THE HIDDEN NUCLEAR-SPECTRUM OF THE LUMINOUS IRAS SOURCE FSC10214+4724

Optical spectropolarimetry of the luminous IRAS source FSC 10214 + 4724 (z = 2.286) reveals that the strong (approximately 17%) linear polarization detected by Lawrence et al. is shared by both the narrow UV emission lines and the underlying continuum. This observation and the brightness of the source rule out synchrotron emission and dichroic extinction by dust as the polarizing mechanism, leaving scattering as the only plausible cause of the polarized emission. The narrowness of the lines requires that the scatterers be dust grains or cool (below 1.6 x 10(4) K) electrons. We can recover the spectrum that is incident on the scattering medium provided we make some reasonable assumptions regarding the source geometry. The scattered UV spectrum has a power-law index alpha of -1.2 +/- 0.6 (F(nu) is-proportional-to nu(alpha)), steeper than would be expected from a young burst of star formation but similar to that of many AGNs.