The Galaxy–Active Galactic Nucleus Scaling Relations over 13 Billion Years in <scp>SHARK</scp> v2.0. I. Supermassive Black Hole Masses

Abstract The presence of strong correlations between supermassive black hole (SMBH) masses and galaxy properties like stellar mass have been well established for the local Universe, but how these scaling relations evolve with cosmic time is yet to be settled in both observations and theoretical models. Recent works have also highlighted the role of galaxy morphology on the scatter of the SMBH–galaxy mass scaling relations, while the impact of other galaxy properties remains poorly studied, like the role of galaxy environment. We use the state-of-the-art shark v2.0 semianalytic model to explore the evolution of these galaxy–SMBH scaling relations to expand the available predictions from theoretical models to contrast with existing and upcoming observations. We find the relations between SMBH masses and both total and bulge stellar masses predicted by shark v2.0 to be in good overall agreement with observational measurements across a wide range of redshifts and stellar masses. These scaling relations show a significant evolution as a function of cosmic time in shark v2.0, with SMBH masses ∼1 dex lower at z = 0 compared to z = 9 at fixed stellar mass and the scatter increasing by a factor of ∼2–5 toward low redshift. Both relations show a strong dependence with galaxy morphology and the main source for SMBH growth (gas accretion or mergers), with weaker trends with star formation rate, galaxy size, and environment. We find that galaxy morphology alone explains most of the scatter around both scaling relations, with other galaxy properties tying to the SMBH scaling relations through their correlations with morphology.