Time-dependent models of AGN disks with radiation from embedded stellar-mass black holes

Abstract: The brightest steady sources of radiation in the universe, active galactic nuclei (AGN), are powered by gas accretion onto a central supermassive black hole (SMBH). The large sizes and accretion rates implicated in AGN accretion disks are expected to lead to gravitational instability and fragmentation, effectively cutting off mass inflow to the SMBH. Radiative feedback from disk-embedded stars has been invoked to yield marginally stable, steady-state solutions in the outer disks. Here, we examine the consequences of this star formation with a semi-analytical model in which stellar-mass black hole (sBH) remnants in the disk provide an additional source of stabilizing radiative feedback. Assuming star formation seeds the embedded sBH population, we model the time-evolving feedback from both stars and the growing population of accreting sBHs. We find that in the outer disk, the luminosity of the sBHs quickly dominates that of their parent stars. However, because sBHs consume less gas than stars to stabilize the disk, the presence of the sBHs enhances the mass flux to the inner disk. As a result, star formation persists over the lifetime of the AGN, damped in the outer disk, but amplified in a narrow ring in the inner disk. Heating from the embedded sBHs significantly modifies the disk's temperature profile and hardens its spectral energy distribution, and direct emission from the sBHs adds a new hard X-ray component.