The impact of cosmic voids on AGN activity

¹ Instituto de Astrofísica, Pontificia Universidad Católica de Chile Av. Vicuña Mackenna 4860 Santiago, Chile
² Centro de Astro-Ingeniería, Pontificia Universidad Católica de Chile Santiago, Chile
³ Donostia International Physics Centre (DIPC) Paseo Manuel de Lardizabal 4 20018 Donostia-San Sebastian, Spain
⁴ Departamento de Física, Universidad de Córdoba, Campus Universitario de Rabanales Ctra. N-IV Km. 396 E-14071 Córdoba, Spain
⁵ International Centre for Radio Astronomy Research, The University of Western Australia 35 Stirling Highway Crawley WA 6009, Australia

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 17 April 2025
Accepted: 16 December 2025

Abstract

Aims. Our goal is to carry out a comparative study of the properties of central galaxies hosting active galactic nuclei (AGN) in cosmic voids and their surrounding structures (i.e. filaments and walls) at z = 0, comparing them to non-AGN galaxies in similar environments.

Methods. We used the central galaxies selected from the EAGLE project, combined with a void catalogue that identifies voids, filaments, and walls. We categorised our sample of central galaxies into four global environments based on their distance to the nearest void. We analysed several properties such as the star formation activity and black hole mass, as a function of stellar mass and environment for galaxies with and without AGN.

Results. We found that the AGN fraction decreases as a function of void-centric distance, with void galaxies displaying the highest AGN fraction (12%), while galaxies in denser environments, display the lowest AGN fraction (6.7%), consistent with observations. The AGN fraction is particularly high in most massive void galaxies when controlling for stellar mass. When comparing AGN host galaxies to inactive ones, we find that AGN galaxies tend to have slightly more massive supermassive black holes (SMBHs), higher specific star formation rates (sSFRs), and a tendency to reside in higher mass haloes at a given stellar mass than non-AGN galaxies. At M_∗ > 10^10.2 M_⊙, AGN hosts in voids tend to have slightly more massive SMBHs than those in denser environments. Otherwise, the AGN population does not show a clear trend in relation to the global environment. In contrast, non-AGN void galaxies host more massive SMBHs, slightly higher sSFRs, and are located in more massive haloes than those in denser environments. Analysing the recent merger histories of both AGN and non-AGN populations, we find that a larger fraction of massive AGN galaxies have undergone major mergers compared to non-AGN galaxies, regardless of environment. Notably, AGN galaxies in voids show a higher frequency of recent mergers (especially major mergers) than their counterparts in other environments, particularly at high stellar mass.

Conclusions. Our results suggest that the evolution of SMBHs in voids is closely related to that of their host galaxies and their surrounding environment, while the most recent AGN activity is more strongly linked to recent interactions.