Do we expect most AGN to live in discs?
Abstract
Recent observations have indicated that a large fraction of the low- to intermediate-luminosity AGN population lives in disc-dominated hosts, while the more luminous quasars live in bulge-dominated hosts (that may or may not be major merger remnants), in conflict with some previous model predictions. We therefore build and compare a semi-empirical model for AGN fuelling which accounts for both merger and non-merger 'triggering'. In particular, we show that the 'stochastic accretion' model – in which fuelling in disc galaxies is essentially a random process arising whenever dense gas clouds reach the nucleus – provides a good match to the present observations at low/intermediate luminosities. However, it falls short of the high-luminosity population. We combine this with models for major merger-induced AGN fueling, which lead to rarer but more luminous events, and predict the resulting abundance of disc-dominated and bulge-dominated AGN host galaxies as a function of luminosity and redshift. We compile and compare observational constraints from z ∼ 0 to 2. The models and observations generically show a transition from disc to bulge dominance in hosts near the Seyfert-quasar transition, at all redshifts. 'Stochastic' fuelling dominates AGN by number (dominant at low luminosity), and dominates black hole (BH) growth below the 'knee' in the present-day BH mass function ( ≲ 10^7 M_⊙). However, it accounts for just ∼10 per cent of BH mass growth at masses ≳ 10^8 M_⊙. In total, fuelling in discy hosts accounts for ∼30 per cent of the total AGN luminosity density/BH mass density. The combined model also accurately predicts the AGN luminosity function and clustering/bias as a function of luminosity and redshift; however, we argue that these are not sensitive probes of BH fuelling mechanisms.
Additional Information
© 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 August 22. Received 2014 August 21; in original form 2013 September 15. Support for PFH was provided by NASA through Einstein Postdoctoral Fellowship Award Number PF1-120083 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060. KB was supported by the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan.Attached Files
Published - MNRAS-2014-Hopkins-823-34.pdf
Submitted - 1309.6321v1.pdf
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Additional details
- Eprint ID
- 52212
- Resolver ID
- CaltechAUTHORS:20141201-101549262
- PF1-120083
- NASA Einstein Fellowship
- Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- Created
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2014-12-01Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field