Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..12e...9w&link_type=abstract
Long Wavelength Astrophysics, 26th meeting of the IAU, Joint Discussion 12, 21 August 2006, Prague, Czech Republic, JD12, #9
Astronomy and Astrophysics
Astrophysics
Scientific paper
Recent X-ray and radio data on clusters of galaxies clearly demonstrate the profound impact of AGN in cluster cores on the surrounding intracluster medium (ICM). The realization that powerful outbursts from AGN can release upwards of 10^61 erg into the ICM suggests a common solution to several cooling related issues long associated with clusters and groups of galaxies. AGN feedback has emerged as the most likely mechanism for regulating not only the cooling of the hot gas in clusters, but also the growth of the central cD galaxies themselves and their attendant super-massive black holes. In a number of clusters, deeper X-ray observations have revealed systems of cavities extending to large radii (~0.4 Mpc). Analogous to the smaller cavities seen previously, low frequency radio observations clearly show that these large-scale cavities are also filled with relativistic plasma apparently associated with earlier episodes of AGN activity. Here we present X-ray and radio data for several of these large-scale cavity systems and discuss the limits they place on the age, total energy output, and duty-cycle of activity for the central AGN. The mechanical energy necessary to inflate these super-cavities is ~10^61 ergs and the buoyant rise times imply ages for the cavities of 50-300 Myr. The clear implication is that we are seeing the fossil record of the accumulated energy output of the central AGN in clusters over the last ~300 Myr. The combination of deep X-ray imaging and low frequency radio data provide some of the most reliable and accurate diagnostics for determining the ages, energetics, and activity cycles of AGN in clusters. As we show, synchrotron power alone can underestimate the energetic output of AGN by orders of magnitude. We also discuss the implications these data have for the growth of super-massive black holes and models of galaxy formation. Finally we briefly discuss the possibilities for studying these systems in greater number and detail with emerging low frequency instruments such as LOFAR.
Birzan Laura
McNamara Brian R.
Nulsen Paul E. J.
Rafferty David A.
Wise Michael Wayne
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