# Relativistic inverse Compton scattering of photons from the early universe

## TL;DR

This paper reports the first clear detection of non-thermal electron pressure in a radio galaxy jet/lobe, which helps constrain the low-energy cutoff of electron energies critical for understanding cosmic structure formation.

## Contribution

It introduces a novel measurement of non-thermal electron pressure in a radio galaxy, providing insights into electron energy distributions in galaxy clusters.

## Key findings

- Detected non-thermal electron pressure in a radio galaxy jet/lobe
- Constrained the low-energy cutoff of electron energies (pmin)
- Implications for understanding large-scale structure formation

## Abstract

Electrons at relativistic speeds, diffusing in magnetic fields, cause copious emission at radio frequencies in both clusters of galaxies and radio galaxies, through the non-thermal radiation emission called synchrotron. However, the total power radiated through this mechanism is ill constrained, as the lower limit of the electron energy distribution, or low-energy cutoffs, for radio emission in galaxy clusters and radio galaxies have not yet been determined. This lower limit, parametrized by the lower limit of the electron momentum - pmin - is critical for estimating the energetics of non-thermal electrons produced by cluster mergers or injected by radio galaxy jets, which impacts the formation of large-scale structure in the universe, as well as the evolution of local structures inside galaxy clusters. The total pressure due to the relativistic, non-thermal population of electrons is critically dependent on pmin, making the measurement of this non-thermal pressure a promising technique to estimate the electron low-energy cutoff. We present here the first unambiguous detection of this pressure for a non-thermal population of electrons in a radio galaxy jet/lobe, located at a significant distance away from the center of the Bullet cluster of galaxies.