We report on the identification of the old stellar population galaxy candidates at z \gtrsim 5 .
We developed a new infrared color selection scheme to isolate galaxies with the strong Balmer breaks at z \gtrsim 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 \gtrsim 5 .
Their stacked spectral energy distribution is fitted well with the old stellar population template with M _ { * } = ( 7.5 \pm 1.5 ) \times 10 ^ { 10 } M _ { \odot } , star formation rate = 0.9 \pm 0.2 M _ { \odot } yr ^ { -1 } , dust A _ { V } < 1 , and age = 0.7 \pm 0.4 Gyr at z = 5.7 \pm 0.6 , where the dusty star-forming galaxies at z \sim 2.8 is disfavored because of the faintness in the 24 \mu m. The stellar mass density of these evolved galaxy candidates , ( 6 \pm 4 ) \times 10 ^ { 4 } M _ { \odot } 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 \sim 6 .