The Impact of Positive AGN Feedback on the Properties of Galaxies in a Semi-Analytic Model of Galaxy Formation

TL;DR

This paper presents FEGA, a sophisticated semi-analytic galaxy formation model that uniquely incorporates positive AGN feedback, improving the match to observed galaxy scaling relations without disrupting existing physical prescriptions.

Contribution

The novel aspect is the implementation of a positive AGN feedback mode in a semi-analytic model, calibrated to observed galaxy properties, enhancing the understanding of galaxy evolution.

Findings

Positive AGN feedback coexists with negative feedback in the model.

Inclusion of positive feedback improves agreement with observed galaxy scaling relations.

Model successfully reproduces various galaxy properties across redshifts.

Abstract

We introduce the state-of-the-art semi-analytic model {\small FEGA} (Formation and Evolution of GAlaxies), which incorporates updated prescriptions for key physical processes in galaxy formation. Notably, {\small FEGA} features an unprecedented semi-analytic modeling of positive Active Galactic Nuclei (AGN) feedback. The model combines the latest prescriptions for gas infall and cooling, a revised star formation recipe that incorporates the extended Kennicutt-Schmidt relation, disk instability, updated supernovae feedback, reincorporation of ejected gas, hot gas stripping from satellite galaxies, and the formation of diffuse light. A novel description of AGN feedback is introduced, describing the positive mode as a burst of star formation from a cooling gas fraction. {\small FEGA} is rigorously calibrated using an MCMC procedure to match the evolution of the stellar mass function from high redshift to the present. Subsequently, the model is tested against several observed and predicted scaling relations, including the star formation rate-mass, black hole-bulge and stellar mass, stellar-to-halo mass, and red fraction-mass relations. Additionally, we test {\small FEGA} against other galaxy properties such as the distribution of specific star formation rates, stellar metallicity and morphology. Our results demonstrate that the inclusion of positive AGN feedback can co-exist with its negative counterpart without drastic alterations to other prescriptions. Importantly, this inclusion improves the ability of the model to describe the primary scaling relations observed in galaxies.