A Full Active Galactic Nuclei Feedback Prescription for Numerical Models: Negative, Positive, and Hot Gas-ejection Modes

Abstract

We build upon the state-of-the-art semianalytic model FEGA24 for the formation and evolution of galaxies, which integrates the latest prescriptions relevant to galaxy formation and evolution, alongside a comprehensive active galactic nuclei (AGN) feedback model. This model incorporates three modes of feedback: negative (preventing excessive cooling), positive (enhancing star formation), and hot gas ejection (expelling gas beyond the virial radius of halos). These modes operate in a coordinated manner: the negative mode regulates the cooling process, the positive mode promotes bursts of star formation, and the hot gas ejection mode expels gas beyond the virial radius when the AGN is sufficiently powerful. Our updated semianalytic model, FEGA25 , retains the qualitative and quantitative consistency of the analyses presented by E. Contini et al. (2024a), while delivering more robust results. Notably, FEGA25 provides a more detailed characterization of the fraction of passive galaxies as a function of stellar mass and redshift, and predicts a main sequence of star-forming galaxies more consistent with observations and a more accurate cosmic star formation rate density with redshift. Moreover, it estimates the fraction of hot gas in halos closer to observed values. These findings underscore the importance of a physical mechanism capable of ejecting hot gas beyond the virialized region of dark matter halos without significantly altering the stellar and cold gas components. Such a mechanism is crucial to ensure the proper functioning of other processes, such as cooling and star formation. Since supernova feedback is already modeled at its maximum efficiency, AGN feedback emerges as the natural candidate for this role.

Keywords

• Galaxy formation
• Galaxy evolution