NED Abstract 
Copyright by Royal Astronomical Society.
2012MNRAS.427.3468B

The duty cycle of radio-mode feedback in complete samples of clusters

Birzan, L.; Rafferty, D. A.; Nulsen, P. E. J.; McNamara, B. R.;
Rottgering, H. J. A.; Wise, M. W.; Mittal, R.

Abstract. The Chandra X-ray Observatory has revealed X-ray bubbles in the
intracluster medium (ICM) of many nearby cooling-flow clusters. The
bubbles trace feedback that is thought to couple the central active
galactic nucleus (AGN) to the ICM, helping to stabilize cooling flows and
govern the evolution of massive galaxies. However, the prevalence and duty
cycle of such AGN outbursts is not well understood. To this end, we study
how cooling is balanced by bubble heating for complete samples of clusters
(the Brightest 55 clusters of galaxies, hereafter B55, and the HIghest
X-ray FLUx Galaxy Cluster Sample, HIFLUGCS). We find that the radio
luminosity of the central galaxy only exceeds 2.5 x 10^30^ erg s^-1^
Hz^-1^ in cooling-flow clusters. This result implies a connection between
the central radio source and the ICM, as expected if AGN feedback is
operating. Additionally, we find a duty cycle for radio-mode feedback, the
fraction of time that a system possesses bubbles inflated by its central
radio source, of >~69 per cent for the B55 and >~63 per cent for the
HIFLUGCS. These duty cycles are lower limits since some bubbles are likely
missed in existing images. We used simulations to constrain the bubble
power that might be present and remain undetected in the cooling-flow
systems without detected bubbles. Among theses systems, almost all could
have significant bubble power. Therefore, our results imply that the duty
cycle of AGN outbursts with the potential to heat the gas significantly in
cooling-flow clusters is at least 60 per cent and could approach 100 per
cent. 

Key words: radio continuum: galaxies, X-rays: galaxies: clusters