The Infrared Einstein Ring in the Gravitational Lens MG J1131+0456 and the Death of the Dusty Lens Hypothesis

Abstract

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^deg+/-9^deg. 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. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.