Virial shocks in galaxy clusters


  Kuan-Chou Hou  ,  Uri Keshet  ,  Gideon Ilani  ,  Ido Reiss  
Physics Department, Ben-Gurion University of the Negev
Physics Department, Nuclear Research Center Negev

In the theory of structure formation in the Universe, galaxy clusters are thought to grow by accreting surrounding material, resulting in strong, so-called virial, shocks. Such a shock is expected to accelerate relativistic electrons, thus generating a spectrally-flat leptonic virial ring. A significant (5.8σ) virial shock signal was identified near the expected shock radius, $\sim 2.5R_{500}$, by stacking gamma-ray data from Fermi LAT around 112 nearby clusters. We provide new virial shock signals over a wide range of wavelengths, better localizing the phenomenon and measuring the shock properties. Understanding these shocks has implications for astrophysics, cosmology, and plasma physics; in particular, we estimate the energies that the shock deposits in relativistic electrons and magnetic fields.