A radio structure resolved at the deca-parsec scale in radio-quiet quasar PDS 456 with an extremely powerful X-ray outflow

TL;DR

This study uses VLBI observations to resolve a radio structure at deca-parsec scales in the radio-quiet quasar PDS 456, revealing potential jet or outflow features associated with powerful X-ray driven winds near the supermassive black hole.

Contribution

First high-resolution VLBI imaging of PDS 456 revealing deca-parsec scale radio structures linked to AGN outflows and jets in a radio-quiet quasar.

Findings

Detection of two faint radio components separated by ~20 pc.

Identification of possible young jet or bidirectional outflow.

Tentative detection of relic radio emission at hecto-pc scales.

Abstract

Active galactic nuclei (AGN) accreting at rates close to the Eddington limit can host radiatively driven mildly relativistic outflows. Some of these X-ray absorbing but powerful outflows may produce strong shocks resulting in a significant non-thermal emission. This outflow-driven radio emission may be detectable in the radio-quiet quasar PDS 456 since it has a bolometric luminosity reaching the Eddington limit and a relativistic wide-aperture X-ray outflow with a kinetic power high enough to quench the star formation in its host galaxy. To investigate this possibility, we performed very-long-baseline interferometric (VLBI) observations of the quasar with the European VLBI Network (EVN) at 5 GHz. The EVN image with the full resolution reveals two faint and diffuse radio components with a projected separation of about 20 pc and an average brightness temperature of around two million Kelvin. In relation to the optical sub-mas-accuracy position measured by the Gaia mission, the two components are very likely on opposite sides of an undetected radio core. The VLBI structure at the deca-pc scale can thus be either a young jet or a bidirectional radio-emitting outflow, launched in the vicinity of a strongly accreting central engine. Two diffuse components at the hecto-pc scale, likely the relic radio emission from the past AGN activity, are tentatively detected on each side in the low-resolution EVN image.