Entropy “Floor” and Effervescent Heating of Intracluster Gas

Abstract

Recent X-ray observations of clusters of galaxies have shown that the entropy of the intracluster medium (ICM), even at radii as large as half the virial radius, is higher than that expected from gravitational processes alone. This is thought to be the result of nongravitational processes influencing the physical state of the ICM. In this paper, we investigate whether heating by central AGN can explain the distribution of excess entropy as a function of radius. The AGN are assumed to inject buoyant bubbles into the ICM, which heat the ambient medium by doing pdV work as they rise and expand. Several authors have suggested that this "effervescent heating" mechanism could allow the central regions of clusters to avoid the "cooling catastrophe". Here we study the effect of effervescent heating at large radii. We find that the results are mainly sensitive to the total energy injected into the cluster. Our calculations show that such a heating mechanism is able to solve the entropy problem, provided that the total energy injected by AGN is roughly proportional to the cluster mass. The inferred correlation is consistent with a linear relation between the mass of the central black hole(s) and the mass of the cluster, which is reminiscent of the Magorrian relation between the black hole and bulge mass.

Heating groups and clusters of galaxies: The role of AGN jets

“…In this plot is even more evident that a good agreement with the data is obtained only with the higher power energy injections at the smaller scales (T ew < 1 keV). This is not surprising: it has been argued by Roychowdhury et al (2004) that an energy injection which increases linearly with the cluster mass is needed to reproduce the entropy profiles observed by Ponman et al (2003): on the other hand we are injecting the same amount of energy at all scales which does not seem to be enough for the more massive clusters. …”

The diversity of growth histories of Milky Way-mass galaxies

“…The galaxy heats up its atmosphere via jets from the accretion onto the black hole. There are many theories that attempt to explain the exact mechanism by which the atmosphere is heated, whether it be shocks due to an AGN jet injecting energy into the atmosphere (Fabian et al, 2005;Blanton et al, 2009;Randall et al, 2011), cosmic ray heating from the jet (Sijacki et al, 2008;Guo & Oh, 2008), or effervescent heating from buoyant bubbles in the ICM (Begelman, 2001;Roychowdhury et al, 2004;Voit & Donahue, 2005;), but the current status of these studies is inconclusive. In H15, AGN heating is extremely simplified where the AGN provides a heating rate which depends on the hot gas mass and the mass of the black hole.…”

Filaments, Bubbles, and Weak Shocks in the Gaseous Atmosphere of M87

“…These bubbles can be a significant energy source for the cooling gas and can explain much of the radio and X-ray morphology (Churazov et al 2001Quilis et al 2001;Brüggen et al 2002). The energy of jets and buoyant bubbles can be transferred to the radiating gas by shocks, gravity waves, or turbulence (e.g., Churazov et al 2002;Ruszkowski et al 2004aRuszkowski et al , 2004bBegelman 2004;Omma et al 2004;Roychowdhury et al 2004Roychowdhury et al , 2005Heinz & Churazov 2005;Mathews et al 2006;Binney et al 2007). From deep Chandra observations of the Perseus Cluster, Fabian et al (2006) showed that pressure ripples could balance radiative cooling in the Perseus core, if the viscosity is high.…”