Cooling Flows in Clusters and Galaxies

X-ray astronomers discovered the diffuse gas in clusters of galaxies about 20 years ago. It was later realized that the central gas density in some clusters, and in elliptical galaxies, is so high that radiative cooling is a significant energy loss. The cooling time of the gas decreases rapidly towards the centre of the cluster or galaxy and is less than a Hubble time within the innermost few hundred kiloparsecs. This results in a cooling flow in which the gas density rises in order to maintain pressure to support the weight of the overlying gas. The rate at which mass is deposited by the flow is inferred to be several hundreds of solar masses per year in some clusters. The fraction of clusters in which cooling flows are found may exceed 50 per cent. Small flows probably occur in most normal elliptical galaxies that are not in rich clusters. The implications of this simple phenomenon are profound, for we appear to be witnessing the ongoing formation of the central galaxy. In particular, since most of the gas is undetected once it cools below about 3 million K, it appears to form dark matter. There is no reason why it should be detectable with current techniques if each cooling proton only recombines once and the matter condenses into objects of low mass.

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Properties of Clusters of Galaxies.- Clusters of Galaxies and Cooling Hot Gas.- A Catalog(UE) of Cooling Flows.- Alternative Cooling Flow Models.- The Role of Heat Conduction in Cooling Flows.- Einstein Observatory Solid State Detector Observations of Cooling Flows in Clusters of Galaxies.- X-Ray Emission Lines from Cooling Flows.- Optical, Ultraviolet, and Infrared Observations of Cooling Flows in Rich Clusters.- Dynamics of Cosmic Rays in Cooling Flows.- Hot and Cold Gas in Early-Type Galaxies: A Comparison of X-Ray, HI and Far Infrared Emission.- Evidence for Star Formation in Cooling Flows.- Dynamical Friction in the Rich Cluster A2029.- Color Gradients in Cooling Flow Cluster Central Galaxies and the Ionization of Cluster Emission Line Systems.- Ultraviolet Evidence for Star Formation in Elliptical Galaxies.- Characteristics of Extended Gas Around Radio Galaxies.- HI Absorption Detection in the Perseus Cooling Flow.- Radio Observations of NGC 1275 at 90 and 20 cm.- Photoionization Versus Shocks in the Filaments of NGC 1275.- Cooling Flow Filaments and the Emission-Line Gas in NGC 1275.- Exosat Data on Clusters.- Thermal Instability in Cooling Flows.- Radio Emission in Cooling Flows.- Emission from Thermal Instabilities.- Radio Sources and Cooling Flows.- The Depolarization of Radio Sources by Cluster Gas.- The Structure of Elliptical Galaxies.- Dynamics of E Galaxies and Cluster Sources.- Cooling Flows in Galaxies.- Detailed Spectroscopic Investigation of Emission-Line Nebulae Associated with Cooling Flows.- Jet-Induced Starbursts: from Minkowski's Object to Distant Radio Galaxies.- Radio Jets as a Probe of the Cooling Flow Environment.- Optical Emission Lines in Early-Type Galaxies.- Radio and X-Ray Emission in Early-Type Galaxies.- Ecology and Evolution of Ellipticals.- Warm Gas in Radio Galaxies.- Hell 4686/h/? as a Constraint on the Ionizing Continuum.- Photoionization of Extended Emission Line Regions.- The Evolution of Early-Type Galaxies.- Some Implications of Distant Cooling Flows.- Extended Emission-Line Gas in Distant 3CR Radio Galaxies.- Cooling Flows around Quasars.- A Semi-Analytic Approach to Cooling Flow Evolution.- The Current Evolution of X-Ray Cluster Cooling Flows.- Non-Steady Considerations for Cooling Flows.- Cosmology and Cooling Flows.- Multiphase Cooling Flows and Galaxy Formation.- The Role of Magnetic Fields in Cluster Cooling Flows.- HI in Cooling Flow Ellipticals.- Discussion Papers.- Object Index.