A Gravitational Lens Solution for IRAS F10214+4724

Abstract

We show that the high redshift IRAS source F10214 is highly magnified by the gravitational field of an intervening elliptical galaxy, accounting for its many anomalous properties. Detailed radio and near-IR images identify the IRAS source with a symmetric arc, centered on a red object, or lensing galaxy. To explain the observed structures, the center of the source must much more highly magnified than its outer regions. Lensing predicts a small counterimage to the arc, which we find adjacent to the lensing galaxy. A red component in the observed spectrum suggests a lens redshift of unity, and the lens model yields a mass estimate of $M(r<3kpc)\approx10^{11}{M_solar}$, consistent with an ordinary elliptical galaxy. We present new high-resolution optical images which show a thin arc of emission, implying an intrinsically small source ($<0.5kpc$) which is highly magnified ($\sim20\times$). Since the optical is strongly polarized with a Seyfert~II spectrum, we propose that the optical arc is magnified image of the inner region of an obscured AGN. The obscuring ``torus'' will be similarly magnified, naturally accounting for the large IR flux. We show that finding objects like F10214+4724 in redshift surveys is probable, given the level of magnification bias expected for compact luminous IRAS sources. Such cases represent the obscured AGN counterparts to the lensed QSO population and, because of their extended sizes, are useful in determining the mass distribution in the lensing galaxies.