Hidden Cooling Flows in Clusters of Galaxies

TL;DR

This study investigates hidden cooling flows in galaxy clusters, revealing significant amounts of cooled gas that are obscured in X-ray observations but detectable in the far infrared, challenging current understanding of cluster cooling.

Contribution

Introduces an intrinsic absorption model to uncover hidden cooling flows in galaxy clusters, linking X-ray and far infrared observations to estimate unseen cooled gas.

Findings

Hidden cooling rates range from 10 to 500 Msunpyr.

Far infrared emission accounts for the absorbed cooling emission.

Total cooled gas mass exceeds observed molecular gas masses.

Abstract

The radiative cooling time of the hot gas at the centres of cool cores in clusters of galaxies drops down to 10 million years and below. The observed mass cooling rate of such gas is very low, suggesting that AGN feedback is very tightly balanced or that the soft X-ray emission from cooling is somehow hidden from view. We use an intrinsic absorption model in which the cooling and coolest gas are closely interleaved to search for hidden cooling flows in the Centaurus, Perseus and A1835 clusters of galaxies. We find hidden mass cooling rates of between 10 to 500 Msunpyr as the cluster mass increases, with the absorbed emission emerging in the Far Infrared band. Good agreement is found between the hidden cooling rate and observed FIR luminosity in the Centaurus Cluster. The limits on the other two clusters allow for considerable hidden cooling. The implied total mass of cooled gas is much larger than the observed molecular masses. We discuss its fate including possible further cooling and collapse into undetected very cold clouds, low mass stars and substellar objects,