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

We introduce the state-of-the-art semi-analytic model FEGA (Formation and Evolution of GAlaxies), which incorporates updated prescriptions for key physical processes in galaxy formation. Notably, 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. FEGA is rigorously calibrated using an MCMC procedure to match the evolution of the stellar mass and K-band luminosity functions from high redshift to the present, and the local black hole-bulge mass relation. 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 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.