Analytical Models
of Cosmic Accretion Shocks
and the Role of Environment

Cosmic accretion shocks are found at the interface between a collapsed cosmic structure (e.g., a cluster of galaxies) and its surrounding diffuse intergalactic gas. They are like bullies in the schoolyard: they are big, they are strong and they can make the little guys run at the speed of light.

After its formation through gravitational collapse, a cosmic structure coninues to accumulate matter from its surroundings. Cosmic accretion shocks are formed where the infalling, accelerated gas meets the gaseous content of the collapsed structures. Such shocks process the enormous amount of kinetic energy present in the accreting gas, and convert part of it to heat, and part of it to kinetic energy of relativistic particles, aka "cosmological cosmic rays". The properties of each shock depend on the properties of the accretor as well as the physical conditions in its immediate environment.

We used the Double Distribution of dark mater halos, which describes the statistical properties of both the accretors and their environment, to construct analytical models for the statistical properties of the population of accretion shocks. We examined how environmental factors affect the properties of accretion shocks, and evaluated the physical impact of accretion shocks on their environment, i.e. the intergalactic gas. We found that (1) environmental effects are essential in determining the properties of cosmic accretion shocks, and the effect of both local clustering and cosmic filaments have to be accounted for in order to correctly predict the effect of accretion shocks on the intergalactic medium; (2) for all redshifts smaller than ~3, cosmic accretion shocks process more energy than the collective output of all supernova explosions in a comparable volume and over comparable time intervals - in fact, at the present cosmic epoch, the energy processed by cosmic accretion shocks overtakes the energy released by supernovae by more than an oredr of magnitude.

Reference: Pavlidou, V., & Fields, B. D. 2006, ApJ, 642, 734
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