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In an effort to understand the cause of the apparent depletion in the numberdensity of radio-loud AGNs at $z>3$, this work investigates the viability ofthe so-called Cosmic Microwave Background (CMB) quenching mechanism ofintrinsically jetted, high-z AGNs, whereby Inverse Compton scattering of CMBphotons off electrons within the extended lobes results in a substantialdimming of the lobe synchrotron emission at GHz frequencies, whilesimultaneously boosting their diffuse X-ray signal. We focus on five $z>3.5$radio galaxies that have sufficiently deep Chandra exposure (> 50 ks) towarrant a meaningful investigation of any extended X-ray emission. For thoseobjects with evidence for statistically significant extended X-ray lobes (4C41.17 and 4C 03.24), we combine the Chandra measurements with literature dataat lower frequencies to assemble the systems' Spectral Energy Distributions(SEDs), and utilize state-of-the-art SED modelling (Ghisellini et al. 2015) --including emission from the disk, torus, jet, hotspots, and lobes -- to infertheir physical parameters. For both radio galaxies, the magnetic energy densityin the hotspots is found to exceed the energy density in CMB photons, wheresthe opposite is true for the lobes. This implies that any extended synchrotronemission likely originates from the hotspots themselves, rather than the lobes.Conversely, Inverse Compton scattering of CMB photons dominates the extendedX-ray emission from the lobes, which are effectively "radio-quenched". As aresult, CMB quenching is effective in these systems in spite of the fact thatthe observed X-ray to radio luminosity ratio does not bear the signature$(1+z)^4$ dependence of the CMB energy density.

CMB-induced radio quenching of high-redshift jetted AGNs with highly magnetic hotspots