Observations of the blue arcs in Abell 963

Abstract

Initial spectroscopic observations of the two blue arcs in Abell 963 show no evidence for strong emission lines, though continuum radiation has been detected. Since these arcs are likely the result of gravitational lensing, this observation puts several constraints on the nature of the lensed object. The lack of any broad emission lines limits the possibility of the lensed object being a QSO unless it is at a redshift of greater than 5. If the lensed object is a galaxy with [O II] λ3727 emission, as might be expected from the arc color, the galaxy must be at a redshift of greater than 0.9. The lack of Lyman α emission constrains the redshift to be less than 2.5.