On the X-ray emission of z radio galaxies: IC scattering of the CMB and no evidence for fully-formed potential wells

¹ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: overzier@strw.leidenuniv.nl
² Smithsonian Astronomical Observatory, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ National Radio Astronomy Observatory, New Mexico Array Operations Center (VLA, VLBA), PO Box O, 1003 Lopezville Road, Socorro, NM 87801, USA
⁴ Dipartimento di Fisica, Università degli Studi Roma Tre, Rome, Italy

Received: 13 July 2004
Accepted: 30 November 2004

Abstract

We present the results of 20 ks Chandra observations for each of 5 radio galaxies in the redshift range . The goals were to (i) study the nature of their non-thermal X-ray emission; (ii) investigate the presence and amount of hot gas; and (iii) look for active galactic nuclei (AGN) overdensities in fields around high redshift radio galaxies. For 4 of the 5 targets we detect unresolved X-ray components coincident with the radio nuclei. From spectral analysis of one of the cores and comparison to the empirical radio to X-ray luminosity ratio () correlation for AGN, we find that the cores are underluminous in the X-rays indicating that obscuring material ( cm^-2) may be surrounding the nuclei. 
We detect X-ray emission coincident with the radio hotspots or lobes in 4 of the 5 targets. This extended emission can be explained by the Inverse-Compton (IC) scattering of photons that make up the cosmic microwave background (CMB). The magnetic field strengths of  μG that we derive agree with the equipartition magnetic field strengths. The relative ease with which the lobe X-ray emission is detected is a consequence of the increase in the energy density of the CMB. For one of the lobes, the X-ray emission could also be produced by a reservoir of hot, shocked gas. An HST image of the region around this radio component shows bright optical emission reminiscent of a bow-shock.
By co-adding the 5 fields we created a deep, 100 ks exposure to search for diffuse X-ray emission from thermal intra-cluster gas. We detect no diffuse emission and derive upper limits of  erg s^-1, thereby ruling out a virialized structure of cluster-size scale at . 
The average number of soft X-ray sources in the field surrounding the radio sources is consistent with the number density of AGN in the Chandra Deep Fields, with only one of the fields showing a marginally statistically significant factor 2 excess of sources with  erg s^-1 cm^-2. Analysis of the angular distribution of the field sources shows no evidence for large-scale structure associated with the radio galaxies, as was observed in the case of PKS 1138-262 by [CITE].