Multi-Object Infrared Camera and Spectrograph (MOIRCS) for the Subaru Telescope I. Imaging

MOIRCS is a fully cryogenic near-infrared instrument for the 8.2 m Subaru Telescope. MOIRCS has two observation modes: a wide-field imaging mode and a multiobject spectroscopy mode. This paper describes the imaging mode, its specifications, and actual performances that we confirmed through laboratory tests and commissioning observations. The imaging mode provides a 4' x 7' field of view with a pixel scale of 0 ''.117 pixel(-1) in the wave-length range of 0.85 to 2.5 mu m using cooled optics and two 2048 x 2048 HgCdTe HAWAII-2 focal plane arrays. Good-quality images are obtained over the entire field of view with practically no chromatic aberration. The limiting magnitudes for a point source estimated from observed background brightness and throughput are 23.7 in the J band, 23.0 in the H band, and 22.6 in the K-s band (Vega) with S/N = 5.0 ''.5 seeing, 1 ''.0 aperture, and 1 hr exposure.