Description
Relativistic jets from active galactic nuclei are expected to exhibit strong redshift evolution in their radiative output due to the increasing energy density of the cosmic microwave background (CMB). In this presentation, we will show how inverse Compton (IC) scattering of CMB photons shapes the radio and X-ray emission from large-scale jets. Our study is based on three-dimensional relativistic magnetohydrodynamic simulations performed with the PLUTO code and coupled to a hybrid Eulerian–Lagrangian particle framework. The simulations incorporate a newly developed IC/CMB radiation module that enables us to quantify the impact of the evolving CMB radiation field on jet emission across cosmic time.
We will show that the simulations reproduce several key observational trends of radio-loud quasars, including the weak redshift dependence of radio luminosity and the pronounced enhancement of X-ray emission toward high redshift. The predicted X-ray luminosity follows the expected $(1+z)^4$ scaling, providing strong support for IC/CMB scattering as the dominant mechanism responsible for the observed X-ray brightening. We will further demonstrate that the X-ray-to-radio flux ratio increases systematically with redshift, consistent with current observational constraints. In addition, slower jets exhibit a stronger redshift evolution of the X-ray enhancement than faster jets, highlighting the important role of jet propagation scales and particle energy evolution in shaping the observed emission. Finally, we will show that the simulations reproduce the observed steepening of the radio spectral index with redshift (the $\alpha$–$z$ relation). Overall, this work provides a unified theoretical framework for interpreting the multiwavelength properties and cosmic evolution of high-redshift radio sources.