The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three‐dimensional Structure of the Virgo Cluster

Abstract

The ACS Virgo Cluster Survey consists of HST ACS imaging for 100 early-type\ngalaxies in the Virgo Cluster, observed in the F475W and F850LP filters. We\nderive distances for 84 of these galaxies using the method of surface\nbrightness fluctuations (SBFs), present the SBF distance catalog, and use this\ndatabase to examine the three-dimensional distribution of early-type galaxies\nin the Virgo Cluster. The SBF distance moduli have a mean (random) measurement\nerror of 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBF\nmeasurements for Virgo Cluster galaxies. Five galaxies lie at a distance of ~23\nMpc and are members of the W' cloud. The remaining 79 galaxies have a narrow\ndistribution around our adopted mean distance of 16.5+/-0.1 (random mean error)\n+/-1.1 Mpc (systematic). The rms distance scatter of this sample is 0.6+/-0.1\nMpc, with little dependence on morphological type or luminosity class (i.e.,\n0.7+/-0.1 and 0.5+/-0.1 Mpc for the giants and dwarfs, respectively). The\nback-to-front depth of the cluster measured from our sample of galaxies is\n2.4+/-0.4 Mpc (i.e., +/-2sigma of the intrinsic distance distribution). The M87\n(cluster A) and M49 (cluster B) subclusters are found to lie at distances of\n16.7+/-0.2 and 16.4+/-0.2 Mpc, respectively. There may be a third subcluster\nassociated with M86. A weak correlation between velocity and line-of-sight\ndistance may be a faint echo of the cluster velocity distribution not having\nyet completely virialized. In three dimensions, Virgo's early-type galaxies\nappear to define a slightly triaxial distribution, with axis ratios of\n(1:0.7:0.5). The principal axis of the best-fit ellipsoid is inclined ~20-40\ndeg. from the line of sight, while the galaxies belonging to the W' cloud lie\non an axis inclined by ~10-15 deg.\n