Investigating AGN heating in a sample of nearby clusters

We analyse those objects in the Brightest 55 sample of clusters of galaxies which have a short central cooling time and a central temperature drop. Such clusters are likely to require some form of heating. Where clear radio bubbles are observed in these clusters, their energy injection is compared to the X‐ray cooling rate. Of the 20 clusters requiring heating, at least 14 have clear bubbles, implying a duty cycle for the bubbling activity of at least 70 per cent. The average distance out to which the bubbles can offset the X‐ray cooling, r heat , is given by r heat / r cool = 0.86 ± 0.11 where r cool is defined as the radius as which the radiative cooling time is 3 Gyr. 10 out of 16 clusters have r heat / r cool ≳ 1 , but there is a large range in values. The clusters which require heating but show no clear bubbles were combined with those clusters which have a radio core to form a second subsample. Using r heat = 0.86 r cool we calculate the size of an average bubble expected in these clusters. In five cases (3C129.1, A2063, A2204, A3112 and A3391) the radio morphology is bi‐lobed and its extent similar to the expected bubble sizes. A comparison between the actual bubble size and the maximum expected if they were to offset the X‐ray cooling exactly, R max , shows a peak at R bubble ∼ 0.7 R max with a tail extending to larger R bubble / R max . The offset from the expected value of R bubble ∼ R max may indicate the presence of a non‐thermal component in the innermost intracluster medium of most clusters, with a pressure comparable to the thermal pressure.