Mon. Not. R. Astron. Soc., 373, 959-971 (2006/December-2)
Investigating AGN heating in a sample of nearby clusters.
DUNN R.J.H. and FABIAN A.C.
Abstract (from CDS):
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, rheat, is given by rheat/rcool= 0.86±0.11 where rcoolis defined as the radius as which the radiative cooling time is 3Gyr. 10 out of 16 clusters have rheat/rcool ≳ 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 rheat= 0.86rcoolwe 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, Rmax, shows a peak at Rbubble∼ 0.7Rmaxwith a tail extending to larger Rbubble/Rmax. The offset from the expected value of Rbubble ∼ Rmaxmay indicate the presence of a non-thermal component in the innermost intracluster medium of most clusters, with a pressure comparable to the thermal pressure.