Low-power radio galaxy environments in the Subaru/XMM-Newton Deep Field at z~0.5

TL;DR

This study investigates the environments of low-power radio galaxies at z~0.5, revealing they reside in moderately rich groups with X-ray properties similar across systems, and suggests galaxy interactions influence radio galaxy activity.

Contribution

It provides the first detailed spectroscopic and X-ray analysis of low-power radio galaxy environments at intermediate redshift, highlighting the role of group interactions in triggering radio activity.

Findings

Radio galaxies are in moderately rich groups with similar X-ray properties.

A low-power radio galaxy is triggered within a subgroup interacting with another group.

Galaxy interactions during group mergers may influence radio galaxy life cycles.

Abstract

We present multi-object spectroscopy of galaxies in the immediate (Mpc-scale) environments of four low-power (L_1.4 GHz < 10^25 W/Hz) radio galaxies at z~0.5, selected from the Subaru/XMM-Newton Deep Field. We use the spectra to calculate velocity dispersions and central redshifts of the groups the radio galaxies inhabit, and combined with XMM-Newton (0.3-10 keV) X-ray observations investigate the L_X--sigma_v and T_X--sigma_v scaling relationships. All the radio galaxies reside in moderately rich groups -- intermediate environments between poor groups and rich clusters, with remarkably similar X-ray properties. We concentrate our discussion on our best statistical example that we interpret as a low-power (FRI) source triggered within a sub-group, which in turn is interacting with a nearby group of galaxies, containing the bulk of the X-ray emission for the system -- a basic scenario which can be compared to more powerful radio sources at both high (z>4) and low (z<0.1) redshifts. This suggests that galaxy-galaxy interactions triggered by group mergers may play an important role in the life-cycle of radio galaxies at all epochs and luminosities.