The HST/ACS Coma Cluster Survey - VII. Structure and Assembly of Massive
  Galaxies in the Center of the Coma Cluster
  We constrain the assembly history of galaxies in the projected central 0.5
Mpc of the Coma cluster by performing structural decomposition on 69 massive
(M_star >= 10^9 M_sun) galaxies using high-resolution F814W images from the HST
Treasury Survey of Coma. Each galaxy is modeled with up to three Sersic
components having a free Sersic index n. After excluding the two cDs in the
projected central 0.5 Mpc of Coma, 57% of the galactic stellar mass in the
projected central 0.5 Mpc of Coma resides in classical bulges/ellipticals while
43% resides in cold disk-dominated structures. Most of the stellar mass in Coma
may have been assembled through major (and possibly minor) mergers. Hubble
types are assigned based on the decompositions, and we find a strong
morphology-density relation; the ratio of (E+S0):spirals is (91.0%):9.0%. In
agreement with earlier work, the size of outer disks in Coma S0s/spirals is
smaller compared with lower-density environments captured with SDSS (Data
Release 2). Among similar-mass clusters from a hierarchical semi-analytic
model, no single cluster can simultaneously match all the global properties of
the Coma cluster. The model strongly overpredicts the mass of cold gas and
underpredicts the mean fraction of stellar mass locked in hot components over a
wide range of galaxy masses. We suggest that these disagreements with the model
result from missing cluster physics (e.g., ram-pressure stripping), and certain
bulge assembly modes (e.g., mergers of clumps). Overall, our study of Coma
underscores that galaxy evolution is not solely a function of stellar mass, but
also of environment.
