A spectroscopic study of IRAS F10214+4724

The z 1⁄4 2:286 IRAS galaxy F10214 þ 4724 remains one of the most luminous galaxies in the Universe, despite its gravitational lens magnification. We present optical and near-infrared spectra of F10214 þ 4724, with clear evidence for three distinct components: lines of width ,1000 km s from a Seyfert 2 nucleus; & 200 km s lines which are likely to be associated with star formation; and a broad (,4000 km s) C III] 1909-Å emission line which is blueshifted by ,1000 km s with respect to the Seyfert 2 lines. Our study of the Seyfert 2 component leads to several new results. (i) From the double-peaked structure in the Lya line, and the lack of Lyb, we argue that the Lya photons have emerged through a neutral column of NH , 2:5 × 10 m, possibly located within the AGN narrow-line region, as proposed for several high-redshift radio galaxies. (ii) The resonant O VI 1032, 1036-Å doublet (previously identified as Lyb) is in an optically thick (1:1) ratio. At face value this implies an extreme density (ne , 10 17 m) more typical of broad-line region clouds. However, we attribute this instead to the damping wings of Lyb from the resonant absorption. (iii) A tentative detection of He II 1086 suggests little extinction in the rest frame ultraviolet.