We present the results of near-infrared imaging observations of the galaxy overdensity around the z = 1.44 radio-loud active galactic nucleus (AGN) 6CE1100+3505, which was carried out with the purpose of sampling the redshifted Hα emission from the actively star-forming galaxies that could constitute the overdensity. The existence of the structure around this AGN was spectroscopically confirmed by previous grism observations which are however limited to the central region. Using the CH4Off narrow/medium-band and H broad band filters in the Wide Infrared Camera (WIRCam) on the Canada-France-Hawaii Telescope (CFHT), we constructed a sample of objects that show a flux excess in the CH4Off band due to line emission. The emission line flux is ∼ 4.9 × 10−16 erg s−1 cm−2 , corresponding to a star formation rate (SFR) of ∼ 50 M⊙ yr−1 for galaxies at redshifts z ∼ 1.4. None of the galaxies with medium-band flux excess is located within 1 Mpc from the central AGN, and there is no evidence that the selected galaxies are associated with the proposed cluster. Along with the star formation quenching near the center that was found from the previous grism observations, the lack of extreme starbursts in the structure suggests that at z ∼ 1.4, overdense regions are no longer favorable locations for vigorous star formation.

Abstract
    1. INTRODUCTION
    2. DATA
    3. POTENTIAL LINE EMITTERS
    4. PROPERTIES OF z ~ 1:4 Hα EMITTERS
    5. SUMMARY
    REFERENCES

• Hyunjin Shim(Department of Earth Science Education, Kyungpook National University)
• Jong Chul Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Narae Hwang(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Byeong-Gon Park(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)