The galaxy cluster is an important object for investigating the large scale structure and evolution of galaxies. Recent wide and deep near-IR surveys provide an opportunity to search for galaxy clusters in the high redshift universe. We have identified candidate clusters of 0.8< z <1.2 from the 25 deg2 SA22 field using an optical-near-IR dataset from merged UKIDSS DXS, IMS and CFHTLS catalogs. Using these candidates, we investigate the star forming activity of member galaxies. Consequently, at z ~1, the star forming activity of cluster galaxies is not distinguishable from those of field galaxies, which is different from members in local clusters. This means the environmental effect becomes more important for M* > 1010M⊙ galaxies at z <1.

ABSTRACT
1. INTRODUCTION
2. DATA AND METHODOLOGY
3. STAR FORMING ACTIVITY OF MEMBERS
4. SUMMARY
REFERENCES

• Jae-Woo Kim(Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, Seoul National University)
• Myungshin Im(Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, Seoul National University)
• Seong-Kook Lee(Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, Seoul National University)
• Minhee Hyun(Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, Seoul National University)