THE SEYFERT-II NATURE OF THE IRAS SOURCE FSC-10214+4724

We have observed the rest-frame optical and UV spectra of the luminous, high redshift IRAS source FSC 10214 + 4724. We find the optical emission lines to be characterized by ratios similar to those found in Seyfert II galaxies. We support the conclusion of previous work that the UV emission lines are similar to those attributed to AGN rather than to star formation. The ratio Halpha/Hbeta greater-than-or-equal-to 20 (2sigma lower limit) implies substantial reddening of the narrow line region with A(V) > 5.5, sufficient to hide a broad line region in our Halpha observations. Given this large inferred reddening and the strength of the UV continuum and emission lines, we conclude (as have others) that simple screen models of reddening are not appropriate for this object. These properties are very similar to those of the infrared luminous galaxies at lower redshift, suggesting that FSC 10214 + 4724 is the luminous extreme of the same population. We also present H band (1.6 mum) imaging polarimetry observations and find that the rest-frame optical emission is unpolarized (P = 3.2% +/- 2.0%). This deep image of the field shows FSC 10214 + 4724 to possess an unresolved core, with several companions located within 10'' of the point source. We find it unlikely that this group of objects is physically associated with FSC 10214 + 4724 at z = 2.3, and we argue that their magnitudes and colors are more consistent with those expected for galaxies in a foreground group. While galaxy number counts would suggest that such a projection has a low probability of being observed randomly, a foreground group might gravitational lens the z = 2.3 source, making such random statistics inappropriate, and contribute to the large observed luminosity of FSC 10214 + 4724. Comparison of H band images taken on two occasions one year apart show that FSC 10214 + 4724 had varied by 0. 16 +/- 0.03 mag relative to a nearby star during that time. The UV-optical emission line spectra, the bright dereddened continuum magnitude (K less-than-or-equal-to 12) of the unresolved core, its extremely large bolometric luminosity, strong UV polarization, and possible variability all suggest that FSC 10214 + 4724 harbors an obscured AGN. Given that we observe no spectral features attributable to star formation, it appears either that star formation in FSC 10214 + 4724 is more highly obscured at optical and UV wavelengths than the narrow line region of the AGN, or that the AGN (rather than star formation) dominates the large luminosity of this object.