Relativistic inverse Compton scattering of photons from the early
  universe
  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.
