Thermal and radiative AGN feedback : weak impact on star formation in high-redshift disk galaxy simulations

TL;DR

This study uses high-resolution simulations of a high-redshift galaxy with an active nucleus to show that AGN feedback has a minimal immediate effect on star formation, despite powerful outflows.

Contribution

It demonstrates that AGN heating and radiative feedback have a weak impact on star formation rates in high-redshift disk galaxies, even with long-range radiation effects included.

Findings

AGN outflows remove gas but do not significantly suppress star formation.

Star formation rate decreases by only a few percent under quasar-like conditions.

Atomic gas reservoirs are marginally affected by AGN feedback.

Abstract

Active Galactic Nuclei (AGNs) release huge amounts of energy in their host galaxies, which, if the coupling is sufficient, can affect the interstellar medium (ISM). We use a high-resolution simulation ($\sim6$ pc) of a z $\sim2$ star-forming galaxy hosting an AGN, to study this not yet well-understood coupling. In addition to the often considered small-scale thermal energy deposition by the AGN, which is implemented in the simulation, we model long-range photo-ionizing AGN radiation in post-processing, and quantify the impact of AGN feedback on the ability of the gas to form stars. Surprisingly, even though the AGN generates powerful outflows, the impact of AGN heating and photo-ionization on instantaneous star formation is weak: the star formation rate decreases by a few percent at most, even in a quasar regime ($L_{bol}=10^{46.5}$ erg s$^{-1}$). Furthermore, the reservoirs of atomic gas that are expected to form stars on a 100 - 200 Myrs time scale are also marginally affected. Therefore, while the AGN-driven outflows can remove substantial amounts of gas in the long term, the impact of AGN feedback on the star formation efficiency in the ISM of high-redshift galaxies is marginal, even when long-range radiative effects are taken into account.