Emission-line properties of MG 2016+112: A luminous obscured quasar at high redshift

Abstract

We present new high signal-to-noise ratio spectra of the components B and C of the gravitational lensing system MG 2016+112. We show that image C displays strong emission lines of Lyα, NV, CIV, HeII, and CIII] redshifted to z = 3.27, similar to images A and B. We examine the emission-line flux ratios in order to put constraints on the lens models as well as to investigate the intrinsic nature of MG 2016+112. The observed line ratios of B and C are consistent with those expected in the simple photo-ionization models for narrow-line region of active galactic nuclei (AGN) except for the enhanced NV lines. The line ratios difference of components B and C can be interpreted as a difference in ionization parameters. This result is consistent with lens model prediction that C is a fold image of a slightly outer part of the nucleus. MG 2016+112 is known to be very unique among the high-redshift AGN; it is neither an ordinary broad-line quasar nor a powerful radio galaxy as indicated by the width and flux ratio of the emission lines. Together with other observed properties discussed in literature, we argue that MG 2016+112 may be an obscured luminous radio-quiet quasar.