Discovery of the most distant double-peaked emitter at z = 1.369

We report the discovery of themost distant double-peaked emitter, CXOECDFS J033115.0-275518, at z = 1.369.A Keck/DEIMOS spectrum shows a clearly double-peaked broad Mgii λ2799 emission line, with FWHM ≈ 11, 000 km s^-1 for the line complex. The line profile can be well fitted by an elliptical relativistic Keplerian disk model. This is one of a handful of double-peaked emitters known to be a luminous quasar, with excellent multiwavelength coverage and a high-quality X-ray spectrum. CXOECDFS J033115.0-275518 is a radio-loud quasar with two radio lobes (FR ii morphology) and a radio loudness of f_{5 GHz}/f_4400Å ≈ 429. The X-ray spectrum can be modeled by a power law with photon index 1.72 and no intrinsic absorption; the rest-frame 0.5-8.0 keV luminosity is 5.0 ×10⁴⁴ erg s^-1. The spectral energy distribution (SED) of CXOECDFS J033115.0-275518 has a shape typical for radio-loud quasars and double-peaked emitters at lower redshift. The local viscous energy released from the line-emitting region of the accretion disk is probably insufficient to power the observed line flux, and external illumination of the disk appears to be required. The presence of a big blue bump in the SED along with the unexceptional X-ray spectrum suggest that the illumination cannot arise from a radiatively inefficient accretion flow.