Testing the CMB Quenching for High-Redshift Radio Galaxies

The identification of a dozen of high-redshift (z > 4) blazars implies that a much larger population of powerful, but mis-aligned jetted AGNs already exists in the early Universe. However, this parent population remains elusive, although they are expected to be within the sensitivity threshold of modern wide-field radio surveys. One appealing mechanism is that the CMB photons upscatter the diffuse synchrotron radio emission in the lobes to the X-ray band. In this scenario, the lobes will turn into luminous X-ray sources. We analyzed the extended X-ray emission around several radio galaxies at z~4 and constructed their broad-band spectral energy distributions (SEDs). Modeling their SEDs will test this CMB quenching scenario for high-redshift radio galaxies.