3 Micron Imaging of the Hubble Deep Field

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 arcmin^2. 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 ~1.3 × 10^4 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.