Dwarf Galaxies in Voids: Luminosity, Gas, and Star Formation Properties

We examine the first statistically-significant sample of dwarf galaxies in voids with matched optical (Sloan Digital Sky Survey), radio (Arecibo Legacy Fast ALFA Survey), and UV (GALEX) observations, which allows us to probe the impact of voids on the luminosity function, HI mass function, and star formation history of galaxies. Large-scale voids provide a unique environment for studying galaxy formation and evolution. Previous theoretical work predicts that galaxies residing in large-scale voids evolve as if they were in a universe with lower matter density, higher dark energy density, and larger Hubble constant. Environmental processes such as ram pressure stripping and galaxy-galaxy interactions should be less important for void galaxies than for galaxies in denser regions (wall galaxies). We measure the effects of environment on two fundamental tests of galaxy formation: the galaxy luminosity function (LF) and the HI mass function (HIMF). In both cases, we find a significant shift towards lower-mass, fainter galaxies in voids. However, we do not detect a dependence on environment of the low-mass/faint end slope of the HIMF and LF. We find that including low surface brightness dwarf galaxies from a blind HI survey steepens the r-band LF substantially, but not enough to reconcile the mismatch predicted low-mass slope of the dark matter halo mass function and the faint-end slope of the observed luminosity function. Utilizing optical, HI, and UV information of nearby galaxies, we determine that specific star formation rates of dwarf galaxies down to Mr= --13 are higher in voids than in walls. Furthermore, we downsample the ALFALFA wall galaxy distribution so that its stellar mass distribution matches the stellar mass distribution of void galaxies and determine the environmental dependence of star formation efficiency. We do not find strong evidence that star formation efficiency is dependent on large-scale environment, but this result is likely dependent on the requirements that all galaxies, regardless of environment, have high HI signal-to-noise flux and similar stellar mass distributions.