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' × 7' field of view with a pixel scale of 0”.117pixel⁻¹ in the wavelength range of 0.85 to 2.5μ using cooled optics and two 2048 × 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 Kₛ band (Vega) with $S/N$$=$ 5, 0”.5 seeing, 1”.0 aperture, and 1hr exposure.