NEAR-INFRARED JHK PHOTOMETRY OF INTERMEDIATE REDSHIFT CLUSTERS

Deep near-infrared images of four intermediate redshift (z=0.2-0.4) cl usters (Abell 370, Abell 963, CL 0024+1654, and CL 0909+4408) have bee n obtained in the J, H, and K' bands using the UCLA Two-Channel IR Cam era, with a spatial resolution of similar to 1''. The 3'X3' field of v iew includes over 100 galaxies in each cluster. Photometry has been ob tained with 1 sigma limiting magnitudes of 21.7 at J, 21.0 at H, and 2 0.4 at K', and complete to 2 magnitudes fainter than L. Data reductio n techniques for flat-fielding, object identification, and photometry of faint object crowded fields are discussed. The best method is the s ubtraction of a running-average sky made from object frames. The photo metry is cross referenced to previous catalogs, and infrared color-mag nitude diagrams are presented. Comparison of the IR colors of these fo ur clusters to the predictions of the spectral synthesis models of Bru zual and Chariot is discussed. There is a discrepancy between the mode ls 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 ga laxy at z>1. (C) 1996 American Astronomical Society.