Direct observation of an extended X-ray jet at z = 6.1

¹ INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
² DiSAT – Università degli Studi dell’Insubria, via Valleggio 11, 22100 Como, Italy
e-mail: lighina@uninsubria.it
³ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
⁴ Department of Physics and Astronomy, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁵ INAF – Institute for Radioastronomy, via Gobetti 101, 40129 Bologna, Italy

Received: 16 November 2021
Accepted: 12 January 2022

Abstract

We report on the direct observation of an extended X-ray jet in the z = 6.1 radio-loud active galactic nucleus PSO J030947.49+271757.31 from a deep Chandra X-ray observation (128 ksec). This detection represents the most distant kiloparsec-scale off-nuclear emission resolved in X-rays to date. The angular distance of the emission is ∼4″ (corresponding to ∼20 kpc at z = 6.1), along the same direction of the jet observed at parsec scales in previous VLBA high-resolution radio observations. Moreover, the 0.5–7.0 keV isophotes coincide with the extended radio emission as imaged by the VLA Sky Survey at 3 GHz. The rest-frame 2–10 keV luminosity of the extended component is L_2 − 10 keV = 5.9 × 10⁴⁴ erg s⁻¹, about 8% of the core: this makes it one of the most luminous jets resolved in X-rays so far. Through spectral energy distribution modelling we find that this emission can be explained by the inverse Compton interaction with the photons of the cosmic microwave background, assuming that the jet’s physical parameters are similar to those in the local Universe. At the same time, we find that the radiation produced by a putative population of high-energy electrons through the synchrotron process observed at low redshift is quenched at high redshift, hence becoming negligible.