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Extreme AGN feedback in the MAssive Cluster Survey: a detailed study of X-ray cavities at z>0.3




We present the first statistical study of X-ray cavities in distant clusters of galaxies (z > 0.3). With the aim of providing further insight into how active galactic nucleus (AGN) feedback operates at higher redshift, we have analysed the Chandra X-ray observations of the MAssive Cluster Survey (MACS) and searched for surface brightness depressions associated with the brightest cluster galaxy (BCG). The MACS sample consists of the most X-ray luminous clusters within 0.3 ≤z≤ 0.7 (median LX, RASS= 7 × 1044 erg s−1), and out of 76 clusters, we find 13 with ‘clear’ cavities and seven with ‘potential’ cavities (detection rate ∼25 per cent). Most of the clusters in which we find cavities have a short central cooling time below 3–5 Gyr, consistent with the idea that cavities sit predominantly in cool core clusters. We also find no evidence for evolution in any of the cavity properties with redshift, up to z∼ 0.6. The cavities of powerful outbursts are not larger (or smaller) at higher redshift, and are not able to rise to further (or lesser) distances from the nucleus. The energetics of these outbursts also remain the same. This suggests that extreme ‘radio mode’ feedback (Lmech > 1044 erg s−1) starts to operate as early as 7–8 Gyr after the big bang and shows no sign of evolution since then. In other words, AGNs lying at the centre of clusters are able to operate at early times with extreme mechanical powers, and have been operating in such a way for at least the past 5 Gyr.