Letter to the Editor
Lensing galaxies: light or dark?
N. Jackson 1,
P. Helbig 1,
I. Browne 1,
C.D. Fassnacht 2,
L. Koopmans 3,
D. Marlow 1 and
P.N. Wilkinson 1
Received 22 January 1998 / Accepted 24 February 1998
In a recent paper, Hawkins (1997) argues on the basis of statistical studies of double-image gravitational lenses and lens candidates that a large population of dark lenses exists and that these outnumber galaxies with more normal mass-to-light ratios by a factor of 3:1. If correct, this is a very important result for many areas of astronomy including galaxy formation and cosmology. In this paper we discuss our new radio-selected gravitational lens sample, JVAS/CLASS, in order to test and constrain this proposition. We have obtained ground-based and HST images of all multiple-image lens systems in our sample and in 12 cases out of 12 we find the lensing galaxies in the optical and/or near infrared. Our success in finding lensing galaxies creates problems for the dark lens hypothesis. If it is to survive, ad hoc modifications seem to be necessary: only very massive galaxies () can be dark, and the cutoff in mass must be sharp. Our finding of lens galaxies in all the JVAS/CLASS systems is complementary evidence which supports the conclusion of Kochanek et al. (1997) that many of the wide-separation optically-selected pairs are physically distinct quasars rather than gravitational lens systems.
Key words: galaxies: fundamental parameters cosmology: dark matter gravitational lensing
© European Southern Observatory (ESO) 1998
Online publication: May 15, 1998