The Hyperluminous, Dust-obscured Quasar W2246–0526 at z = 4.6: Detection of Parsec-scale Radio Activity

Abstract

Abstract WISE J224607.56−052634.9 (W2246−0526) is a hyperluminous (L bol ≈ 1.7 × 1014 L ⊙), dust-obscured, and radio-quiet quasar at redshift z = 4.6. It plays a key role in probing the transition stage between dusty starbursts and unobscured quasars in the coevolution of galaxies and supermassive black holes (SMBHs). To search for the evidence of the jet activity launched by the SMBH in W2246−0526, we performed very long baseline interferometry observations of its radio counterpart with the European VLBI Network (EVN) plus the enhanced Multi Element Remotely Linked Interferometer Network (e-MERLIN) at 1.66 GHz and the Very Long Baseline Array (VLBA) at 1.44 and 1.66 GHz. The deep EVN plus e-MERLIN observations detect a compact (size ≤ 32 pc) sub-mJy component contributing about 10% of its total flux density, which spatially coincides with the peak of dust continuum and [C II] emissions. Together with its relatively high brightness temperature ( ≥ 8 × 106 K), we interpret the component as a consequence of nonthermal radio activity powered by the central SMBH, which likely originates from a stationary jet base. The resolved-out radio emission possibly come from a diffuse jet, quasar-driven winds, or both, while the contribution by star formation activity is negligible. Moreover, we propose an updated geometry structure of its multiwavelength active nucleus and shed light on the radio quasar selection bias toward the blazars at z > 4.