Cosmological Simulations of Isotropic Conduction in Galaxy Clusters

TL;DR

This study uses cosmological simulations to test isotropic thermal conduction's effects on galaxy cluster properties, finding limited impact on observable features and questioning its detectability in typical clusters.

Contribution

First systematic exploration of isotropic Spitzer conduction effects in cosmological galaxy cluster simulations, assessing its influence on cluster core and outskirts.

Findings

Conduction flattens core temperature gradients but doesn't prevent cooling catastrophe.

Little effect of conduction on temperature gradients outside cores.

Conduction reduces gas densities and temperatures outside the virial radius.

Abstract

Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of ten galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, but not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the intracluster medium (ICM) instead of raising its temperature. In general, conduction tends reduce temperature inhomogeneity in the ICM, but our simulations indicate that those homogenizing effects would be extremely difficult to observe in ~5 keV clusters. Outside the virial radius, our conduction implementation lowers the gas densities and temperatures because it reduces the Mach numbers of accretion shocks. We conclude that despite the numerous small ways in which conduction alters the structure of galaxy clusters, none of these effects are significant enough to make the efficiency of conduction easily measurable unless its effects are more pronounced in clusters hotter than those we have simulated.