SIMBAD references

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.