Outskirts of Galaxy Clusters A1139, A1314, A1656, A2040, A 2052, A2107: Star-Formation Rate

Abstract

We investigate the variation of the fraction of galaxies with suppressed star formation (M_K < −21_.^m5) and early-type galaxies (frac_E) of the “red sequence” along the projected radius in six galaxy clusters:Coma (A1656), A1139, and A1314 in the Leo supercluster region (z ≈ 0.037) and A2040, A2052, A2107 in the Hercules supercluster region (z ≈ 0.036). According to SDSS (DR10) data, frac_E is the highest in the central regions of galaxy clusters and it is, on the average, equal to 0.62 ± 0.03, whereas in the 2–3R/R_200c interval and beyond the R_sp ≈ 0.95 ± 0.04 R_200m radius that we inferred from the observed profile frac_E is minimal and equal to 0.25 ± 0.02. This value coincides with the estimate frac_E = 0.24 ± 0.01 that we inferred for field galaxies located between the Hercules and Leo superclusters at the same redshifts. We show that the fraction of galaxies with suppressed star formation decreases continuously with cluster radius from 0.87 ± 0.02 in central regions down to 0.43 ± 0.03 in the 2–3 R/R_200c interval and beyond R_sp, but remains, on the average, higher than 26% than the corresponding fraction for field objects. This decrease is especially conspicuous in the galaxy mass interval log M_* [M_⊙] = 9.5–10. We found that galaxies with ongoing star formation have average clustercentric distances 1.5–2.5 R/R_200c and that their radial-velocity dispersions are higher than those of galaxies with suppressed star formation.