Spectrophotometry and polarimetry of the giant luminous arcs in the clusters 2244–02 and Abell 370

Abstract

Lynds and Petrosian1 have reported the discovery of very large luminous arcs in two clusters of galaxies, and there have been various conjectures2 about the nature of these unusual features. Some of these are that they are: (1) images of distant objects formed by a gravitational lens generated by the visible clusters of galaxies; (2) regions of star formation stimulated by the passage of a shock front produced by a central (now extinguished) quasistellar object; (3) light echoes of a previously bright object at the centre; or (4) long arcs of stars tidally stripped from galaxies in the clusters. Observational data have been so limited that it has not been possible to establish any clearly favoured interpretation. Here we present new observations which restrict the range of possibilities, by eliminating (2), (3) and (4), even if they do not lead to a unique interpretation.