Black holes in the low-mass galaxy regime: imprint of AGN feedback on the circumgalactic medium of central dwarf galaxies

TL;DR

This study uses the IllustrisTNG simulations to explore how active galactic nuclei influence the gas content and properties of low-mass dwarf galaxies, revealing significant gas depletion linked to AGN activity.

Contribution

It demonstrates that AGN feedback can substantially reduce neutral gas in dwarf galaxies within cosmological simulations, a novel insight into low-mass galaxy evolution.

Findings

AGN hosts have 3.9 times less neutral gas than inactive dwarfs.

AGN hosts exhibit more extended gas components, with half-mass radii over 10 kpc larger.

Dwarf AGN fractions in simulations are much higher than observed, indicating a need for further investigation.

Abstract

Active galactic nuclei (AGN) have been observed in dwarf galaxies, yet the impact of black hole feedback in these low-mass systems remains unclear. To uncover the potential effects of AGN in the low-mass galaxy regime, we study the properties and demographics of active dwarf galaxies at $z=0$, using the IllustrisTNG simulations. We use data from the TNG50-1 simulation, selecting central galaxies with stellar masses in the range $8 \leq \log(M_\ast/{\rm M_\odot}) \leq 9.5$, and selecting AGN based on their Eddington ratio ($\lambda_{\rm Edd}$). We analyzed the properties and environment of AGN host galaxies and compared them with inactive control galaxies. The AGN fractions found in the simulation depend strongly on the threshold for $\lambda_{\rm Edd}$ in the AGN selection, ranging from $\sim$ 1\% ($\lambda_{\rm Edd} \geq 0.05$) to $\sim$ 24\% ($\lambda_{\rm Edd} \geq 0.01$). In comparison with non-AGN galaxies of similar stellar and halo mass, dwarf AGN hosts are deficient in neutral gas, having $\sim$ 3.9 times less neutral mass, in qualitative agreement with observations. The dearth in neutral gas is stronger beyond two stellar half-mass radii ($r \gtrsim 3$ kpc), and AGN hosts have more extended gas components than non-AGN galaxies, with a gas half-mass radius, on average, $\gtrsim$ 10 kpc larger. AGN hosts are also slightly less star-forming, but have no differences in local environment. We found that AGN can significantly decrease the neutral gas component of dwarf galaxies, a direct effect of the high-accretion feedback mode employed in IllustrisTNG. However, it is important to test our findings with observations to unveil the complete role of AGN in dwarf galaxies. In TNG50, dwarf AGN fractions are an order of magnitude larger than those observed, motivating a detailed investigation to precisely quantify the mismatch between simulations and observations.