SPECTRAL PROPERTIES OF GALAXIES IN VOID REGIONS

We present a study of spectral properties of galaxiesin underdense large-scale structures, voids. Our void galaxysample (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 galaxiesof specific spectral types and their wall counterparts. However, the fraction of star-forming galaxiesin voidsis significantly higher ($\ge 9\%$) than that in walls. Void galaxies, when considering all spectral types, are slightly fainter, less massive, have younger stellar populationsand of higher specific star formation rates than wall galaxies. These minor differences are totally caused by the higher fraction of star-forming galaxiesin 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 voidAGNs versus wall AGNs. Small scale statistics show that all spectral types of void galaxiesare 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.