Times, environments and channels of bulge formation in a LambdaCDM
  cosmology
  We analyze predictions from two independently developed galaxy formation
models to study the mechanisms, environments, and characteristic times of bulge
formation in a LambdaCDM cosmogony. For each model, we test different
prescriptions for bulge formation in order to quantify the relative importance
of different channels. Our results show that the strong correlation between
galaxy and halo mass for central galaxies, and the richer merger history of
more massive systems naturally give rise to a strong correlation between galaxy
mass and morphology, and between halo mass and morphological type of central
galaxies. Large fractions of the bulge mass are acquired through major and
minor mergers, but disc instability plays an important role, particularly for
intermediate mass galaxies. We find that the modelling of disc instability
events, as well as of the galaxy merger times, can affect significantly the
timing of bulge formation, and the relative importance of different channels.
Bulge dominated galaxies acquire their morphology through major mergers, but
this can be modified by cooling of gas from the surrounding hot halo. We find
that disc regrowth is a non negligible component of the evolution of bulge
dominated galaxies, particularly for low to intermediate masses, and at high
redshifts.
