SPECTROSCOPIC AND MORPHOLOGICAL EVIDENCE THAT IRAS FSC-10214+4724 IS A GRAVITATIONAL LENS

We have obtained a 0.''7 FWHM H image of IRAS FSC 10214+4724. This ima ge suggests FSC 10214+4724 is an are formed by a gravitational lens lo cated 1.''25 to the north. We have also obtained a coarse spectroscopi c continuum of the lensing galaxy. The location and strength of a brea k in the continuum suggests the 4000 Angstrom break of an early type g alaxy at a redshift of 0.42+/-0.02. A galaxy 23'' south is found to ha ve a very similar redshift of 0.429+/-0.002. This redshift, coupled wi th the observed magnitude of the lensing galaxy (H=18.45+/-0.15, in a 2'' aperture), implies the lensing galaxy has a very plausible L lumi nosity and a velocity dispersion of 210+/-20 km s(-1) (q(0)=0.5, h=0.5 ). Such a lens would produce a faint counter-are image 1.''6+/-0.''2 n orth of the main are. We observe such a counter-are in our H image, in dicating that FSC 10214+4724 is indeed gravitationally lensed. We find that lensing by a z=0.42, sigma similar to 210 km s(-1) galaxy is a v iable and probable solution to both the observed morphology and unique ly large (similar to 1x10(14) h(-2) L.) luminosity of FSC 10214+4724. The true (unlensed) nature of FSC 10214+4724 is likely an ultraluminou s IR galaxy of similar to 3.7x10(12) h(-2) L..