Spectroscopic Properties of Void Galaxies in the Sloan Digital Sky Survey

We study the spectroscopic properties of a sample of 10³ void galaxies identified in 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 δρ/ρ < -0.6. We compare the equivalent widths of Hα, [O II], [N II], Hβ, and [O III] of void and wall galaxies with similar luminosities. We find that void galaxies have larger emission line equivalent widths, indicating that they are forming stars at a higher rate. A comparison of the Balmer break, as measured by the parameter D_n(4000), reveals that void galaxies have younger stellar populations than wall galaxies. Using standard techniques, we estimate Hα and [O II] star formation rates (SFRs) of the void and wall galaxies. Combining these measurements with estimates of the stellar masses, we find specific star formation rates (SFR per unit stellar mass) for void galaxies that are generally higher than for wall galaxies, consistent with the results from the equivalent widths.