Speaker
Description
We present new two-fluid models of accretion disks in active galactic nuclei (AGN) that aim to resolve the long-standing problem of Toomre instability in AGN outskirts. In the spirit of earlier work by Sirko Goodman 2003 and others, we argue that Toomre instability is eventually resolved via feedback produced by fragmentation and its aftermath. Unlike past semi-analytic models, which (i) adopt local prescriptions to connect star formation rates to heat feedback, and (ii) assume that AGN disks self-regulate by star-forming, we find that feedback processes are both temporally and spatially non-local. The accumulation of many stellar-mass black holes (BHs) embedded in AGN gas eventually displaces stellar winds and supernovae as the dominant feedback source. The non-locality 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 a Toomre parameter much greater than 1 and no ongoing star formation. We explore the implications of our two-fluid disk models for the evolution of compact object populations embedded in AGN disks, and find self-consistent solution in much of the parameter space of AGN mass and accretion rate. These solutions harbor large populations of embedded compact objects which 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 are significantly different in structure from commonly used 1D disk models, which has broad implications for gravitational wave source formation inside AGN.
