We investigate possible environmental trends in the evolution of galactic
bulges over the redshift range 0<z<0.6. For this purpose, we construct the
Fundamental Plane (FP) for cluster and field samples at redshifts =0.4 and
=0.54 using surface photometry based on HST imaging and velocity dispersions
based on Keck spectroscopy. As a reference point for our study we include data
for pure ellipticals, which we model as single-component Sersic profiles;
whereas for multi-component galaxies we undertake decompositions using Sersic
and exponential models for the bulge and disk respectively. Although the FP for
both distant cluster and field samples are offset from the local relation,
consistent with evolutionary trends found in earlier studies, we detect
significant differences in the zero point of ~=0.2 dex between the field and
cluster samples at a given redshift. For both clusters, the
environmentally-dependent offset is in the sense expected for an accelerated
evolution of bulges in dense environments. By matching the mass range of our
samples, we confirm that this difference does not arise as a result of the
mass-dependent downsizing effects seen in larger field samples. Our result is
also consistent with the hypothesis that - at fixed mass and environment - the
star formation histories of galactic bulges and pure spheroids are
indistinguishable, and difficult to reconcile with the picture whereby the
majority of large bulges form primarily via secular processes within spiral
galaxies.Comment: 5 pages, 3 figures, accepted for publication in ApJ Letter
