Radio AGN in galaxy clusters: heating hot atmospheres and driving supermassive black hole growth over cosmic time. (arXiv:1206.7071v1 [astro-ph.CO]):
We estimate the average radio-AGN (mechanical) power deposited into the hot
atmospheres of galaxy clusters over more than three quarters of the age of the
Universe. Our sample was drawn from eight major X-ray cluster surveys, and
includes 685 clusters in the redshift range 0.1<z<0.6 that overlap the area
covered by the NVSS. The radio-AGN mechanical power was estimated by scaling
the radio luminosity of central NVSS radio sources using the relation between
the radio synchrotron luminosities and X-ray cavity power measurements of
Cavagnolo et al. (2010). We find only a weak correlation between radio
luminosity and cluster X-ray luminosity across the sample. This trend is driven
primarily by the most distant clusters, where the detection fraction and
average radio powers are higher in the most luminous X-ray clusters at
redshifts at or above z=0.3. The average AGN mechanical power of
$3\times10^{44}$ erg/s exceeds the X-ray luminosity of 44% of the clusters in
our sample, indicating that the accumulation of radio-AGN energy is significant
in these clusters. Integrating the AGN mechanical power to redshift z = 2.0,
using simple models for its evolution and disregarding the hierarchical growth
of clusters, we find that the AGN energy accumulated per particle in low
luminosity X-ray clusters exceeds 1.0 keV per particle. This conservative
estimate is comparable to the level of energy needed to "preheat" clusters,
indicating that continual outbursts from radio-AGN are a significant source of
gas energy in hot atmospheres. Our result implies that the supermassive black
holes in brightest cluster galaxies that generated this energy did so by
accreting an average of 10^9 M_sun over time, which is comparable to the rapid
level of growth expected during the quasar era.
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