Physical Society Colloquium

A Statistical Model Of Black-Hole Growth And Star Formation in Galaxies

George Helou

Caltech

Accretion onto black holes and star formation are closely related evolutionary agents for galaxies over cosmic time. The physics of this evolution are so rich that direct numerical modeling is still far from generating a realistic representation to be confronted with data. Statistical descriptions of galaxy populations can expose evolutionary trends relating the two energy sources, and point to the physical underpinnings of evolutionary trends.

We present the first synthetic model describing a galaxy in terms of both accretion and star formation, and building up to populations of galaxies using well observed luminosity functions and spectral energy distributions in the Local Universe. X-ray data relate primarily to the black hole accretion component, whereas infrared data constrain star formation rates and the balance between accretion and star formation power. The model parameters are set by fitting to a variety of data from sky surveys, then model predictions are tested against trends derived from other data sets. The model's cosmic evolution scenario can then be used to assess the importance of various physical processes to the evolution of galaxies at various epochs.