Deep- and Wide-field K-band Imaging of the Subaru Deep Field: Implications for Galaxy Formation at z∼2 ^{1}

We have been carrying out K-band wide-field and deep imaging of the Subaru Deep Field (SDF) using WFCAM on UKIRT. The overlap with the optical images exceeds

700 arcmin^2 with the a limiting magnitude of ∼23.5AB. The K-band number counts of pBzKs show a "knee" around 20.5AB, which suggests the deficit of <10^{11}M_{⊙} passive galaxies at z∼1.5. This can be explained by the down-sizing evolution of galaxies, and fraction of galaxies are still under formation phase at z∼ 1.5.