On the Nature of X-ray Surface Brightness Fluctuations in M87

TL;DR

This study analyzes X-ray surface brightness fluctuations in M87 to identify dominant physical processes like shocks, bubbles, or cold gas uplift, using simulations and multi-band analysis to distinguish these phenomena.

Contribution

It provides a detailed characterization of the nature of X-ray fluctuations in M87, confirming the dominance of specific processes and extending understanding of AGN feedback mechanisms.

Findings

Cool filaments are isobaric and in pressure equilibrium with hot gas.

Weak shocks exhibit adiabatic behavior at specific radii.

Central region shows a mix of isothermal and adiabatic fluctuations.

Abstract

X-ray images of galaxy clusters and gas-rich elliptical galaxies show a wealth of small-scale features which reflect fluctuations in density and/or temperature of the intra-cluster medium. In this paper we study these fluctuations in M87/Virgo, to establish whether sound waves/shocks, bubbles or uplifted cold gas dominate the structure. We exploit the strong dependence of the emissivity on density and temperature in different energy bands to distinguish between these processes. Using simulations we demonstrate that our analysis recovers the leading type of fluctuation even in the presence of projection effects and temperature gradients. We confirm the isobaric nature of cool filaments of gas entrained by buoyantly rising bubbles, extending to 7' to the east and south-west, and the adiabatic nature of the weak shocks at 40" and 3' from the center. For features of 5--10 kpc, we show that the central 4'x 4' region is dominated by cool structures in pressure equilibrium with the ambient hotter gas while up to 30 percent of the variance in this region can be ascribed to adiabatic fluctuations. The remaining part of the central 14'x14' region, excluding the arms and shocks described above, is dominated by apparently isothermal fluctuations (bubbles) with a possible admixture (at the level of about 30 percent) of adiabatic (sound waves) and by isobaric structures. Larger features, of about 30 kpc, show a stronger contribution from isobaric fluctuations. The results broadly agree with an AGN feedback model mediated by bubbles of relativistic plasma.