AGN heating in complete samples of galaxy clusters

The Chandra X-ray Observatory has revealed X-ray cavities in many nearby cooling flow clusters. The cavities trace feedback from the central active galactic nucleus (AGN) on the intracluster medium (ICM), an important ingredient in stabilizing cooling flows and in the process of galaxy formation and evolution. But, the prevalence and duty cycle of such AGN outbursts is not well understood. To this end, we study how the cooling is balanced by the cavity heating for complete samples of clusters (the Brightest 55 clusters of galaxies, hereafter B55, and the HIghest X-ray FLUx Galaxy Cluster Sample, HIFLUGCS). In each sample, we found 35 cooling flow clusters (with min(kT/ (Lambda nenHr2)) <slant 5 ), of which 22 for B55 and 23 for HIFLUGCS have detected X-ray bubbles in their ICM. Among the remaining systems, all except Ophiuchus could have significant cavity power yet remain undetected in existing images. This implies that the duty cycle of AGN outbursts with significant heating potential in cooling flow clusters is at least 60% and could approach 100%, but deeper data is required to constrain this further.