Arithmetic with X-ray images of galaxy clusters: effective equation of state for small-scale perturbations in the ICM

TL;DR

This paper introduces a new image manipulation technique for X-ray images of galaxy clusters to classify small-scale perturbations in the intra-cluster medium, revealing their nature and supporting a slow AGN feedback model.

Contribution

The novel image analysis method distinguishes between different perturbation types in galaxy clusters, enhancing understanding of AGN feedback mechanisms.

Findings

Perturbations in M87 and Perseus are mainly isobaric.

Bubbles of relativistic plasma and weak shocks are also significant.

Supports a slow AGN feedback scenario.

Abstract

We discuss a novel technique of manipulating X-ray images of galaxy clusters to reveal the nature of small-scale density/temperature perturbations in the intra cluster medium (ICM). As we show, this technique can be used to differentiate between sound waves and isobaric perturbations in Chandra images of the Perseus and M87/Virgo clusters. The comparison of the manipulated images with the radio data and with the results of detailed spectral analysis shows that this approach successfully classifies the types of perturbations and helps to reveal their nature. For the central regions (5-100 kpc) of the M87 and Perseus clusters this analysis suggests that observed images are dominated by isobaric perturbations, followed by perturbations caused by bubbles of relativistic plasma and weak shocks. Such a hierarchy is best explained in a "slow" AGN feedback scenario, when much of the mechanical energy output of a central black hole is captured by the bubble enthalpy that is gradually released during buoyant rise of the bubbles. The "image arithmetic" works best for prominent structure and for datasets with excellent statistics, visualizing the perturbations with a given effective equation of state. The same approach can be extended to faint perturbations via cross-spectrum analysis of surface brightness fluctuations in X-ray images in different energy bands.