Departmental Colloquium

Radiation Pressure, Starburst Disks, and the Fueling of Active Galactic Nuclei

Prof. Norman Murray, Director of CITA
University of Toronto

Time
Wed. November 28, 2007     3:30 PM     Stirling A

Abstract

Radiation pressure is dynamically important in the inner regions of starburst galaxies and ultraluminous infrared galaxies (ULIRGs), a point made by Nick Scoville. This insight leads to a simple Eddington-like argument which shows that a galaxy with a velocity dispersion $\sigma$ has a maximum luminosity $L\approx 4f_g\sigma^4 c/G$, where $f_g$ is the fraction of the galaxie's mass in the form of gas. The luminosity might come either from stars or a central black hole. This strongly suggests that radiation pressure is involved in both the Faber-Jackson relation (linking the luminosity of an elliptical galaxy to its velocity dispersion) and the M-$\sigma$ relation between the velocity dispersion of ellipticals or bulges and the mass of the central black hole. I will argue that radiation pressure is also the key missing ingredient in models of black hole feeding on scales of a few tenths to a few tens of parsecs. The radiation is supplied by star formation in marginally Toomre-stable disks; the support is via radiation pressure on dust, allowing the disk to maintain Q=1 at small radii without exorbitant amounts of mass consumption. Simple disk models can explain many of the features of starbursts, ULIRGs, Seyferts, and quasars. I will describe some observational tests of these disk models on scales of 0.1-1 parsec in nearby Seyfert II galaxies, using water masers. Adaptive optics in the near infrared offer the possibility of testing the models on somewhat larger scales.

Refreshments available from 3:15

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