THE OPTICAL LUMINOSITY FUNCTION OF VOID GALAXIES IN THE SDSS AND ALFALFA SURVEYS

We measure the r-band galaxy luminosity function (LF) across environments over the redshift range 0 < z < 0.107 using the Sloan Digital Sky Survey (SDSS). We divide our sample into galaxies residing in large-scale voids (void galaxies) and those residing in denser regions (wall galaxies). The best-fitting Schechter parameters for void galaxies are log Phi* = -3.40 +/- 0.03 log(Mpc(-3)), M* = -19.88 +/- 0.05, and alpha = -1.20 +/- 0.02. For wall galaxies, the best-fitting parameters are log Phi* = -2.86 +/- 0.02 log(Mpc(-3)), M* = -20.80 +/- 0.03, and alpha = -1.16 +/- 0.01. We find a shift in the characteristic magnitude, M*, toward fainter magnitudes for void galaxies and find no significant difference between the faint-end slopes of the void and wall galaxy LFs. We investigate how low-surface-brightness selection effects can affect the galaxy LF. To attempt to examine a sample of galaxies that is relatively free of surface-brightness selection effects, we compute the optical galaxy LF of galaxies detected by the blind H I survey Arecibo Legacy Fast ALFA (ALFALFA). We find that the global LF of the ALFALFA sample is not well fit by a Schechter function because of the presence of a wide dip in the LF around M-r = -18 and an upturn at fainter magnitudes (alpha similar to -1.47). We compare the H I selected r-band LF to various LFs of optically selected populations to determine where the H I selected optical LF obtains its shape. We find that sample selection plays a large role in determining the shape of the LF.