Clustering of galaxies around radio quasars at 0.5≤z≤0.8

We have observed the galaxy environments around a sample of 21 radio-loud, steep-spectrum quasars at 0.5≤ z ≤0.82, spanning several orders of magnitude in radio luminosity. The observations also include background control fields used to obtain the excess number of galaxies in each quasar field. The galaxy excess was quantified using the spatial galaxy–quasar correlation amplitude, B _gq, and an Abell-type measurement, N _0.5. A few quasars are found in relatively rich clusters, but on average, they seem to prefer galaxy groups or clusters of approximately Abell class 0. We have combined our sample with literature samples extending down to z ≈0.2 and covering the same range in radio luminosity. By using the Spearman statistic to disentangle redshift and luminosity dependences, we detect a weak, but significant, positive correlation between the richness of the quasar environment and the radio luminosity of the quasar. However, we do not find any epoch dependence in B _gq, as has previously been reported for radio quasars and galaxies. We discuss the radio luminosity–cluster richness link and possible explanations for the weak correlation that is seen.