Imprints of Environment on Cluster and Field Late - Type Galaxies at Z ∼ 1

We present a comparison of late-type galaxies (Sa and later) in intermediate redshift clusters and the field using images from the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). Cluster and field galaxies are selected by matching photometric and spectroscopic catalogs of four cluster fields: CL0152-1357, CL1056-0337 (MS1054), CL1604+4304, and CL1604+4321. Concentration , asymmetry, and clumpiness parameters are calculated for each galaxy in blue (F606W or F625W) and red (F775W or F814W) filters. Galaxy half-light radii, disk scale lengths, color gradients, and overall color are compared. We find marginally significant differences in the asymmetry distributions of spiral and irregular galaxies in the X-ray luminous and X-ray faint clusters. The massive clusters contain fewer galaxies with large asymmetries. The physical sizes of the cluster and field populations are similar; no significant differences are found in half-light radii or disk scale lengths. The most significant difference is in rest-frame U − B color. Late-type cluster galaxies are significantly redder, ∼ 0.3 magnitudes at rest-frame U − B, than their field counterparts. Moreover, the intermediate-redshift cluster galaxies tend to have blue inward color gradients, in contrast to the field galaxies, but similar to late-type galaxies in low redshift clusters. These blue inward color gradients are likely to be the result of enhanced nuclear star formation rates relative to the outer disk. Based on the significant rest-frame color difference, we conclude that late-type cluster members at z ∼ 0.9 are not a pristine infalling field population; some difference in past and/or current star formation history is already present. This points to high redshift " groups " , or filaments with densities similar to present-day groups, as the sites where the first major effects of environment are imprinted. Understanding the physical processes that shape present day galaxies is one of modern astronomy's fundamental goals. Galaxy morphology is clearly related to environment (Dressler 1980; Postman & Geller 1984; Whitmore & Gilmore 1991). Few gas-rich galaxies and relatedly, few galaxies with spiral morphologies are found in the cores of rich clusters. To what extent the environment drives galaxy evolution (nurture) or is simply a roadmap for the distribution of galaxy halo masses (nature) is being currently refined. By observing clusters at high redshift we can directly observe dynamically young structures. There is substantial evidence that overall cluster galaxy populations evolve with redshift. Fractionally more blue galaxies are found in clusters at higher redshifts; this …