Extended X-Ray Emission Associated with the Radio Lobes and the Environments of 60 Radio Galaxies

This paper studied the faint, diffuse extended X-ray emission associated with the radio lobes and the hot gas in the intracluster medium (ICM) environment for a sample of radio galaxies. We used shallow (similar to 10 ks) archival Chandra observations for 60 radio galaxies (7 FR I and 53 FR II) with 0.0222 <= z <= 1.785 selected from the 298 extragalactic radio sources identified in the 3CR catalog. We used Bayesian statistics to look for any asymmetry in the extended X-ray emission between regions that contain the radio lobes and regions that contain the hot gas in the ICM. In the Chandra broad band (0.5-7.0 keV), which has the highest detected X-ray flux and the highest signal-to-noise ratio, we found that the nonthermal X-ray emission from the radio lobes dominates the thermal X-ray emission from the environment for similar to 77% of the sources in our sample. We also found that the relative amount of on-jet axis nonthermal emission from the radio lobes tends to increase with redshift compared to the off-jet axis thermal emission from the environment. This suggests that the dominant X-ray mechanism for the nonthermal X-ray emission in the radio lobes is due to the inverse Compton upscattering of cosmic microwave background (CMB) seed photons by relativistic electrons in the radio lobes, a process for which the observed flux is roughly redshift independent due to the increasing CMB energy density with increasing redshift.