The Cosmic Horseshoe: Discovery of an Einstein Ring around a Giant Luminous Red Galaxy

Belokurov, V.; Evans, N. W.; Moiseev, A.;King, L. J.; Hewett, P. C.; Pettini, M.;Wyrzykowski, L.; McMahon, R. G.; Smith, M. C.;Gilmore, G.; Sanchez, S. F.; Udalski, A.;Koposov, S.; Zucker, D. B.; Walcher, C. J.. The Cosmic Horseshoe: Discovery of an Einstein Ring around a Giant Luminous Red Galaxy. The Astrophysical Journal. 2007, Vol. Volume 671, Issue 1, pp. L9-L12., p. -2007.

We report the discovery of an almost complete (~300°) Einstein ring of diameter 10'' in Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). Spectroscopic data from the 6 m telescope of the Special Astrophysical Observatory reveal that the deflecting galaxy has a line-of-sight velocity dispersion in excess of 400 km s-1 and a redshift of 0.444, while the source is a star-forming galaxy with a redshift of 2.379. From its color, luminosity, and velocity dispersion, we argue that this is the most massive galaxy lens hitherto discovered.