Bulge Formation at Intermediate Redshift
Lauren MacArthur
June 20-22, 2007
We are addressing these and other related questions with a sample of bulges
spanning the redshift range 0.1<z<1.0 selected from the GOODS survey.
We use the GOODS HST-ACS imaging (left panels) to extract the photometric
parameters of the bulge component using simultaneous bulge-to-disk
decompositions (middle panels) and spectroscopy from DEIMOS
on Keck to derive kinematic parameters (right panels; upper is the velocity
dispersion profile, lower is the rotation curve). These data allow us to
construct the Fundamental Plane for our distant bulges which, in turn,
yields constraints their mass assembly history. Our analysis
culminates with a comparison of our results with similar analyses of pure
spheroidal galaxies (ellipticals and lenticulars) and with predictions from
hierarchical galaxy formation models to help distinguish between the above
scenarios for bulge formation and evolution.
The history of the formation and evolution of galactic bulges remains a key
issue in understanding the origin of the Hubble sequence.
Originally thought to form at high redshift as "miniature ellipticals"
through dissipationless collapse, their continued growth as predicted via
the merging of smaller fragments in hierarchical
models is consistent with the diversity observed in their present-day stellar
populations. However, what governs this growth and whether it is related to
the properties of galactic disks is unclear. Some authors have argued for
a secular bulge growth by the dynamical rearrangement of disk material in
the presence of a bar, while others argue that bulges follow the same
evolutionary path as pure spheroidal galaxies. Any bulge evolution scenario
must also be consistent with the tight empirical correlation between
bulge and central black hole masses. The wide range in physical scales
spanned by these scaling relations presents a major theoretical challenge.