The impact of cosmic voids on AGN activity

TL;DR

The study investigates how cosmic voids and surrounding large-scale structures influence AGN triggering and SMBH–host co-evolution using the EAGLE cosmological hydrodynamical simulation. By pairing central galaxies with a void catalogue and classifying environments via void-centric distance, the authors compare AGN and non-AGN populations at $z=0$ and trace their evolution to earlier times. They find that AGN fractions are highest in void interiors and lowest in skeleton regions, with AGN host galaxies tending to have more massive SMBHs and reside in somewhat more massive haloes; non-AGN void galaxies can also host substantial BHs and halo masses. The results point to mergers, especially major mergers, as a primary driver of recent AGN activity, with void environments showing a pronounced merger–AGN connection at high stellar masses, highlighting the nuanced role of large-scale environment in SMBH growth and galaxy evolution.

Abstract

From the Eagle project, we study the properties of galaxies hosting AGN in cosmic voids and their surrounding structures, filaments and walls, at $z=0$, comparing them to non-AGN galaxies in similar environments. We found that the AGN fraction decreases as a function of void-centric distance, with void galaxies displaying the highest AGN fraction (12\%), and galaxies in denser environments, showing 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 SMBHs, higher specific star formation rates, and reside in higher-mass haloes at a given stellar mass than non-AGN galaxies. At $\rm M_{*} > \rm 10^{10.2} \rm M_{\odot}$, 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, especially at high stellar mass. 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.

Figures (13)

• Figure 1: Stellar mass distribution of the AGN (top panel) and the non-AGN galaxies (bottom panel) in the inner void (blue), outer void (green), skeleton (magenta), and wall (orange) cosmic environments. The vertical lines denote the median stellar mass for each environment. We note that the AGN and non-AGN samples have been drawn from galaxy samples in each environment that have matching stellar mass distributions rosasg2022. Error bars show the 16th and 84th percentiles from the bootstrap distribution of 1000 samples.
• Figure 2: AGN fraction as a function of stellar mass for galaxies in each defined environment. Galaxies in under-dense environments are more likely to host an AGN than those in denser environments, particularly for $\rm M_{*} \sim 10^{10.5} \rm M_{\odot}$, at $z=0$. Errors show the 16th and 84th percentiles from the bootstrap distribution of 1000 samples.
• Figure 3: Top: Log sSFR as a function of stellar mass for AGN (left) and non-AGN (right). The circle points are the median value of the log sSFR in that stellar mass range. The error bars denote the bootstrap errors in each stellar mass interval. Each point has been slightly shifted along the x-axis so that the error bars are visible. Bottom left: Ratio between the log sSFR of Out-V, S, W, and all AGN host galaxies to In-V. Bottom right: Ratio between the log sSFR of Out-V, S, W, and all non-AGN host galaxies to In-V (see Section \ref{['subsec:voidsineagle']} for definitions).
• Figure 4: Same as Fig. \ref{['fig:comp_SFR_boot']} for log $M_{\rm BH}$ as a function of stellar mass.
• Figure 5: Same as Fig. \ref{['fig:comp_SFR_boot']} for the log($M_{\rm *}$)-log($M_{\rm halo}$) relation.