Subaru deep survey I. Near-infrared observations

Deep near-infrared images of a blank 2′ × 2′ section of sky near the galactic north pole taken by Subaru Telescope are presented. The total integration times of the J and K′ bands were 12.1 hr and 9.7 hr, resulting in 5 σ limiting magnitudes of 25.1 and 23.5 mag, respectively. The numbers of sources within these limiting magnitudes found with an automated detection procedure are 385 in the J band and 350 in K′. Based on photometric measurements of these sources, we present number count vs. magnitude relations, color vs. magnitude diagrams, size vs. color relationships, etc. The slope of the galaxy number count plotted against the AB magnitude scale is about 0.23 in the 22 to 26 AB magnitude range of both bands. The spatial number density of galaxies as well as the slopes in the faint-end region given by the Subaru Deep Field (SDF) survey are consistent with those given by HST-NICMOS surveys, as expressed on the AB magnitude diagram. Several sources having very large J - K′ color have been found, including a few K′ objects without detection at J. In addition, a number of faint galactic stars were also detected, most of which are assigned to M-subdwarfs, together with a few brown dwarf candidates.