Simulating the formation of disk galaxies: The impact of Jets from Active Galactic Nuclei

Recent semi-analytic models have highlighted the role of AGN jets in regulating the formation of galaxies. In this paper, we present a new implementation of feedback due to active galactic nuclei (AGN) in cosmological hydrodynamic simulations of galaxy formation in which AGN feedback is assumed to heat the halo gas through the production of jets. Combining a theoretical model of mass accretion onto black holes with a multiphase description of star-forming gas, we self-consistently follow evolution of both galaxies and their central black holes. The novelty in our model is that we consider the two distinct accretion modes: standard radiatively efficient thin accretion disks and radiatively inefficient accretion flows which we will generically refer to as RIAFs; motivated by the theoretical models for jet production in accretion disks, we assume that only the RIAF is responsible for the production of powerful jets. The focus of this paper is to investigate the interplay between galaxies and their central black holes during the formation of a disc galaxy. We find that, after an initial episode of bursting star formation, the accretion rate of the central black hole drops so that the accretion disk switches to a RIAF structure. At this point, the feedback from the AGN becomes highly efficient and strongly suppresses further star formation in the galaxy’s bulge. Disk star formation continues, however, and the galaxy becomes a disc-dominated galaxy with B-band disc-tototal luminosity ratio, D/T ≃ 0.8, and old central stellar population of V -band luminosity weighted age ∼ 9.5 Gyr. Thus, while AGN jet feedback does not prohibit the disc formation, it is responsible for formation of old, red bulges in disc galaxies.