Reflections of Active Galactic Nucleus Outbursts in the Gaseous Atmosphere of M87

We combined deep Chandra, ROSAT HRI, and XMM-Newton observations of M87 tostudy the impact of AGN outbursts on its gaseous atmosphere. Many X-rayfeatures appear to be a direct result of repetitive AGN outbursts. Inparticular, the X-ray cavities around the jet and counter jet are likely due tothe expansion of radio plasma, while rings of enhanced emission at 14 and 17kpc are probably shock fronts associated with outbursts that began1-2\times10^7 years ago. The effects of these shocks are also seen inbrightenings within the prominent X-ray arms. On larger scales, ~50 kpc fromthe nucleus, depressions in the surface brightness may be remnants of earlieroutbursts. As suggested for the Perseus cluster (Fabian et al.), our analysisof the energetics of the M87 outbursts argues that shocks may be the mostsignificant channel for AGN energy input into the cooling flow atmospheres ofgalaxies, groups, and clusters. For M87, the mean power driving the shockoutburst, 2.4\times 10^{43} ergs/sec, is three times greater than the radiativelosses from the entire ``cooling flow''. Thus, even in the absence of otherenergy inputs, outbursts every 3\times10^7 years are sufficient to quench theflow.Comment: Several references adde