The generation of optical emission-line filaments in galaxy clusters

TL;DR

This paper uses numerical simulations to explore how high-velocity winds interacting with evaporating gas clouds can produce the optical filaments observed in galaxy clusters, suggesting a role in energy dissipation and feedback.

Contribution

It demonstrates that fast outflows can create filamentary structures similar to observations and highlights their potential role in cluster energy regulation.

Findings

Filaments form only with wind velocities above 10^8 cm/s.

Simulated filament morphology matches observed structures.

Filament ages are estimated to be a few tens of Myrs.

Abstract

Recent data support the idea that the filaments observed in H_alpha emission near the centres of some galaxy clusters were shaped by bulk flows within their intracluster media. We present numerical simulations of evaporated clump material interacting with impinging winds to investigate this possibility. In each simulation, a clump falls due to gravity while the drag of a wind retards the fall of evaporated material leading to elongation of the tail. However, we find that long filaments can only form if the outflowing wind velocity is sufficiently large, 10^8 cm s^-1. Otherwise, the tail material sinks almost as quickly as the cloud. For reasonable values of parameters, the morphological structure of a tail is qualitatively similar to those observed in clusters. Under certain conditions, the kinematics of the tail resemble those reported in Hatch et al.(2006). A comparison of the observations with the numerical results indicates that the filaments are likely to be a few tens of Myrs old. We also present arguments which suggest that the momentum transfer, from an outflowing wind, in the formation of these filaments is probably significant. As a result, tail formation could play a role in dissipating some of the energy injected by a central AGN close to the cluster centre where it is needed most. The trapping of energy by the cold gas may provide an additional feedback mechanism that helps to regulate the heating of the central regions of galaxy clusters and couple the AGN to the ICM.