Spectroscopic Properties of Void Galaxies in the Sloan Digital Sky   Survey
  We study the spectroscopic properties of a sample of 10^3 void galaxies from the Sloan Digital Sky Survey (SDSS) and compare these with the properties of galaxies in higher density regions (wall galaxies). This sample of void galaxies covers the range of absolute magnitude from M_r=-13.5 to M_r=-22.5 in regions with density contrast delta < -0.6. In this paper we compare the equivalent widths of Halpha, [OII], [NII], Hbeta, and [OIII] of void and wall galaxies of similar luminosities and find that void galaxies have larger values, indicating that they are still forming stars at a high rate. A comparison of the Balmer break, as measured by the parameter Dn(4000), reveals that void galaxies have younger stellar populations than wall galaxies. Using standard techniques, we estimate Halpha and [OII] star formation rates of the void and wall galaxies and along with estimates of the stellar masses, we compute specific star formation rates. In most cases, we find that void galaxies have similar SFRs to wall galaxies but they are fainter and smaller mass. This means that, consistent with the EWs, void galaxies have higher specific star formation rates than wall galaxies. 
Randall R. Rojas, Michael S. Vogeley, Fiona Hoyle (Drexel), Jon   Brinkmann (APO)