Jet Physics of MG3 J163554+3629 and Its Impact on Supermassive Black Hole Evolution in the Early Universe

The origin and growth of supermassive black holes (SMBHs) in the early universe, particularly in the first billion years after the Big Bang, remains one of the most intriguing challenges in astrophysics. Detecting active galactic nuclei (AGN) in this era is hindered by their faint emissions due to the vast distances involved. However, blazars, a unique subclass of AGN with relativistic jets pointed directly towards Earth, provide an exceptional opportunity to study SMBH evolution at high redshifts. In this thesis we model the broadband spectral energy distribution (SED) of MG3 J163554+36291 at z = 3.65, one of the highest-redshift blazars detected by the Fermi Large Area Telescope. The model includes recent NuSTAR hard X-ray data and is built with a one-zone leptonic model in JetSeT, for accretion efficiencies η = 0.057–0.3, corresponding to black hole spins from a = 0 to nearly maximal. We find a black hole mass MBH ≃ 1.8 × 109 M⊙ and an Eddington ratio λ ≃ 0.08 for an inner disk radius of 8 RS . The NuSTAR band is produced by a mix of synchrotron self-Compton and external Compton emission, and the γ-rays by Compton scattering of torus photons. The jet is particle-dominated and carries more power than the disk radiates. If the black hole had always accreted at its present Eddington ratio, the seed at z = 30 would need to be ≳ 107 M⊙ , above the most massive direct-collapse seeds. The black hole must therefore have grown through an earlier phase of faster accretion, with a radiative efficiency well below the value for a maximally spinning black hole.