2018ApJ...861...86M

We present high angular resolution imaging (23.9 x 11.3 mas, 138.6 x 65.5 pc) of the radio-loud quasar PSO J352.4034-15.3373 at z = 5.84 with the Very Long Baseline Array (VLBA) at 1.54 GHz. This quasar has the highest radio-to-optical flux density ratio at such a redshift, making it the radio-loudest source known to date at z ∼ 6. The VLBA observations presented here resolve this quasar into multiple components with an overall linear extent of 1.62 kpc (0.''28) and with a total flux density of 6.57 ± 0.38 mJy, which is about half of the emission measured at a much lower angular resolution. The morphology of the source is comparable with either a radio core with a one-sided jet or a compact or a medium-size symmetric object (CSO/MSO). If the source is a CSO/MSO, and assuming an advance speed of 0.2c, then the estimated kinematic age is ∼10⁴ years.