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

We study the optical properties of a large sample of galaxies in low-densityregions of the nearby universe. We make a 5/h Mpc-smoothed map of the galaxydensity throughout the Center for Astrophysics Redshift Survey (CfA2) toidentify galaxies within three prominent nearby ``voids'' with diameter >30/hMpc. We augment the CfA2 void galaxy sample with fainter galaxies found in thesame regions from the deeper Century and 15R Redshift Surveys. We obtain B andR CCD images and high-S/N longslit spectra for the resulting sample of 149 voidgalaxies, and also for 131 galaxies on the periphery of these voids. Here we describe the photometry for the sample, including B isophotalmagnitudes and B-R colors. For the 149 galaxies which lie in regions below themean survey density, the luminosity functions in B and R are well-fit bySchechter functions with respective parameters (alpha_B = -0.5 +/- 0.3, B_* =-18.9 +/- 0.2) and (alpha_R = -0.9 +/- 0.3, R_* = -20.4 +/- 0.3). The Bluminosity function (LF) is consistent with typical survey LFs (e.g., theSouthern Sky Redshift Survey), and the R LF is consistent with the CenturySurvey. The B and R LFs of 131 galaxies in the ``void periphery'', regionsbetween the mean density and twice the mean, have similar Schechter parameters.The CfA2 LF is inconsistent with both samples at 3.5-sigma. When we narrow our analysis to the 46 galaxies in regions below half the meandensity, the LF is steeper: alpha = -1.4 +/- 0.5. The typical survey LFs areinconsistent with this subsample at 2-sigma. The B-R color distribution ofgalaxies in the lowest-density regions is also shifted significantly (3-sigma)blue-ward of the higher density samples. The most luminous red galaxies (R <-21) are absent from the lowest density regions at 2.5-sigma.Comment: 33 pages, 16 figures; AJ in press (Dec. 1999); Version with full-resolution figures available from ftp://ftp.stsci.edu/outside-access/out.going/nagrogin/Grogin1.tar.g