Formation of Galactic Bulges

We use cosmological hydrodynamic simulations to investigate the formation of galactic bulges within the framework of hierarchical clustering in a representative cold dark matter (CDM) cosmological model. We show that the largest objects forming at cosmological redshifts z ~ 4 resemble observed bulges of spiral galaxies or moderate-sized ellipticals in their general properties, such as size, shape, and density profile. This is consistent with observational data indicating the existence of "old" bulges and ellipticals at more moderate redshifts. These bulges are gas dominated at redshift z = 3, with high rates of star formation, and would appear to be good candidates for small blue galaxies seen in the Hubble Deep Field.