NEAR-INFRARED IMAGING OF THE PROPOSED Z=2 CLUSTER BEHIND CL-0939-851)(4713 (ABELL)

We have obtained deep J and K' images of a 90-arcsec square field cont aining the z = 2.0 QSO that is viewed through the z = 0.4 rich cluster A851. Brightnesses of individual galaxies are measured from these dat a, and archival F702W WFPC2 images from HST. The results are used to c onstruct two-color diagrams, color-magnitude diagrams, and luminosity functions of galaxies in A851 and the faint objects discovered by Dres sier et al. (1993, AQJ, 404, L45) near the QSO. The QSO faint companio ns appear to form a separate population from other faint galaxies in t he field. Comparisons with the GISSEL models covering redshifts from 0 to 3 indicate that (1) the A851 galaxies have ages between 3 and 10 G yr, and (2) if they are at the QSO redshift, the QSO companion galaxie s are within 1 Gyr of cessation of star formation.