The infrared Einstein ring in the gravitational lens MG J1131 + 0456 and the death of the dusty lens hypothesis

We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131 + 0456, which show that its lens galaxy is an H = 18.6 mag, transparent, early-type galaxy at a redshift of z_l ≃ 0.84; it has a major axis effective radius R_e = 0″.7 ± 0″.1, projected axis ratio b/a = 0.6 ± 0.1, and major axis P.A. = 55° ± 9°. The lens is the brightest member of a group of at least seven galaxies with similar R-I and I-H colors, and the two closest group members produce sufficient tidal perturbations to explain the shape of the ring. The host galaxy of the MG J1131 + 0456 source is a z_s ≳ 2 extremely red object (ERO) that is lensed into optical and infrared rings of dramatically different morphologies. These differences imply a strongly wavelength-dependent source morphology that could be explained by embedding the host in a larger, dusty disk. At 1.6 μm (H), the ring is spectacularly luminous, with a total observed flux of H = 17.4 mag and a demagnified flux of 19.3 mag, corresponding to a 1-2 L* galaxy at the probable source redshift of z_s ≳ 2. Thus, it is primarily the stellar emission of the radio source host galaxy that produces the overall colors of two of the reddest radio lenses, MG J1131 + 0456 and JVAS B1938 + 666, aided by the suppression of optical active galactic nucleus emission by dust in the source galaxy. The dusty lens hypothesis - that many massive early-type galaxies with 0 ≲ z_l ≲ 1 have large, uniform dust opacities - is ruled out.