Discovery of a Kiloparsec Scale X-ray/Radio Jet in the z=4.72 Quasar GB 1428+4217

TL;DR

This paper reports the discovery of the highest-redshift kiloparsec-scale X-ray/radio jet in a quasar at z=4.72, providing insights into jet properties and inverse Compton processes at early cosmic times.

Contribution

First detection of a kiloparsec-scale X-ray/radio jet at such a high redshift, expanding understanding of jet evolution and inverse Compton scattering in the early universe.

Findings

Highest-redshift kiloparsec-scale X-ray/radio jet known.

Jet Lorentz factor estimated at ~5, lower than in lower-redshift jets.

High-redshift jets may be less relativistic on large scales.

Abstract

We report the discovery of a one-sided 3.6" (24 kpc, projected) long jet in the high-redshift, z=4.72, quasar GB 1428+4217 in new Chandra X-ray and VLA radio observations. This is the highest redshift kiloparsec-scale X-ray/radio jet known. Analysis of archival VLBI 2.3 and 8.6 GHz data reveal a faint one-sided jet extending out to ~200 parsecs and aligned to within ~30 deg of the Chandra/VLA emission. The 3.6" distant knot is not detected in an archival HST image, and its broad-band spectral energy distribution is consistent with an origin from inverse Compton scattering of cosmic microwave background photons for the X-rays. Assuming also equipartition between the radiating particles and magnetic field, the implied jet Lorentz factor is ~5. This is similar to the other two known z ~ 4 kpc-scale X-ray jet cases and smaller than typically inferred in lower-redshift cases. Although there are still but a few such very high-redshift quasar X-ray jets known, for an inverse Compton origin, the present data suggest that they are less relativistic on large-scales than their lower-redshift counterparts.