Shock finding on a moving-mesh: II. Hydrodynamic shocks in the Illustris universe

TL;DR

This paper analyzes hydrodynamic shocks in the Illustris cosmological simulation, revealing the impact of complex physics on shock properties, morphology, and energy dissipation, with implications for galaxy formation and feedback processes.

Contribution

The study introduces improved shock finding methods for simulations with detailed physics and compares shock characteristics between radiative and non-radiative runs, highlighting the effects of feedback.

Findings

Shock surface area is 1.4 times larger in Illustris than non-radiative runs.

Energy dissipation at shocks is about 7 times higher in Illustris.

Shocks with Mach numbers above and below 10 contribute equally to dissipation.

Abstract

Hydrodynamical shocks are a manifestation of the non-linearity of the Euler equations and play a fundamental role in cosmological gas dynamics. In this work, we identify and analyse shocks in the Illustris simulation, and contrast the results with those of non-radiative runs. We show that simulations with more comprehensive physical models of galaxy formation pose new challenges for shock finding algorithms due to radiative cooling and star-forming processes, prompting us to develop a number of methodology improvements. We find in Illustris a total shock surface area which is about 1.4 times larger at the present epoch compared to non-radiative runs, and an energy dissipation rate at shocks which is higher by a factor of around 7. Remarkably, shocks with Mach numbers above and below $\mathcal{M}\approx10$ contribute about equally to the total dissipation across cosmic time. This is in sharp contrast to non-radiative simulations, and we demonstrate that a large part of the difference arises due to strong black hole radio-mode feedback in Illustris. We also provide an overview of the large diversity of shock morphologies, which includes complex networks of halo-internal shocks, shocks on to cosmic sheets, feedback shocks due to black holes and galactic winds, as well as ubiquitous accretion shocks. In high redshift systems more massive than $10^{12}\,\mathrm{M}_\odot$ we discover the existence of a double accretion shock pattern in haloes. They are created when gas streams along filaments without being shocked at the outer accretion shock, but then forms a second, roughly spherical accretion shock further inside.