Starburst and post-starburst high-redshift protogalaxies: The feedback
  impact of high energy cosmic rays
  Quenching of star-formation has been identified in many starburst and
post-starburst galaxies, indicating burst-like star-formation histories (SFH)
in the primordial Universe. We have investigated the role of high energy cosmic
rays (CRs) in such environments, particularly how they could contribute to this
burst-like SFH via quenching and feedback. These high energy particles interact
with the baryon and radiation fields of their host via hadronic processes to
produce secondary leptons. The secondary particles then also interact with
ambient radiation fields to generate X-rays through inverse-Compton scattering.
In addition, they can thermalise directly with the semi-ionised medium via
Coulomb processes. Heating at a rate of $\sim 10^{-25} \;
\text{erg}~\text{cm}^{-3}~\text{s}^{-1}$ can be attained by Coulomb processes
in a star-forming galaxy with one core-collapse SN event per decade, and this
is sufficient to cause quenching of star-formation. At high-redshift, a
substantial amount of CR secondary electron energy can be diverted into
inverse-Compton X-ray emission. This yields an X-ray luminosity of above
$10^{41}~\text{erg}~\text{s}^{-1}$ by redshift $z=7$ which drives a further
heating effect, operating over larger scales. This would be able to halt
inflowing cold gas filaments, strangulating subsequent star-formation. We
selected a sample of 16 starburst and post-starburst galaxies at $7\lesssim z
\lesssim 9$ and determine the star-formation rates they could have sustained.
We applied a model with CR injection, propagation and heating to calculate
energy deposition rates in these 16 sources. Our calculations show that CR
feedback cannot be neglected as it has the strength to suppress star-formation
in these systems. We also show that their currently observed quiescence is
consistent with the suffocation of cold inflows, probably by a combination of
X-ray and CR heating.
