Pseudobulge Formation as a Dynamical Rather than a Secular Process
  We investigate the formation and evolution of the pseudobulge in "Eris", a
high-resolution N-body + smoothed particle hydrodynamics (SPH) cosmological
simulation that successfully reproduces a Milky Way-like massive late-type
spiral in a cold dark matter (LCDM) universe. At the present epoch, Eris has a
virial mass Mvir=8x10^11 Msun, a photometric stellar mass M*=3.2x10^10 Msun, a
bulge-to-total ratio B/T = 0.26, and a weak nuclear bar. We find that the bulk
of the pseudobulge forms quickly at high redshift via a combination of
non-axisymmetric disk instabilities and tidal interactions or mergers both
occurring on dynamical timescales, not through slow secular processes at lower
redshift. Its subsequent evolution is not strictly secular either, and is
closely intertwined with the evolution of the stellar bar. In fact, the
structure that we recognize as a pseudobulge today evolves from a stellar bar
that formed at high redshift, was destroyed by minor mergers at z~3, reformed
shortly after, and weakened again following a steady gas inflow at z<1. The
gradual dissolution of the bar ensues at z=1 and continues until the present
without increasing the stellar velocity dispersion in the inner regions. In
this scenario the pseudobulge is not a separate component from the inner disk
in terms of formation path, rather it is the first step in the inside-out
formation of the baryonic disk, in agreement with the fact that pseudobulges of
massive spiral galaxies have typically a dominant old stellar population. If
our simulations do indeed reproduce the formation mechanisms of massive
spirals, then the progenitors of late-type galaxies should have strong bars and
small photometric pseudobulges at high redshift.
