3 Micron Imaging of the Hubble Deep Field

Abstract

Images of the Hubble Deep Field (HDF) at 3.2 μm, taken with the 10 m Keck Telescope, are presented. The images cover a total area of ~2.5 arcmin². To a 5 σ limit of [3.2]_tot~17.5 mag (Vega relative), 11 sources are detected, nine of which are extragalactic. The integrated galaxy number counts are therefore ~1.3x10⁴ deg^-2 to this depth. The galaxies detected at 3.2 μm have a median redshift of z=0.56. All 3.2 μm sources have 1.6 μm, 1.1 μm, and visual counterparts, all of fairly regular morphology; several also have 6.7 μm, 15 μm, 850 μm, 8.5 GHz, or 1.4 GHz counterparts. No sources are found that are either anomalously red or anomalously blue in their H-[3.2] color, and there are significant detections of most of the known near-infrared HDF sources for which detection in these 3.2 μm data seemed likely. Based on observations made at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California, and with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.