From Cluster Core to Splashback: Linking Dynamical Structure to Multidimensional Galaxy Evolution in the Coma Cluster

The study investigates how galaxy evolution varies across the full dynamical structure of the Coma cluster, using the GalWCat19 spectroscopic cluster catalog combined with SDSS-based value-added galaxy properties. The authors measure a splashback radius of R_sp = 2.94 ± 0.16 h^-1 Mpc, and use specific star formation rate (sSFR), color offset from the red sequence (Δ(g-r)_RS), and bulge-to-total ratio (B/T) as independent diagnostics.

They find a coherent environmental transition: galaxies in the cluster core are quiescent, red, and bulge-dominated, while populations at larger radii are increasingly star-forming, blue, and disk-dominated. A new three-dimensional framework in the joint (log sSFR, Δ(g-r)_RS, B/T) space uses a peak-based classification scheme that extends beyond traditional one-dimensional galaxy classifications. This identifies two dominant populations: red, quiescent, bulge-dominated galaxies (51% of the joint-analysis sample) and blue, star-forming, disk-dominated galaxies (29%). The remaining ~20% occupy transitional or mixed states connecting these two principal populations.

The relative fractions shift strongly near the splashback radius: the red, quiescent, bulge-dominated population declines rapidly while the blue, star-forming, disk-dominated population becomes increasingly dominant. This indicates that the splashback boundary is not only a dynamical boundary but also a critical evolutionary transition zone. Overall, the findings suggest that galaxy evolution in Coma proceeds through continuous multidimensional pathways—star formation quenching, color evolution, and morphological transformation occur on different timescales but remain closely linked to the cluster's dynamical structure.