Evolution of X-ray cavities

TL;DR

This study uses simulations and synthetic observations to analyze the morphological evolution of X-ray cavities in galaxy clusters, revealing anisotropic size changes and emphasizing the need for detailed modeling to interpret observations accurately.

Contribution

It combines numerical simulations with synthetic X-ray observations to investigate cavity evolution without magnetic fields, highlighting differences from analytical models and key factors affecting interpretation.

Findings

Cavity size evolution is anisotropic and differs from simplified models.

Inferred pV energy correlates with distance from cluster center.

Current models cannot distinguish hydrodynamic from magnetic dominance.

Abstract

A wide range of recent observations have shown that AGN-driven cavities may provide the energy source that balances the cooling observed in the centres of cool-core galaxy clusters. One tool for better understanding the physics of these cavities is their observed morphological evolution, which is dependent on such poorly-understood properties as the turbulent density field and the impact of magnetic fields. Here we combine numerical simulations that include subgrid turbulence and software that produces synthetic X-ray observations to examine the evolution of X-ray cavities in the absence of magnetic fields. Our results reveal an anisotropic size evolution of that is dramatically different from simplified, analytical predictions. These differences highlight some of the key issues that must be accurately quantified when studying AGN-driven cavities, and help to explain why the inferred pV energy in these regions appears to be correlated with their distance from the cluster center. Interpreting X- ray observations will require detailed modeling of effects including mass-entrainment, distortion by drag forces, and pro jection. Current limitations do not allow a discrimination between purely hydrodynamic and magnetically-dominated models for X-ray cavities.