HS 1216+5032: a physical quasar pair with one radio-loud broad absorption line quasar

Abstract

We report on new multiwavelength observations of HS 1216+5032, a pair of quasi-stellar objects (QSOs) at z = 1.45 separated by 9.1 arcsec, which has been a perennial candidate for a massive dark lens. We explore high signal-to-noise ratio optical spectra from the MMT of both components, which show that aside from the effects of absorption, the emission-line profiles are quite similar. Near-infrared spectra from the United Kingdom Infrared Telescope show identical velocities in Ha emission, but a significant difference in the strength of the narrow component, which is difficult to explain in a lens scenario. We highlight that, based on data from the Very Large Array Faint Images of the Radio Sky survey, HS 1216+5032B is a radio-loud broad absorption line QSO, which certifies HS 1216+5032 as a physical quasar pair. Intriguingly, both quasars show spectroscopic evidence for high accretion rates and large Eddington ratios L/L Edd , supporting the hypothesis that close galaxy interactions trigger nuclear activity.