Photometric Properties of Void Galaxies in the Sloan Digital Sky Survey

Using a nearest neighbor analysis, we construct a sample of void galaxies from the Sloan Digital Sky Survey (SDSS) and compare the photometric properties of these galaxies to the population of non-void (wall) galaxies. We trace the density field of galaxies using a volume-limited sample with zmax = 0.089. Galaxies from the flux-limited SDSS with z ≤ zmax and fewer than three volume-limited neighbors within 7hMpc are classified as void galaxies. This criterion implies a density contrast δρ/ρ < −0.6 around void galaxies. From 155,000 galaxies, we obtain a sub-sample of 13,742 galaxies with z ≤ zmax, from which we identify 1,010 galaxies as void galaxies. To identify an additional 194 faint void galaxies from the SDSS in the nearby universe, r ∼< 72h Mpc, we employ volume-limited samples extracted from the Updated Zwicky Catalog and the Southern Sky Redshift Survey with zmax = 0.025 to trace the galaxy distribution. Our void galaxies span a range of absolute magnitude from Mr = −13.5 to Mr = −22.5. Using SDSS photometry, we compare the colors, concentration indices, and Sersic indices of the void and wall samples. Void galaxies are significantly bluer than galaxies lying at higher density. The population of void galaxies with Mr ∼< M ∗ + 1 and brighter is on average bluer and more concentrated (later type) than galaxies outside of voids. The latter behavior is only partly explained by the paucity of luminous red galaxies in voids. These results generally agree with the predictions of semi-analytic models for galaxy formation in cold dark matter models, which indicate that void galaxies should be relatively bluer, more disklike, and have higher specific star formation rates. Subject headings: cosmology: observations — large-scale structure of universe — methods: statistical — galaxies: photometry — galaxies: structure Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059