High Resolution Observations of IRAS FSC10214: A z=2.3 gravitationally lensed starburst/AGN

We present new radio data of IRAS FSC10214, a gravitationally lensed starburst/AGN composite galaxy at z=2.3. Our Bayesian MCMC source plane reconstruction places what we argue to be the AGN core (VLA 8 GHz) and the scattered quasar light (HST rest-frame ultraviolet) at an angle perpendicular to the ultraviolet polarisation angle. The size of and projected distance to the dominant HST UV emission component is roughly consistent with the smooth polarisation angle variation observed with HST polarimetry, suggesting that the modelled offset between these two components is reasonably accurate. Both of these components lie inside a larger 1.6 GHz component (observed with MERLIN) thought to be dominated by a radio lobe based on its steep radio spectrum but very likely to include star formation as well given the substantial molecular mass (M_H2 ~ 10¹² µ⁻¹ M) in this system. Our lens model finds the HST rest-frame UV component is preferentially magnified due to its closer proximity to the cusp of the caustic. A preferential magnification of the narrow line region dust clouds, where the ultraviolet scattering is assumed to occur, supports previous claims that differential magnification could mask the expected polycyclic aromatic hydrocarbon spectral features in the Spitzer mid-infrared spectrum which broadly trace the star forming regions. fu¨rther predictions will be tested with upcoming EVN and VLBA observations.