample of the Complete Local-volume Groups Sample (CLoGS). Combining new 610 MHz and 235 MHz observations of 21 groups from the Giant Metrewave Radio Telescope (GMRT) with archival GMRT and Very Large Array (VLA) survey data, we find a high detection rate, with 92% of the dominant galaxies hosting radio sources. The sources have a wide range of luminosities, 10$^{20}$ $-$ 10$^{24}$ W/Hz in the 235 and 610 MHz bands. The majority (54%) are point-like, but 23% have radio jets, and another 15% are diffuse radio sources with no clear jet/lobe morphology. The spectral index of the detected radio sources ranges from very flat values of ~0.2 to typical radio synchrotron spectra of ~0.9 with only two presenting steep radio spectra with $\alpha_{235}^{610}$ > 1. We find that jet sources are more common in X-ray bright groups, with radio non-detections found only in X-ray faint systems. Radio point sources appear in all group environments irrespective of their X-ray properties or spiral fraction. We estimate the mechanical power (Pcav) of the jet sources in the X-ray bright groups to be 10$^{41}$ $-$ 10$^{43}$ erg/s, with the two large-scale jet systems (NGC 193 and NGC 4261) showing jet powers two orders of magnitude greater than the radiative losses from the cool cores of their groups. This suggests that central AGN are not always in balance with cooling, but may instead produce powerful periodical bursts of feedback heating.