Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

The Active Galactic Nuclei In Cosmological Simulations (AGNICS) project includes AGN into the GalICS hybrid (N-body + semi-analytic) model to explore the quasar-galaxy link in a cosmological perspective. The key problems are the quasar fuelling mechanism, the origin of the BH to bulge mass relation, the causal and chronological link between BH growth and galaxy formation, the properties of quasar hosts and the role of AGN feedback in galaxy formation. This first paper has two goals: to describe the general structure and the assumptions of the method, and to apply AGNICS to studying the joint formation of BHs and spheroids in galaxy mergers. We investigate under what conditions this scenario can reproduce the local BH distribution and the evolution of the quasar population. AGNICS contains two star formation modes: a quiescent one in discs and a starburst one in protospheroids, the latter triggered by mergers and disc instabilities. We assume that BH growth is linked to the starburst mode. The simplest version of this scenario, in which the BH accretion rate and the star formation rate in the starburst component are simply related by a constant of proportionality, does not to reproduce the cosmic evolution of the quasar population. A model in which this relation is modulated by a scaling with the square root of the starburst gas density can explain the evolution of the quasar luminosity function in B-band and X-rays (accounting for the obscuration inferred from X-ray studies). The scatter and the tilt that this model introduces in the BH-to-bulge mass relation are within the observational constraints. The quasar contribution grows with bolometric luminosity and for a given bulge mass the most massive BHs are in the bulges with the oldest stars.

Abstract:

The very high rates of second generation star formation detected and inferred in high redshift objects should be accompanied by intense millimetre-wave emission from hot core molecules. We calculate the molecular abundances likely to arise in hot cores associated with massive star formation at high redshift, using several independent models of metallicity in the early Universe. If the number of hot cores exceeds that in the Milky Way Galaxy by a factor of at least one thousand, then a wide range of molecules in high redshift hot cores should have detectable emission. It should be possible to distinguish between independent models for the production of metals and hence hot core molecules should be useful probes of star formation at high redshift.