SPECTROSCOPY OF ARCS IN THE RICH CLUSTER ABELL-963

Spectra are presented for portions of the two arcs observed close to the dominant cD galaxy in the rich cluster Abell 963 (z = 0.206). The spectrum of the northern arc displays a strong emission line at 6600 angstrom which is seen along the entire arc. The feature cannot be understood unless the redshift is greater than that of the cluster, the most likely interpretation being [O II] 3727 angstrom at z = 0.771. The southern arc is considerably fainter and its spectrum shows no obvious features. However, new CCD photometry is consistent with a near-constant blue colour (B - R approximately 0.3) along both arcs supporting the suggestion that they arise from the gravitationally lensed light of a background object. The optical and infrared colour is consistent with a spiral galaxy undergoing strong star formation at this redshift. We discuss briefly the implication of this result, and the possible role lensing surveys may play in the study of high-redshift galaxies.