sciENZO
(shock-injected-cosmic rays in ENZO)


Large Scale Shocks are responsible for the heating of the ICM and can be important sources of Cosmic Rays (CR) in the Universe.
We produced an original implementation to model at run-time the injection, advection and dynamical feedback of CR in
cosmological simulations (also using AMR) working on the public 1.5 release of ENZO.
Read the full article here (Vazza, Bruggen, Gheller & Brunetti 2012 MNRAS)

Tests

We tested our procedure against shock-tubes tests and 1-D zeldovich collapse test, finding very good performances.
Our code allows us to test the various "blocks" of CR physics (i.e. advection, injection, reduced thermalization, pressure feedback)
separately. Also the efficiency of acceleration with M can be varied.



Results

We investigated the distribution of CR in large scale structures, using both fixed grid runs (dx=200kpc/h) and runs with adaptive mesh refinement (dx=25kpc/h).
The most important findings are:

• The level of CR energy inside cosmic structures is found to be small, Pcr/Pg < 0.1, with a peak at the over-density typical of
  outer accretion regions. We report that only the distribution of CRs outside of cosmic structures is strongly dependent on the details
  involved in the acceleration in the early cosmic epochs (and in the  most rarefied environments) while the distributions of CRs are very
  stable for the innermost regions of clusters.
  
• In massive galaxy clusters, the dynamical role of accelerated CR energy is always quite small, and plays a
  significant dynamical role only close to ∼ R200. In the centre of clusters instead the pressure of CRs is small, Pcr/Pg ∼ 0.02 −
  0.05. These values are presently consistent with the upper-limits provided from γ-ray observations.
  
• The effects of CRs on the overall evolution of clusters have small and systematic effects on the 3–D distribution of the thermal
  baryonic gas. In all re-simulated clusters in the innermost gas density, temperature and entropy are reduced by a few percent,
  while they are enhanced on average by the same amount at R200. This comes from the fact that CRs first modify the
  compressibility of outer accretion regions during the formation of structures, leading to an enhanced post-shock compression and to
  a slightly faster expansion of the outer cluster layers compared to standard simulations.
  
• This produces also a corresponding decrease of X-ray emission and of the thermal SZ signal from the inner cluster
  region, and an enhancement of a factor ∼ 0.4−4 close to R200, and depending of the dynamical state of the clusters.
  
•  These systematic trends in galaxy clusters are at variance with SPH simulations, where rather opposite trends are reported.

HERE IS A MOVIE SHOWING THE RUN-TIME INJECTION OF CR, AND THEIR ADVECTION, STARTING FROM Z=1 IN A
COSMOLOGICAL RUN USING AMR (the movie is embedded in Youtube)

slices of Mach number (measured at run-time), injected CR energy flux in the post-shock, and gas energy for a cluster simulated with AMR and our sciENZO modules.

Merger sequence for a cluster simulated with AMR. Top row: gas energy for a slice of 50 kpc/h. Middle row: CR energy within the same slice. Bottom row: ratio of the two for the same regions.