ar X iv : a st ro - p h / 97 09 04 9 v 1 5 S ep 1 99 7 The Double Quasar Q 2138 - 431 : Lensing by a Dark Galaxy ?
نویسنده
چکیده
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 arcsecs. The spectra of the two images are very similar, and the redshifts agree to better than 115 km.sec. The two images have magnitudes BJ = 19.8 and BJ = 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 1000M⊙/L⊙, with an absolute lower limit of 200M⊙/L⊙ 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.
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