The Number Density of Quiescent Compact Galaxies at Intermediate
  Redshift
  Massive compact systems at 0.2<z<0.6 are the missing link between the
predominantly compact population of massive quiescent galaxies at high redshift
and their analogs and relics in the local volume. The evolution in number
density of these extreme objects over cosmic time is the crucial constraining
factor for the models of massive galaxy assembly. We select a large sample of
~200 intermediate-redshift massive compacts from the BOSS spectroscopic dataset
by identifying point-like SDSS photometric sources with spectroscopic
signatures of evolved redshifted galaxies. A subset of our targets have
publicly available high-resolution ground-based images that we use to augment
the dynamical and stellar population properties of these systems by their
structural parameters. We confirm that all BOSS compact candidates are as
compact as their high-redshift massive counterparts and less than half the size
of similarly massive systems at z~0. We use the completeness-corrected numbers
of BOSS compacts to compute lower limits on their number densities in narrow
redshift bins spanning the range of our sample. The abundance of extremely
dense quiescent galaxies at 0.2<z<0.6 is in excellent agreement with the number
densities of these systems at high redshift. Our lower limits support the
models of massive galaxy assembly through a series of minor mergers over the
redshift range 0<z<2.
