Title: The abundance of compact quiescent galaxies since z ~ 0.6,
Abstract: We set out to quantify the number density of quiescent massive compact
galaxies at intermediate redshifts. We determine structural parameters based on
i-band imaging using the CFHT equatorial SDSS Stripe 82 (CS82) survey (~170 sq.
degrees) taking advantage of an exquisite median seeing of ~0.6''. We select
compact massive (M > 5x10^10 M_sun) galaxies within the redshift range of
0.2<z<0.6. The large volume sampled allows to decrease the effect of cosmic
variance that has hampered the calculation of the number density for this
enigmatic population in many previous studies. We undertake an exhaustive
analysis in an effort to untangle the various findings inherent to the diverse
definition of compactness present in the literature. We find that the absolute
number of compact galaxies is very dependent on the adopted definition and can
change up to a factor of >10. We systematically measure a factor of ~5 more
compacts at the same redshift than what was previously reported on smaller
fields with HST imaging, which are more affected by cosmic variance. This means
that the decrease in number density from z ~ 1.5 to z ~ 0.2 might be only of a
factor of ~2-5, significantly smaller than what previously reported. This
supports progenitor bias as the main contributor to the size evolution. This
milder decrease is roughly compatible with the predictions from recent
numerical simulations. Only the most extreme compact galaxies, with Reff <
1.5x( M/10^11 M_sun)^0.75 and M > 10^10.7 M_sun, appear to drop in number by a
factor of ~20 and hence likely experience a noticeable size evolution.