UC Berkeley

This thesis explores two topics in contemporary galaxy evolution using numerical models and N-body simulation: feedback in active galactic nuclei and the heating of stellar disks.

Two numerical models of feedback from active galactic nuclei are developed and applied to the case of a major merger between two disk galaxies. Accretion into central black holes is modeled via a subgrid prescription based on angular momentum transport on unresolved scales. Feedback from black holes is modeled in two ways, both of which deposit a momentum &tau L / c into the surroundings, where L is the luminosity of radiation produced by the galactic nucleus. In the first model, the momentum is divided equally among the nearby gas particles to model processes like the absorption of ultraviolet light by dust grains. The second model deposits the same amount of momentum into the surroundings, but it does so by launching a wind with a fixed speed, which only has a direct effect on a small fraction of the gas in the black hole's vicinity. Both models successfully regulate the growth of the black hole, reproducing, for example, the M_BH-&sigma relationship, albeit for large amounts of momentum deposition (large &tau). This regulation is largely independent of the fueling model employed, and thus is `demand limited' black hole growth, rather than a `supply limited' mode. However, only the model that implements an active galactic nucleus wind explicitly has an effect on large scales, quenching star formation in the host galaxy, and driving a massive galaxy-scale outflow.

In a separate set of calculations, a method for including a stellar disk in cosmological zoom-in simulation is presented and applied to a set of realistic dark matter halos taken from the Aquarius suite of simulations. The halos are adiabatically adjusted from z = 1.3 to z = 1.0 by a rigid disk potential, at which point the rigid potential is replaced with a live stellar disk of particles. The halos respond to the disks, in every orientation simulated, by contracting in their central regions and by becoming oblate instead of prolate. The resulting disks, with few exceptions, form large bars which contain a fair fraction of the mass of the disk. These bars buckle and dominate the dynamics of the disk, increasing not only the scale height of the disk, but also the vertical velocity dispersion. During the simulations, the disks tumble coherently with their host halo, but can leave the outermost edges of the disk behind, creating streams that are far out of the plane of the disk. Some first steps are taken to relate the evolution of the disk to the substructure in the halo, but the situation is complicated by the massive bar.