THE ENVIRONMENTS OF LOW- AND HIGH-LUMINOSITY RADIO GALAXIES AT MODERATE REDSHIFTS

Abstract

In the local universe, high-power radio galaxies live in lower-density environments than low-luminosity radio galaxies. If this trend continued 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 (L1.4 GHz < 4 × 1024 W Hz−1) and higher luminosity (L1.4 GHz > 1.2 × 1025 W Hz−1) 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.