Multiple QSO images with arcminute splittings

Abstract

• 1. The methodology just described is adequate to rule out the gravitational lens hypothesis if narrow forbidden lines are detected with different properties, allowing accurate redshift determinations, or if the MgII emission lines show a significant shift between the pair lines of sight.

• 2. When no forbidden line is observed, and the low ionization emission lines have similar properties (redshifts, profiles), the issue is logically difficult, since spectral differences are likely to be observed due to the systematic trend for high ionization broad emission lines to be shifted with respect to low ionization lines (Gaskell 1982, Wilkes 1984). Q1146+111 B and C images are a good example (Turner et al. 1986, Turner 1986). For such ambiguous cases, broad and narrow band deep CCD exposures of a few arcminute square field around the multiple QSO images may supplement efficiently the spectroscopic studies of the QSO nuclei, by searching for a candidate cluster of galaxies associated with the QSOs.

• 3. In addition to these observations, there is growing evidence that QSO clustering may occur over a wide range of angular separations (Bahcall et al. 1986, Djorgovski et al. 1987). Further observations on this phenomenon should provide clues to the formation of large scale structures at high redshift.

I gratefully acknowledge the KPNO staff, and Richard Dreiser of Yerkes Observatory for technical assistance. I especially thank Richard Kron for his help in obtaining the observational data, and for support of this project.