Feedback and Environmental Effects in Elliptical Galaxies
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The role of the environment of an elliptical galaxy on its hot interstellar gas is discussed. In general, the X-ray halos of early-type galaxies tend to be smaller and fainter in denser environments, with the exception of group-central galaxies. X-ray observations show many examples of nearby galaxies which are undergoing gas stripping. On the other hand, most bright galaxies in clusters do manage to retain small coronae of X-ray emission. Recent theoretical and observational results on the role of feedback from AGN at the centers of elliptical galaxies on their interstellar gas are reviewed. X-ray observations show many examples of X-ray holes in the central regions of brightest-cluster galaxies; in many cases, the X-ray holes are filled with radio lobes. Similar radio bubbles are seen in groups and individual early-type galaxies. “Ghost bubbles” are often seen at larger radii in clusters and galaxies; these bubbles are faint in high radio frequencies, and are believed to be old radio bubbles which have risen buoyantly in the hot gas. Low frequency radio observations show that many of the ghost bubbles have radio emission; in general, these long wavelength observations show that radio sources are much larger and involve greater energies than had been previously thought. The radio bubbles can be used to estimate the total energy output of the radio jets. The total energies deposited by radio jets exceed the losses from the gas due to radiative cooling, indicating that radio sources are energetically capable of heating the cooling core gas and preventing rapid cooling.
KeywordsRadio Source Cold Front Elliptical Galaxy Cool Core Radio Lobe
I thank Liz Blanton, Tracy Clarke, Judith Croston, and Ming Sun for comments and help with the figures for the original talk which led to this chapter. I want to thank Dong-Woo Kim and Silvia Pellegrini for organizing the very useful Joint Discussion at the IAU General Assembly in Rio, and for editing this volume. This work was supported by NASA Chandra grants GO7-8078X, GO7-8081A, GO8-9083X, GO8-9085X, GO9-0135X, and GO9-0148X, and NASA Herschel grant RSA1373266, and NASA HST grants HST-GO-10597.03-A and HST-GO-11679.01.
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