X-ray emission around the z = 4.1 radio galaxy TN J1338-1942 and the potential role of far-infrared photons in AGN feedback.

We report the discovery in an 80-ks observation of spatially extended X-ray emission around the high-redshift radio galaxy TN J1388−1942 (z = 4.11) with the Chandra X-ray Observatory. The X-ray emission extends over a ∼30-kpc diameter region and although it is less extended than the GHz-radio lobes, it is roughly aligned with them. We suggest that the X-ray emission arises from inverse-Compton (IC) scattering of photons by relativistic electrons around the radio galaxy. At z = 4.11, this is the highest redshift detection of IC emission around a radio galaxy. We investigate the hypothesis that in this compact source, the cosmic microwave background (CMB), which is ∼700× more intense than at z ∼ 0 is nonetheless not the relevant seed photon field for the bulk of the IC emission. Instead, we find a tentative correlation between the IC emission and far-infrared luminosities of compact, far-infrared luminous high-redshift radio galaxies (those with lobe lengths of ≲100 kpc). Based on these results, we suggest that in the earliest phases of the evolution of radio-loud active galactic nuclei at very high redshift, the far-infrared photons from the co-eval dusty starbursts occurring within these systems may make a significant contribution to their IC X-ray emission and so contribute to the feedback in these massive high-redshift galaxies