  We investigate pure luminosity evolution models for early-type (elliptical
and S0) galaxies (i.e., no number density change or morphology transition), and
examine whether these models are consistent with observed number counts in the
B, I and K bands and redshift distributions of two samples of faint galaxies
selected in the I and K bands. The models are characterized by the star
formation time scale $\tau_{SF}$ and the time $t_{gw}$ when galactic wind blows
in addition to several other conventional parameters. We find the single-burst
model ($\tau_{SF}$=0.1 Gyr and $t_{gw}$=0.353 Gyr), which is known to reproduce
the photometric properties of early-type galaxies in clusters, is inconsistent
with redshift distributions of early-type galaxies in the field environment due
to overpredictions of galaxies at $z\gsim1.4$ even with strong extinction which
is at work until $t_{gw}$. In order for dust extinction to be more effective,
we change $\tau_{SF}$ and $t_{gw}$ as free parameters, and find that models
with $\tau_{SF}\gsim0.5$ Gyr and $t_{gw}>1.0$ Gyr can be made consistent with
both the observed redshift distributions and number counts, if we introduce
strong extinction $(E(B-V)\geq1$ as a peak value). These results suggest that
early-type galaxies in the field environment do not have the same evolutionary
history as described by the single-burst model.

Astrophysics