Discovery of a kiloparsec-scale X-ray/radio jet in the z = 4.72 quasar GB 1428+4217

Abstract

We report the discovery of a one-sided 36 (24kpc, projected) long jet in the high-redshift, z = 4.72, quasar GB1428+4217 in new Chandra X-ray and Very Large Array (VLA) radio observations. This is the highest redshift kiloparsec-scale X-ray/radio jet known. Analysis of archival very long baseline interferometry 2.3 and 8.6GHz data reveal a faint one-sided jet extending out to ∼200pc and aligned to within ∼30° of the Chandra/VLA emission. The 36 distant knot is not detected in an archival Hubble Space Telescope image, and its broadband 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 ∼ 4kpc 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. © © 2012. The American Astronomical Society. All rights reserved.