X-ray emission around the z=4.1 radio galaxy TNJ1338-1942 and the potential role of far-infrared photons in AGN Feedback

TL;DR

This study reports the first detection of extended X-ray emission around a high-redshift radio galaxy, suggesting far-infrared photons from starbursts may significantly contribute to AGN feedback via inverse Compton scattering.

Contribution

It introduces the idea that far-infrared photons, rather than the CMB, dominate seed photons for inverse Compton emission in early radio-loud AGN.

Findings

Detected extended X-ray emission at z=4.11 around TNJ1388-1942.

Found a tentative correlation between IC emission and far-infrared luminosity.

Proposed far-infrared photons contribute to AGN feedback at high redshift.

Abstract

We report the discovery in an 80-ks observation of spatially-extended X-ray emission around the high-redshift radio galaxy TNJ1388-1942 (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 ~700x 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 <100kpc). Based on these results we suggest that in the earliest phases of the evolution of radio-loud AGN at very high redshift, the far-infrared photons from the co-eval dusty starbursts occuring 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.