Spectral Properties of Galaxies in Void Regions

TL;DR

This study analyzes the spectral properties of galaxies in voids compared to walls, finding minimal differences in intrinsic properties but a higher fraction of star-forming galaxies in voids, with black hole growth weakly dependent on large-scale structures.

Contribution

It provides a comprehensive comparison of spectral properties of void and wall galaxies using SDSS data, highlighting the higher star-forming fraction in voids and the similar AGN characteristics across environments.

Findings

Void galaxies have a higher fraction of star-forming types.

Intrinsic properties of galaxies are similar in voids and walls.

AGN properties are consistent across environments.

Abstract

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.