Two New Large Separation Gravitational Lenses from SDSS

We present discovery images, together with follow-up imaging and spectroscopy, of two large separation gravitational lenses found by our survey for wide arcs (the CASSOWARY). The survey exploits the multicolour photometry of the Sloan Digital Sky Survey to find multiple blue components around red galaxies. CASSOWARY 2 (or “the Cheshire Cat”) is composed of two massive early-type galaxies at z = 0.426 and 0.432 respectively lensing two background sources, the first a star-forming galaxy at z = 0.97 and the second a high redshift galaxy (z > 1.4). There are at least three images of the former source and probably four or more of the latter, arranged in two giant arcs. The mass enclosed within the larger arc of radius ∼ 11 is ∼ 33 × 1012 M⊙. CASSOWARY 3 comprises an arc of three bright images of a z = 0.725 source, lensed by a foreground elliptical at z = 0.274. The radius of the arc is ∼ 4 and the enclosed mass is ∼ 2.5 × 1012 M⊙. Together with earlier discoveries like the Cosmic Horseshoe and the 8 O’Clock Arc, these new systems, with separations intermediate between the arcsecond separation lenses of typical strong galaxy lensing and arcminute separation cluster lenses, probe the very high end of the galaxy mass function.