  Most massive passive galaxies are compact at high redshifts, but similarly
compact massive galaxies are rare in the local universe. The most common
interpretation of this phenomenon is that massive galaxies have grown in size
by a factor of about five since redshift z=2. An alternative explanation is
that recently quenched massive galaxies are larger (a "progenitor bias"). In
this paper we explore the importance of progenitor bias by looking for
systematic differences in the stellar populations of compact early-type
galaxies in the DEEP2 survey as a function of size. Our analysis is based on
applying the statistical technique of bootstrap resampling to constrain
differences in the median ages of our samples and to begin to characterize the
distribution of stellar populations in our co-added spectra. The light-weighted
ages of compact early-type galaxies at redshifts 0.5 < z < 1.4 are compared to
those of a control sample of larger galaxies at similar redshifts. We find that
massive compact early-type galaxies selected on the basis of red color and high
bulge-to-total ratio are younger than similarly selected larger galaxies,
suggesting that size growth in these objects is not driven mainly by progenitor
bias, and that individual galaxies grow as their stellar populations age.
However, compact early-type galaxies selected on the basis of image smoothness
and high bulge-to-total ratio are older than a control sample of larger
galaxies. Progenitor bias will play a significant role in defining the apparent
size changes of early-type galaxies if they are selected on the basis of the
smoothness of their light distributions.
