Possible identification of massive and evolved galaxies At z > 5
  We report on the identification of the old stellar population galaxy
candidates at z > 5. We developed a new infrared color selection scheme to
isolate galaxies with the strong Balmer breaks at z > 5, and applied it to the
ultra-deep and wide infrared survey data from the Spitzer Extended Deep Survey
(SEDS) and the UKIRT Infrared Deep Sky Survey. The eight objects satisfying K -
[3.6] > 1.3 and K - [3.6] > 2.4 ([3.6] - [4.5]) + 0.6 are selected in the 0.34
deg^2 SEDS Ultra Deep Survey field. Rich multi-wavelength imaging data from
optical to far-infrared are also used to reject blending sources and strong
nebular line emitters, and we finally obtained the three most likely evolved
galaxies at z > 5. Their stacked spectral energy distribution is fitted well
with the old stellar population template with M_{*} = (7.5+-1.5) x 10^{10}
Msun, star formation rate = 0.9 +- 0.2 Msun yr^{-1}, dust A_V < 1, and age =
0.7+-0.4 Gyr at z = 5.7+-0.6, where the dusty star-forming galaxies at z ~ 2.8
are disfavored because of the faintness in the 24um. The stellar mass density
of these evolved galaxy candidates, (6+-4) x 10^4 Msun Mpc^{-3}, is much lower
than that of star-forming galaxies, but the non-zero fraction suggests that
initial star-formation and quenching have been completed by z ~ 6.
