A gravitational lens candidate with an unusually red optical counterpart

In a radio and optical program aimed at identifying gravitational lens candidates, we have discovered that the strong radio source, MG0414+0534, displays many of the properties expected in a gravitational lens system. At radio wavelengths and 0.5″ resolution, MG0414+0534 is made up of four compact components whose unusual configuration and relative flux densities are similar to those found in confirmed four-image gravitational lens systems. At optical wavelengths (with ≲1″ seeing) we detect three objects, consistent with there being optical objects at the positions of the radio components, given the lower optical resolution. The radio and optical centroid positions agree within the astrometric errors, and the relative ordering of the fluxes is the same. The colors and radio-optical spectral indices are similar, but there are differences larger than the photometric errors and the measured variability (∼30%). The optical properties of the objects are unusual, and do not fit any conventional active galactic nucleus classification scheme. All three optical objects are exceedingly red, with R-I instrumental colors about 1.5 magnitudes redder than a nearby M star. A spectrum, in the wavelength range 4333-9793 Å, of the combined light of the two brighter objects displays a power law continuum, with spectral index α = 9 (f_v∝v^-α). There are no emission lines, and only one securely detected broad absorption line; therefore, the redshifts of the objects are as yet unknown. There is, as yet, no convincing evidence for light from a lensing galaxy or galaxies. If MG0414+0534 is a gravitational lens, this implies either a large lens mass-to-light ratio, a large source redshift, or the presence of significant extinction. Extinction by dust might simultaneously explain the unusually red color and the absence of light from a lens. Since the galactic latitude of MG0414+0534 is -31°, such dust is unlikely to be found along the line of sight within the Galaxy.