Near Infrared JHK Photometry of Intermediate Redshift Clusters

Deep near-infrared images of four intermediate redshift (z = 0.2-0.4) clusters (Abell 370, Abell 963, CL 0024+1654, and CL 0909+4408) have been obtained in the J, H, and K' bands using the UCLA Two-Channel IR Camera, with a spatial resolution of ~1". The 3' x 3' field of view includes over 100 galaxies in each cluster. Photometry. has been obtained with 1 σ limiting magnitudes of 21.7 at J, 21.0 at H, and 20.4 at K', and complete to 2 magnitudes fainter than L^*^. Data reduction techniques for flat-fielding, object identification, and photometry of faint object crowded fields are discussed. The best method is the subtraction of a running-average sky made from object frames. The photometry is cross referenced to previous catalogs, and infrared color-magnitude diagrams are presented. Comparison of the IR colors of these four clusters to the predictions of the spectral synthesis models of Bruzual and Charlot is discussed. There is a discrepancy between the models and the observations of several tenths of a magnitude in the colors. Photometry has also been obtained for the gravitational lensing arcs in CL 0024+1654, which is consistent with an actively star-forming galaxy at z > 1.