  We investigate in detail 13 early-type field galaxies with 0.2<z<0.7 drawn
from the FORS Deep Field. Since the majority (9 galaxies) is at z~0.4, we
compare the field galaxies to 22 members of three rich clusters with z=0.37 to
explore possible variations caused by environmental effects. We exploit
VLT/FORS spectra (R~1200) and HST/ACS imaging to determine internal kinematics,
structures and stellar population parameters. From the Faber-Jackson and
Fundamental Plane scaling relations we deduce a modest luminosity evolution in
the B-band of 0.3-0.5mag for both samples. We compare measured Lick absorption
line strengths (Hdelta, Hgamma, Hbeta, Mg_b, & Fe5335) with evolutionary
stellar population models to derive light-averaged ages, metallicities and the
element abundance ratios Mg/Fe. We find that all these three stellar parameters
of the distant galaxies obey a scaling with velocity dispersion (mass) which is
very well consistent with the one of local nearby galaxies. In particular, the
distribution of Mg/Fe ratios of local galaxies is matched by the distant ones,
and their derived mean offset in age corresponds to the average lookback time.
This indicates that there was little chemical enrichment and no significant
star formation within the last ~5Gyr. The calculated luminosity evolution of a
simple stellar population model for the derived galaxy ages and lookback times
is in most cases very consistent with the mild brightening measured by the
scaling relations.
