Annu. Rev. Astron. Astrophys. 2003. 41: 191-239 Copyright © 2003 by Annual Reviews. All rights reserved

Reprinted with kind permission from Annual Reviews, 4139 El Camino Way, Palo Alto, California, USA

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Abstract. We review the origin, evolution and physical nature of hot gas in elliptical galaxies and associated galaxy groups. Unanticipated recent X-ray observations with Chandra and XMM indicate much less cooling than previously expected. Consequently, many long-held assumptions need to be reexamined or discarded and new approaches must be explored. Chief among these are the role of heating by active galactic nuclei, the influence of radio lobes on the hot gas, details of the cooling process, possible relation between the hot and colder gas in elliptical galaxies, and the complexities of stellar enrichment of the hot gas.

Keywords elliptical galaxies, X-rays, cooling flows, galaxy groups, galaxy clusters

Table of Contents

• INTRODUCTION
• OVERVIEW OF HOT GAS FLOWS IN AND NEAR ELLIPTICAL GALAXIES
• BASIC PROPERTIES OF ELLIPTICAL GALAXIES AND THEIR HOT GAS
• HYDROSTATIC EQUILIBRIUM AND MASS DETERMINATIONS
• GAS DYNAMICAL EQUATIONS AND CLASSIC COOLING FLOWS
• SIMPLE COOLING FLOW MODELS
• THE COOLING PARADOX - DOES THE GAS COOL?
• Spectroscopic and Morphological Cooling Rates
• Warm and Cold Gas at T < 10⁵ K
• Dust in Elliptical Galaxies
• Origin of Warm Gas, Cold Gas and Dust
• Hiding the Cooling Gas
• COOLING FLOWS HEATED BY ACTIVE NUCLEI
• Chandra Observations and Entropy Floors
• AGN Heating
• Cooling Flow Models with Heating
• Models of X-ray Cavities
• ROTATION AND MAGNETIC FIELDS
• ABUNDANCES IN THE HOT GAS
• REFERENCES