Uncovering Drivers of Disk Assembly: Bulgeless Galaxies and the Stellar
  Mass Tully-Fisher Relation
  In order to determine what processes govern the assembly history of galaxies
with rotating disks, we examine the stellar mass Tully-Fisher relation over a
wide range in redshift partitioned according to whether or not galaxies contain
a prominent bulge. Using our earlier Keck spectroscopic sample, for which
bulge/total parameters are available from analyses of HST images, we find that
bulgeless disk galaxies with z > 0.8 present a significant offset from the
local Tully-Fisher relation whereas, at all redshifts probed, those with
significant bulges fall along the local relation. Our results support the
suggestion that bulge growth may somehow expedite the maturing of disk galaxies
onto the Tully-Fisher relation. We discuss a variety of physical hypotheses
that may explain this result in the context of kinematic observations of
star-forming galaxies at redshifts z = 0 and z > 2.
