Black holes in the low-mass galaxy regime

Context. Active galactic nuclei (AGNs) have been observed in dwarf galaxies, yet the impact of black hole feedback in these low-mass systems remains unclear. Aims. To uncover the potential effects of AGNs in the low-mass galaxy regime, we study the properties and demographics of active dwarf galaxies at z = 0, using IllustrisTNG simulations. Methods. We used data from the TNG50-1 simulation, selecting central galaxies with stellar masses in the range 8 ≤ log(M*/M⊙)≤9.5, along with a selection of AGNs based on their Eddington ratios (λEdd). We analyzed the properties and environment of AGN host galaxies and compared them with inactive control galaxies. Results. The AGN fractions found in the simulation depend strongly on the threshold for λEdd in the AGN selection, ranging from ∼1% (λEdd ≥ 0.05) to ∼24% (λEdd ≥ 0.01). In comparison with non-AGN galaxies of similar stellar and halo mass, dwarf AGN hosts are deficient in neutral gas, having ∼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 ≳ 3 kpc), and AGN hosts have more extended gas components than non-AGN galaxies, with a gas half-mass radius that is ≳10 kpc larger, on average. AGN hosts also display slightly less star-forming activity, but there are no differences seen in terms of the local environment. Conclusions. We found that AGNs can significantly decrease the neutral gas component of dwarf galaxies, which is 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 AGNs 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.