We constrain the assembly history of galaxies in the central 0.6 Mpc of the rich Coma cluster at z~0.02 based on the structure of 69 massive (M*>1e9 M_sun) galaxies using images from the HST Treasury Survey of Coma. Our findings are: (1) We make no a priori assumptions on the shape of the profile for outer and central structures, which can include disk-dominated components, bars, and classical bulges/ellipticals. After excluding the 2 cDs, we find that most (56%) of the galactic stellar mass resides in classical bulges/Es while (44%) resides in cold disk-dominated structures. This suggests that most of the stellar mass in Coma galaxies may have been assembled and shaped through the redistribution of stars during major mergers, and possibly minor mergers, but that gas-rich dissipative processes that build disk-dominated structures remain important even in the center of a rich cluster like Coma. (2) We see strong evidence of a morphology-density relation. In the central 0.6 Mpc of the Coma cluster, there are 2 cDs, spirals are rare, and the morphology breakdown of (E+S0):spirals is (22.4% + 70.2%):7.4% by numbers and (28.1% + 66.2%):5.7% by stellar mass. (3) In agreement with earlier work, we find that at a given galaxy stellar mass, the average half-light radius of the outer disk in S0s/spirals is ~40-80% smaller and the average outer disk i-band luminosity is fainter by ~42-70% in Coma than in lower-density environments. These properties are likely indicative of environmental processes. (4) We compare our empirical results with predictions from a hierarchical semi-analytic model. No single cluster model can simultaneously match all the global properties (number density, mass function, halo properties) of the Coma cluster. Our study of Coma underscores that galaxy evolution is not solely a function of stellar mass, but also environment.
Date added: Tue, 15 Oct 13