Imprints of Environment on Cluster and Field Late-type Galaxies

We present a comparison of late-type galaxies (Sa and later) in intermediate-redshift clusters and in the field using images from the Advanced Camera for Surveys aboard the Hubble Space Telescope. Cluster and field galaxies are selected by matching photometric and spectroscopic catalogs of four cluster fields: Cl 0152 1357, Cl 1056 0337 (MS 1054), Cl 1604+4304, and Cl 1604+4321. Concentration, asymmetry, and clumpiness parameters are calculated for each galaxy in blue (F606Wor F625W) and red (F775Wor 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 mag 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.