Bulge Building with Mergers and Winds

Abstract

The gravitational clustering hierarchy and dissipative gas processes are both involved in the formation of bulges. Here we present a simple empirical model in which bulge material is assembled via gravitational accretion of the visible companion galaxies. Assuming that merging leads to a starburst, we show that the resulting winds can be strong enough that they self-regulate the accretion. A quasi-equilibrium accretion process naturally leads to the Kormendy relation between bulge density and size. Whether or not the winds are sufficiently strong and long lived to create the quasi-equilibrium must be tested with observations. To illustrate the model we use it to predict representative parameter dependent star formation histories. We find that bulge building activity peaks around redshift two, with tails to both higher and lower redshifts.