| Voids in the large-scale structure of the universe offer a window into the relationship between global environment and local structure formation. I investigate the properties of galaxies within voids and the incidence of Lyman-alpha absorption systems as a function of density.; Many low-redshift (z < 0.05) Lyman-alpha absorbers seen by Hubble Space Telescope are within the region covered by the Center for Astrophysics Redshift Survey (CfA2), allowing a study of the correlation between absorber locations and the large-scale structure defined by galaxies. I construct a galaxy number density estimator from CfA2 smoothed on a 5 h-1 Mpc scale and determine the distribution of surrounding densities for 18 of the nearby Lyman-alpha absorbers. The absorbers are uncorrelated with the local large-scale structure, i.e. their density distribution is consistent with randomly-selected locations within the survey and inconsistent with the environments of CfA2 galaxies. As predicted by recent cosmological simulations, Lyman-alpha absorbers do not avoid the voids.; With a multicolor imaging and spectroscopic survey of 300 galaxies in and around three prominent voids within CfA2, I investigate the H-alpha linewidths and the luminosity, color, and morphological distributions of galaxies in low-density regions. The properties of galaxies in regions below half the CfA2 mean density differ significantly from those at larger densities: they have bluer colors, more late-type morphologies, stronger H-alpha emission, and a steeper luminosity function. I also use the imaging survey fields to make a deeper redshift survey (r ≤ 16.1) around each galaxy. The incidence of nearby companions is insensitive to the global density, but neighboring galaxies have smaller velocity separation in the lowest-density regions, possibly important for triggering star formation in gas-rich void galaxies. |
