Luminous and High Stellar Mass Candidate Galaxies at z ~ 8 Discovered in
  CANDELS
  One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep
Extragalactic Legacy Survey is to track galaxy evolution back to z ~ 8. Its
two-tiered "wide and deep" strategy bridges significant gaps in existing
near-infrared surveys. Here we report on z ~ 8 galaxy candidates selected as
F105W-band dropouts in one of its deep fields, which covers 50.1 square arcmin
to 4 ks depth in each of three near-infrared bands in the Great Observatories
Origins Deep Survey southern field. Two of our candidates have J<26.2 mag, and
are > 1 mag brighter than any previously known F105W-dropouts. We derive
constraints on the bright-end of the rest-frame ultraviolet luminosity function
of galaxies at z ~ 8, and show that the number density of such very bright
objects is higher than expected from the previous Schechter luminosity function
estimates at this redshift. Another two candidates are securely detected in
Spitzer Infrared Array Camera images, which are the first such individual
detections at z ~ 8. Their derived stellar masses are on the order of a few x
10^9 M_sun, from which we obtain the first measurement of the high-mass end of
the galaxy stellar mass function at z ~ 8. The high number density of very
luminous and very massive galaxies at z ~ 8, if real, could imply a large
stellar-to-halo mass ratio and an efficient conversion of baryons to stars at
such an early time.
