Formation of cold filaments in cooling flow clusters

TL;DR

This paper uses high-resolution simulations to study how AGN activity in galaxy clusters leads to the formation of cold filamentary structures through gas cooling and entrainment by buoyant bubbles.

Contribution

It introduces a detailed simulation model combining multiphase gas dynamics and plasma bubbles to explain filament formation in cooling flow clusters.

Findings

Cold filaments form in the wake of rising bubbles due to radiative cooling.

A fraction of hot gas is entrained and cooled to form filaments.

Simulations match observed filament structures in clusters like Perseus.

Abstract

Emission-lines in the form of filamentary structures is common in bright clusters characterized by short cooling times. In the Perseus cluster, cold molecular gas, tightly linked to the H$\alpha$ filaments, has been recently revealed by CO observations. In order to understand the origin of these filamentary structures, we have investigated the evolution of the hot ICM gas perturbed by the AGN central activity in a Perseus like cluster. Using very-high resolution TreeSPH simulations combined with a multiphase model and a model of plasma bubbles, we have been able to follow the density and temperature evolution of the disturbed ICM gas around the bubbles. Our simulations show that a fraction of the $1-2 \rm{keV}$ gas present at the center of clusters is trapped and entrained by the rising buoyant bubble to higher radius where the AGN heating is less efficient. The radiative cooling makes it cool in a few tens of Myr below $10^4 \rm{K}$, forming cold filamentary structures in the wake and in the rim of the bubbles.