A look at three different scenarios for bulge formation

In this paper we present three qualitatively different scenarios for bulge formation: a secular evolution model in which bulges form after disks and undergo several central starbursts, a primordial collapse model in which bulges and disks form simultaneously, and an early bulge formation model in which bulges form prior to disks. We normalize our models to the local z = 0 observations of de Jong & van der Kruit and Peletier & Balcells and make comparisons with high-redshift observations. We consider model predictions relating directly to bulge-to-disk properties. As expected, smaller bulge-to-disk ratios and bluer bulge colors are predicted by the secular evolution model at an redshifts, although uncertainties in the data are currently too large to differentiate strongly between the models.