The double quasar Q2138-431: lensing by a dark galaxy?
Abstract
We report the discovery of a new gravitational lens candidate Q2138-431AB, comprising two quasar images at a redshift of 1.641, separated by 4.5 arcsec. The spectra of the two images are very similar, and the redshifts agree to better than 115 km s^-1. The two images have magnitudes B_J=19.8 and 21.0, and, in spite of a deep search and image subtraction procedure, no lensing galaxy has been found with R<23.8. Modelling of the system configuration implies that the mass-to-light ratio of any lensing galaxy is likely to be around 1000 Msolar/Lsolar, with an absolute lower limit of 200 Msolar/Lsolar for an Einstein-de Sitter universe. We conclude that the most likely explanation of the observations is gravitational lensing by a dark galaxy, although it is possible we are seeing a binary quasar.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 1997
- DOI:
- 10.1093/mnras/291.4.811
- arXiv:
- arXiv:astro-ph/9709049
- Bibcode:
- 1997MNRAS.291..811H
- Keywords:
-
- Quasars;
- Gravitational Lenses;
- Galaxies;
- Red Shift;
- Halos;
- Astrophysics;
- GALAXIES: HALOES;
- QUASARS: INDIVIDUAL: Q2138-431;
- GRAVITATIONAL LENSING;
- Astrophysics
- E-Print:
- 17 pages (Latex), 8 postscript figures included, accepted by MNRAS