An Imaging and Spectroscopic Survey of Galaxies within Prominent Nearby Voids. I. The Sample and Luminosity Distribution

Abstract

We study the optical properties of a large sample of galaxies in low-density regions of the nearby universe. We make a 5 h-1 Mpc smoothed map of the galaxy density throughout the Center for Astrophysics Redshift Survey (CfA2) to identify galaxies within three prominent nearby voids with diameter 30 h-1 Mpc. We augment the CfA2 galaxy sample with fainter galaxies found in the same regions from the more recent and deeper Century and Redshift surveys . We obtain B and R CCD images and high signal-to-noise long-slit spectra for the resulting sample of 149 galaxies, as well as for an additional 131 galaxies on the periphery of these voids. Here we describe the photometry for the sample, including B isophotal magnitudes and B-R colors. For the 149 galaxies that lie in regions below the mean survey density, the luminosity functions in B and R are well fit by Schechter functions with respective parameters (αB = -0.5 ± 0.3, B* = -18.9 ± 0.2) and (αR = -0.9 ± 0.3, R* = -20.4 ± 0.3). The B luminosity function (LF) is consistent with typical survey LFs (e.g., the Southern Sky Redshift Survey), and the R LF is consistent with the Century Survey. The B and R LFs of 131 galaxies in the void periphery—regions between the mean density and twice the mean—have similar Schechter parameters. The CfA2 LF is inconsistent with both samples at the 3.5 σ level. When we narrow our analysis to the 46 galaxies in regions below half the mean density, the LF is significantly steeper: α ~ -1.4 ± 0.5. The typical survey LFs are inconsistent with this subsample at the ~2 σ level. The B-R color distribution of galaxies in the lowest density regions is also shifted significantly (~3 σ) blueward of the higher density samples. The most luminous red galaxies (R -21) are absent from the lowest density regions at the 2.5 σ level.