Morphology of the triple QSO PG1115 + 08

Abstract

Weymann et al.¹ have reported that two faint unresolved objects located within 3arcs of the QSO PG1115 + 08 have also the same spectra. The emission lines of C III λl,909 and C IV λ1,549 at a redshift of 1.72 have central wavelengths and profiles that are indistinguishable between the objects. It is inferred that the three objects are likely to be images of the same QSO produced by intervening matter acting as a gravitational lens. Only one other example of such an effect is known, that is the double QSO 0957 + 56A,B. In this case, the two QSO images are of roughly equal magnitude ( V∼17) and separated by 6 arc s. A plate obtained in excellent seeing by Stockton² shows an intervening galaxy at z = 0.4 lying about 1 arc s from one of the QSO images. The present observations were undertaken to search for evidence of an intervening galaxy in PG1115 + 08, appearing either directly in a deep image, or as a difference in colour between components, and also to look for any structure in the three images. A colour difference could arise, as was the case for the double QSO, if a galaxy is nearly coincident with one of the QSO images.