A VLBA-resolved Jet Associated with Super-Eddington Accretion in a Radio-loud Quasar at z = 3.4

Abstract We report the detailed jet properties of eROSITA Final Equatorial Depth Survey J084222.9+001000 (hereafter ID830), a radio-loud super-Eddington quasar at z = 3.4351, revealed by Very Long Baseline Array (VLBA) observations at 1.6, 4.9, and 8.2 GHz. Thanks to the high spatial resolution of the VLBA, we successfully resolve a parsec-scale core–jet structure of ID830, and find a well-collimated jet extending over ≈745 pc, making it the most distant and one of the very few currently known radio-loud quasars with a resolved jet associated with super-Eddington accretion. The physical scale and evolutionary track of ID830 differs markedly from the low- z analogues, such as nearby radio-luminous high-Eddington narrow-line Seyfert 1 galaxies, suggesting that this source represents a distinct high- z population compared to previously known samples, with important implications for active galactic nuclei (AGN) feedback in early galaxy evolution. We also find that the jet has a relativistic speed of v ≳ 0.19 c and a modest viewing angle of ϕ ≲ 79° to the line of sight, although its emission is not significantly Doppler-boosted ( δ ∼ 1). This provides the first evidence that such a relativistic and collimated jet can be produced over several hundred parsecs in the super-Eddington phase, lasting for at least 10 3–4 yr. Our results call for further theoretical and numerical studies to understand the physical processes required to sustain such large-scale collimation in super-Eddington accretion, which remains a missing piece.