The AGN Feedback in Compact Galaxies: On the Impact of a More Massive Central Black Hole

Abstract

Abstract We conduct high-resolution hydrodynamical simulations using the MACER framework to investigate the interplay between the interstellar medium, active galactic nuclei (AGN) feedback and black hole (BH) feeding in a massive compact galaxy, with an emphasis on the impact of different central BH masses. We find that with a more massive central BH, high-speed outflows are more prominent, and the gas fraction in the compact galaxy is reduced. Due to the lower gas density and higher gas temperature, the compact galaxy with a more massive BH (MAS galaxy) remains predominantly single-phase with the cooling time t cool ≳ 100t ff. In contrast, the compact galaxy with the reference BH mass (REF galaxy) maintains a higher gas fraction with a shorter cooling time, slightly more multiphase gas and less prominent outflows. We further demonstrate that the difference in gas thermal states and kinematics is caused by the stronger AGN feedback in the compact galaxy with a more massive BH, where the AGN wind power is twice as much as that with the reference BH. Since the AGN feedback efficiently suppresses the inflow rate and the BH feeding rate, the BH mass growth is significant in neither the compact galaxy with the reference BH nor that with the more massive BH, only by 24% and 11% of the initial BH mass, respectively, over the entire evolution time of 10 Gyr. We thus posit that without ex situ mass supply from mergers, the massive BHs in compact galaxies cannot grow significantly via gas accretion during the late phase, but might have already formed by the end of the rapid early phase of galaxy formation.