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I will present two related works about high-redshift jetted AGNs in this talk. In the first work, we performed a systematic study of the X-ray and multiwavelength properties of a statistically-meaningful sample of the highly radio-loud quasars (HRLQs; log R > 2.5) at z > 4. In contrast to previous studies on radio-quiet and moderately radio-loud quasars, we found our HRLQs have an X-ray emission enhancement over HRLQs at lower redshifts with similar radio and UV/optical luminosity, and radio loudness values. Our further study with a larger sample confirmed this X-ray emission enhancement. This enhancement can be explained by a fractional IC/CMB mechanism (inverse Compton scattering of the CMB photons) for the jet-linked X-ray emission. In the second work, we studied the viability of the IC/CMB mechanism to quench the radio emission of the high-redshift jetted AGNs, as a possible cause of the apparent depletion in the number density of high-redshift radio-loud AGNs. We focused on z > 3.5 radio galaxies having sufficiently deep Chandra exposure and investigated their extended X-ray emission and the relation to their radio lobes. We utilized the state-of-the-art spectral energy distribution (SED) modeling and found that in the lobes the CMB energy density is higher than that of the magnetic field, which indicates that IC/CMB quenching could be an effective way to dim the radio emission of high-redshift jetted AGNs.
Prof. Jianfeng Wu earned his bachelor (2003) and master (2006) degrees from Tsinghua University. Then he moved to The Pennsylvania State University in USA, obtaining his PhD degree in 2012. He did postdoctoral research afterward at Harvard-Smithsonian Center for Astrophysics and University of Michigan. In 2017 he was selected by the national "Youth Thousand Talents" program and became a professor at Dept. of Astronomy in Xiamen University. His research area covers black holes across the mass scale, studying both physical properties of black holes (e.g., measurement of mass and spin) and their cosmological evolution (e.g., high-redshift quasars). He is specially interested in multiwavelength data analysis and large scale surveys.