A spectroscopic study of IRAS F10214+4724

The z = 2.286 IRAS galaxy F10214 + 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 + 4724, with clear evidence for three distinct components: lines of width similar to 1000 km s(-1) from a Seyfert 2 nucleus; less than or similar to 200 km s(-1) lines which are likely to be associated with star formation; and a broad (similar to 4000 km s(-1)) C III] 1909-Angstrom emission line which is blueshifted by similar to 1000 km s(-1) 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 Ly alpha line, and the lack of Ly beta, we argue that the Ly alpha photons have emerged through a neutral column of N-H similar to 2.5 x 10(25) m(-2), possibly located within the AGN narrow-line region, as proposed for several high-redshift radio galaxies. (ii) The resonant O VI 1032, 1036-Angstrom doubler (previously identified as Ly beta) is in an optically thick (1:1) ratio. At face value this implies an extreme density (n(e) similar to 10(17) m(-3)) more typical of broad-line region clouds. However, we attribute this instead to the damping wings of Ly beta from the resonant absorption, (iii) A tentative detection of He II 1086 suggests little extinction in the rest frame ultraviolet.