Spectral Properties of Galaxies in Void Regions
  We present a study of spectral properties of galaxies in underdense
large-scale structures, voids. Our void galaxy sample (75,939 galaxies) is
selected from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) with
$\rm z < 0.107$. We find that there are no significant differences in the
luminosities, stellar masses, stellar populations, and specific star formation
rates between void galaxies of specific spectral types and their wall
counterparts. However, the fraction of star-forming galaxies in voids is
significantly higher ($\ge 9\%$) than that in walls. Void galaxies, when
considering all spectral types, are slightly fainter, less massive, have
younger stellar populations and of higher specific star formation rates than
wall galaxies. These minor differences are totally caused by the higher
fraction of star-forming galaxies in voids. We confirm that AGNs exist in
voids, already found by \cite{co08}, with similar abundance as in walls. Type I
AGNs contribute $\sim$ 1\%-2\% of void galaxies, similar to their fraction in
walls. The intrinsic [O III] luminosities , spanning over $10^6\ L_{\sun} \sim
10^9\ L_{\sun}$, and Eddington ratios are similar comparing our void AGNs
versus wall AGNs. Small scale statistics show that all spectral types of void
galaxies are less clustered than their counterparts in walls. Major merger may
not be the dominant trigger of black hole accretion in the luminosity range we
probe. Our study implies that the growth of black holes relies weakly on large
scale structures.
