Unveiling the origin of filament formation in cooling flow clusters

Joint X-ray and radio observations of central cluster galaxies have shown that AGN radio jets can push the hot gas and form cavities in the intracluster medium (ICM), providing clear evidence of AGN feedback. Local BCGs hosting multiphase filamentary structures have been detected in numerous cooling flow clusters, where filaments are an outcome of thermally unstable cooling from the hot ICM likely triggered by AGN feedback. The details, however, behind the formation mechanism of these striking filaments are still debatable.

Inspired by the Halpha to X-ray relation found for diffuse gas in stripped tails, we explored the local properties of the X-ray and optical emitting filaments in cooling flow clusters using in synergy Chandra and MUSE observations. For the first time, we isolated the X-ray filaments, which are blended in the diffuse ICM, using a novel method of imagining decomposition. By comparing the hot and ionized phase of the filaments, we discover a linear correlation between the X-ray and the Halpha surface brightness of extended 10 — 50 kpc scales filaments in cooling flow clusters. We also explore various properties of the X-ray filaments, and investigate if the ionized and hot phases of the filaments are in pressure equilibrium; our findings provide strong evidence that the condensation of the cold filaments depends on the local properties of the hot ICM.