What Are the Progenitors of Compact, Massive, Quiescent Galaxies at
  z=2.3? The Population of Massive Galaxies at z>3 from NMBS and CANDELS
  [Abridged] Using public data from the NMBS and CANDELS surveys, we study the
population of massive galaxies at z>3 to identify the potential progenitors of
z~2 compact, massive, quiescent (CMQ) galaxies, furthering our understanding of
the evolution of massive galaxies. Our work is enabled by high-resolution
CANDELS images and accurate photometric redshifts, stellar masses and star
formation rates (SFRs) from 37-band NMBS photometry. The total number of z>3
massive galaxies is consistent with the number of massive quiescent (MQ)
galaxies at z~2, implying that the SFRs for all of these galaxies must be much
lower by z~2. We discover 4 CMQ galaxies at z>3, pushing back the time for
which such galaxies have been observed. However, the volume density for these
galaxies is significantly less than that of galaxies at z<2 with similar
masses, SFRs, and sizes, implying that additional CMQ galaxies must be created
in the ~1 Gyr between z=3 and z=2. We find 5 star-forming galaxies at z~3 that
are compact (Re<1.4 kpc) and have stellar mass M*>10^(10.6)Msun, likely to
become members of the CMQ galaxy population at z~2. We evolve the stellar
masses and SFRs of each individual z>3 galaxy adopting 5 different star
formation histories (SFHs) and studying the resulting population of massive
galaxies at z=2.3. We find that declining or truncated SFHs are necessary to
match the observed number density of MQ galaxies at z~2, whereas a constant SFH
results in a number density significantly smaller than observed. All of our
assumed SFHs imply number densities of CMQ galaxies at z~2 that are consistent
with the observed number density. Better agreement with the observed number
density of CMQ galaxies at z~2 is obtained if merging is included in the
analysis and better still if star formation quenching is assumed to shortly
follow the merging event, as implied by recent models of formation of MQ
galaxies.
