The luminosity function of void galaxies in the Sloan Digital Sky Survey

We measure the r-band luminosity function (LF) of a sample of 10(3) void galaxies over a large range of magnitude, -21.5< M-r< - 14.5. These objects were identified by Rojas et al. from the Sloan Digital Sky Survey as residing in regions with local galaxy density δρ/ρ < -0.6 on a scale of 7 h(-1) Mpc. We compare the void galaxy LF with that of galaxies in denser regions (so-called wall'' galaxies). The void galaxy LF is well fitted by a Schechter function with normalization Phi* = (0.19 +/- 0.04) x 10(-2) h(3) Mpc(-3), characteristic magnitude M-r*- 5 log h = - 19.74 +/- 0.11, and faint-end slope alpha = - 1.18 +/- 0.13. A comparable measurement of the LF of wall galaxies yields Phi* = (1.42 +/- 0.03) x 10(-2) h(3) Mpc(-3), M-r* - 5 log h = - 20.62 +/- 0.08, and alpha = -1.19 +/- 0.07. Thus, we find that void galaxies are characteristically fainter than wall galaxies, but we do not find a significant dependence of the slope of the LF at the faint end on environment alone. The latter result suggests that there is no excess of dwarfs in voids, in contrast to predictions of cold dark matter (CDM) models. We split both the void and wall samples in half by density and find that the LFs of both the higher and lower density void galaxies and the lower density wall galaxies are similar in shape. However, the LF of wall galaxies in the highest density regions has a shallower faint-end slope, i.e., there are relatively fewer faint galaxies in the highest density regions. The LF of void galaxies is most similar to that of late-type galaxies in denser regions. The LFs of subsamples of wall galaxies that have blue g - r color, spiral-like surface brightness profiles (Sersic index n < 2), or relatively high star formation rates [EW(Hα)> 5 Angstrom], have brighter M-r* but faint-end slopes similar to those of void galaxies. In contrast, the LFs of wall galaxies with red g - r color, elliptical-like profiles, or low star formation rates have significantly shallower faint-end slopes and brighter values of M-r* than we find for void galaxies. We conclude that the void galaxy population is dominated by faint, late-type galaxies. The shift in M* between the void and wall galaxy LFs is consistent with the shift of the mass function in voids predicted by extended Press-Schechter theory.