The Environments of Low and High Luminosity Radio Galaxies at Moderate Redshifts

TL;DR

This study uses spectroscopy to examine whether the environment influences radio galaxy luminosity at moderate redshifts, finding no significant correlation and suggesting radio galaxies are not reliable indicators of group environments at these distances.

Contribution

It provides the first spectroscopic investigation into the environment-luminosity relationship of radio galaxies at z ~ 0.3, clarifying previous photometric ambiguities.

Findings

No correlation between radio luminosity and environment at z ~ 0.3.

Radio galaxies are not effective tracers of group environments at moderate redshifts.

Spectroscopic data confirms photometric analysis results.

Abstract

In the local Universe, high-power radio galaxies live in lower density environments than low-luminosity radio galaxies. If this trend continues to higher redshifts, powerful radio galaxies would serve as efficient probes of moderate redshift groups and poor clusters. Photometric studies of radio galaxies at 0.3 < z < 0.5 suggest that the radio luminosity-environment correlation disappears at moderate redshifts, though this could be the result of foreground/background contamination affecting the photometric measures of environment. We have obtained multi-object spectroscopy of in the fields of 14 lower luminosity (L_1.4GHz < 4x10^24 W/Hz) and higher luminosity (L_1.4GHz > 1.2x10^25 W/Hz) radio galaxies at z ~ 0.3 to spectroscopically investigate the link between the environment and the radio luminosity of radio galaxies at moderate redshifts. Our results support the photometric analyses; there does not appear to be a correlation between the luminosity of a radio galaxy and its environment at moderate redshifts. Hence, radio galaxies are not efficient signposts for group environments at moderate redshifts.