AGN have Underweight Black Holes and Reach Eddington

TL;DR

This paper proposes that supermassive black holes in AGN are generally underweight relative to the $M - \sigma$ relation due to Rayleigh--Taylor instabilities, and that they spend most of their lives accreting at the Eddington rate, explaining observed outflows.

Contribution

It introduces a new explanation for black hole mass regulation in AGN based on Rayleigh--Taylor instability effects on outflows, aligning with recent observations of ultrafast X-ray outflows.

Findings

SMBH masses are likely below the $M - \sigma$ relation due to instabilities.

AGN black holes predominantly accrete at the Eddington rate.

Widespread ultrafast X-ray outflows support the high accretion rate hypothesis.

Abstract

Eddington outflows probably regulate the growth of supermassive black holes (SMBH) in AGN. I show that effect of the Rayleigh--Taylor instability on these outflows means that SMBH masses are likely to be a factor of a few below the $M - \sigma$ relation in AGN. This agrees with the suggestion by Batcheldor (2010) that the $M - \sigma$ relation defines an upper limit to the black hole mass. I further argue that observed AGN black holes must spend much of their lives accreting at the Eddington rate. This is already suggested by the low observed AGN fraction amongst all galaxies despite the need to grow to the masses required by the Soltan relation, and is reinforced by the suggested low SMBH masses. Most importantly, this is the simplest explanation of the recent discovery by Tombesi et al (2010a, b) of the widespread incidence of massive ultrafast X--ray outflows in a large sample of AGN.