The impact of void environment on AGN

TL;DR

This study investigates how the void environment influences active galactic nuclei (AGN) characteristics, revealing higher AGN activity and massive black hole accretion in voids compared to denser regions, using optical and mid-IR data.

Contribution

It provides new evidence that void environments significantly enhance AGN activity and black hole accretion, using combined optical spectroscopic and mid-IR analysis across different galaxy regions.

Findings

Higher fraction of AGN and star-forming galaxies in voids

Stronger nuclear activity observed in voids

Large fraction of massive black holes with strong accretion in voids

Abstract

We study the population of active galaxies in void environment in the SDSS. We use optical spectroscopic information to analyze characteristics of the emission lines of galaxies, accomplished by WHAN and BPT diagrams. Also, we study WISE mid-IR colours to assess AGN activity. We investigate these different AGN classification schemes, both optical and mid-IR, and their dependence on the spatial location with respect to the void centres. To this end, we define three regions: void, the spherical region defined by voidcentric distance relative to void radius (distance/r$_{\rm void}$) smaller than 0.8, comprising overdensities lesser than -0.9, an intermediate/transition shell region (namely void--wall) 0.8 $<$ distance/r$_{\rm void} <$ 1.2, and a region sufficiently distant from voids, the field: distance/r$_{\rm void} >$ 2. We find statistical evidence for a larger fraction of AGN and star--forming galaxies in the void region, regardless of the classification scheme addressed (either BPT, WHAN or WISE). Moreover, we obtain a significantly stronger nuclear activity in voids compared to the field. We find an unusually large fraction of the most massive black holes undergoing strong accretion when their host galaxies reside in voids. Our results suggest a strong influence of the void environment on AGN mechanisms associated with galaxy evolution.