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Galaxy Evolution and AGN

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Composite image of the massive galaxy cluster M87 shows X-ray data from the Chandra X-ray Observatory in blue, and a radio image from the VLA in red.

Classical models of galaxy formation predict that the largest galaxies should be bigger and brighter than we observe. Our team and others have argued that supermassive black holes in the centers of galaxies may be responsible, largely or in part, for this suppressed growth. The regions close to black holes can pump out huge amounts of energy in relativistic jets, which inflate cavities in the surrounding gas, driving shock waves and turbulent motions. Using X-ray and radio observations, we have shown that this mode of "feedback" occurs with a high and near-universal efficiency in the most massive galaxies, and that turbulent heating driven by this mode may balance radiative cooling. 

The mechanisms that trigger supermassive black hole activity remain the subject of debate. One way we explore this is by studying the frequency of AGN activity within clusters, which contain large numbers of galaxies in close proximity (which enhances tidal encounters and mergers between galaxies) and are pervaded by hot diffuse gas (which causes ram pressure stripping). Other methods we employ include studying the statistical relationships between AGN and the properties of their host galaxies using clustering measurements, and observing the frequency of AGN activity in close double and triple galaxy systems.

For further discussion of this work, see e.g.: