2004ApJ...617...50R

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 nonvoid (wall) galaxies. We trace the density field of galaxies using a volume-limited sample with z_max=0.089. Galaxies from the flux-limited SDSS with z≤z_maxand fewer than three volume-limited neighbors within 7 h^–1 Mpc 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 subsample of 13,742 galaxies with z≤z_max, from which we identify 1010 galaxies as void galaxies. To identify an additional 194 faint void galaxies from the SDSS in the nearby universe, r≲72h^–1Mpc, we employ volume-limited samples extracted from the Updated Zwicky Catalog and the Southern Sky Redshift Survey with z_max=0.025 to trace the galaxy distribution. Our void galaxies span a range of absolute magnitude from M_r=-13.5 to -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 M_r≲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 semianalytic 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.