Momentum Driving: which physical processes dominate AGN feedback?

TL;DR

This paper investigates how different physical processes, especially momentum and mass driving, influence AGN feedback and SMBH growth, revealing that momentum-driven feedback significantly limits black hole mass accumulation.

Contribution

The study demonstrates through simulations that SMBH growth is highly sensitive to momentum and mass feedback, challenging prior models that neglected these effects.

Findings

Omission of momentum feedback causes SMBH mass to be overestimated by a factor of 100.

Including momentum driving results in lower SMBH masses consistent with observations.

Wind efficiencies must be relatively low (less than 10^{-4}) to match observational constraints.

Abstract

The deposition of mechanical feedback from a supermassive black hole (SMBH) in an active galactic nucleus (AGN) into the surrounding galaxy occurs via broad-line winds which must carry mass and radial momentum as well as energy. The effect can be summarized by the dimensionless parameter $\eta=dot{M_outflow}/dot{M_accretion}= (2 \epsilon_w c^2)/v_w^2$ where ($\epslion_w \equiv dot{E}_w/(dot{M_accretion} c^2)$) is the efficiency by which accreted matter is turned into wind energy in the disc surrounding the central SMBH. The outflowing mass and omentum are proportional to $\eta$, and many prior treatments have essentially assumed that $\eta=0$. We perform one- and two-dimensional simulations and find that the growth of the central SMBH is very sensitive to the inclusion of the mass and momentum driving but is insensitive to the assumed mechanical efficiency. For example in representative calculations, the omission of momentum and mass feedback leads to an hundred fold increase in the mass of the SMBH to over $10^{10} \Msun$. When allowance is made for momentum driving, the final SMBH mass is much lower and the wind efficiencies which lead to the most observationally acceptable results are relatively low with $\epsilon_w \lesssim 10^{-4}$.