Joint Astrophysics Colloquium

Joint Astrophysics Seminar

On the Maximum Luminosity of Galaxies and Massive Black Holes

Norm Murray

CITA

Radiation pressure is dynamically important in the inner regions of starburst galaxies and ultraluminous infrared galaxies (ULIRGs). This insight leads to a simple Eddington-like argument which shows that a galaxy with a velocity dispersion σ (a measure of the galactic mass) has a maximum luminosity L ~ 4f_gσ⁴ c/G, where f_g is the fraction of the galaxy'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-σ relation between the mass of a galaxy and the mass of that galaxy's 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. 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.