Feedback-Dominated Accretion Flows
  We present new two-fluid models of accretion disks in active galactic nuclei
(AGNs) that aim to address the long-standing problem of Toomre instability in
AGN outskirts. In the spirit of earlier works by Sirko & Goodman and others, we
argue that Toomre instability is eventually self-regulated via feedback
produced by fragmentation and its aftermath. Unlike past semianalytic models,
which (i) adopt local prescriptions to connect star formation rates to heat
feedback, and (ii) assume that AGN disks self-regulate to a star-forming steady
state (with Toomre parameter Q=1), we find that feedback processes are both
temporally and spatially nonlocal. The accumulation of many stellar-mass black
holes (BHs) embedded in AGN gas eventually displaces radiation, winds and
supernovae from massive stars as the dominant feedback source. The nonlocality
of feedback heating, in combination with the need for heat to efficiently mix
throughout the gas, gives rise to steady-state AGN solutions that can have Q>>1
and no ongoing star formation. We find self-consistent steady-state solutions
in much of the parameter space of AGN mass and accretion rate. These solutions
harbor large populations of embedded compact objects that may grow in mass by
factors of a few over the AGN lifetime, including into the lower and upper mass
gaps. These feedback-dominated AGN disks differ significantly in structure from
commonly used 1D disk models, which has broad implications for
gravitational-wave-source formation inside AGNs.
