The environment of C- and S-shaped radio galaxies

Abstract

We study the environment of radio galaxies with different morphological types using the Proctor sample, which was built from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey archive. Among the 15 radio galaxy types classified by Proctor, 199 C-shaped (i.e., wide- or narrow-angle tail) and 203 S-shaped (i.e., S- or Z-shaped) sources are selected in this work, which are located in the redshift range of 0.02 < z < 1, because these two subsamples are relatively larger than the other subsamples in the Proctor sample. By cross-matching these radio galaxies with the optical sources drawn from the Sloan Digital Sky Survey (SDSS) database and counting the SDSS sources with an r-band absolute magnitude brighter than −19 located within a 0.5 Mpc distance around each source (i.e., the richness), we find that the fraction of C-shaped sources with a richness above 10 is larger than that of S-shaped sources. We have also correlated the radio galaxies in our sample with the brightest cluster galaxies (BCGs) defined in the NASA/IPAC Extragalactic Database (NED), and infer that the C-shaped sources are more likely to be BCGs than the S-shaped sources. These results support the idea that C-shaped radio galaxies often reside in a richer environment than radio galaxies with other morphological types.