We study the possibility of quasar outflows in clusters and groups of galaxies heating the intracluster gas in order to explain the recent observation of excess entropy in this gas. We use the extended Press-Schechter formalism to estimate the number of quasars that become members of a group of cluster of a given mass and formation epoch. We also estimate the fraction of mechanical energy in the outflows that is imparted to the surrounding medium as a function of the density and temperature of this gas. We finally calculate the total amount of non-gravitational heating from such outflows as a function of the cluster potential and formation epoch. We show that outflows from broad absorption line (BAL) and radio loud quasars can provide the required amount of heating of the intracluster gas. We find that in this scenario most of the heating takes place at $z \sim 1\hbox{--}4$, and that this ``preheating'' epoch is at lower redshift for lower mass clusters.Comment: Latex (mn.sty), 8 figures, accepted for publication in the MNRA

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.

We investigate in detail the role of active galactic nuclei (AGN) on the physical state of the gas in galaxy groups and clusters, and the implications for anisotropy in the cosmic microwave background (CMB) from Sunyaev-Zeldovich (SZ) effect. We have recently showed that AGNs can significantly change the entropy of the intracluster medium (ICM) and explain the observations of excess entropy in groups and clusters. AGNs are assumed to deposit energy via buoyant bubbles which expand as they rise in the cluster atmosphere and do P dV work on the ICM. Here, we include the effect of thermal conduction, and find that the resulting profiles of temperature and entropy are consistent with observations. Unlike previously proposed models, our model predicts that isentropic cores are not an inevitable consequence of preheating. The model also reproduces the observational trend for the density profiles to flatten in lower mass systems.We deduce the energy E agn required to explain the entropy observations as a function of mass of groups and clusters M cluster and show that E agn ∝ M α cluster with α ∼ 1.5. We demonstrate that the entropy measurements, in conjunction with our model, can be translated into constraints on the cluster-black hole mass relation. The inferred relation is nonlinear and has the form M bh ∝ M α cluster . This scaling is an analog and extension of a similar relation between the black hole mass and the galactic halo mass that holds on smaller scales.In addition, we study the implications of these results for thermal SZ effect. We show that the central decrement of the CMB temperature is reduced due to the enhanced entropy of the ICM, and that the decrement predicted from the plausible range of energy input from the AGN is consistent with available data of SZ decrement. We also estimate the Poisson contribution to the angular power spectrum of the CMB from the SZ effect due to AGN heating. We show that AGN heating, combined with the observational constraints on entropy, leads to suppression of higher multipole moments in the power spectrum and we find that this effect is stronger than previously thought. The supression in the power spectrum in our model is due to depletion of gas from the central regions that is more efficient in low mass clusters and groups than in massive clusters.

We study the X‐ray cluster gas density distribution in hydrostatic equilibrium using the universal temperature profile obtained from recent simulations involving only gravitational processes. If this temperature profile is an indicator of the influence of gravitational processes alone on the intracluster medium (ICM), then the comparison of various X‐ray parameters expected from this profile and the observed data would point towards any additional physics that may be required. We compare the entropy at 0.1 R200 and R500, the scaled entropy profile, the gas fraction at 0.3 R200 and the gas fraction profile with recent observations and we discuss the implications of this temperature profile in light of these data. We find that the entropy imparted to the gas from gravitational processes alone is larger than previously thought. The entropy at R500 for rich clusters is consistent with the data, whereas the entropy at 0.1 R200 is still less than the observed values. We also find that the gas fraction in the inner region of clusters, expected from gravitational processes alone, is smaller than previously thought but larger than the observed data. It does show a trend with the emission‐weighted temperature (〈T〉) as shown by the data. We therefore find that the role of any additional non‐gravitational process influencing the physical state of ICM would have to be revised in light of these findings.

In this work we study the contribution of magnetic fields to the Sunyaev Zeldovich (SZ) effect in the intracluster medium. In particular we calculate the SZ angular power spectrum and the central temperature decrement. The effect of magnetic fields is included in the hydrostatic equilibrium equation by splitting the Lorentz force into two terms -one being the force due to magnetic pressure which acts outwards and the other being magnetic tension which acts inwards. A perturbative approach is adopted to solve for the gas density profile for weak magnetic fields (≤ 4µG). This leads to an enhancement of the gas density in the central regions for nearly radial magnetic field configurations. Previous works had considered the force due to magnetic pressure alone which is the case only for a special set of field configurations. However, we see that there exists possible sets of configurations of ICM magnetic fields where the force due to magnetic tension will dominate. Subsequently, this effect is extrapolated for typical field strengths (∼ 10µG) and scaling arguments are used to estimate the angular power due to secondary anisotropies at cluster scales. In particular we find that it is possible to explain the excess power reported by CMB experiments like CBI, BIMA, ACBAR at ℓ > 2000 with σ 8 ∼ 0.8 (WMAP 5 year data) for typical cluster magnetic fields. In addition we also see that the magnetic field effect on the SZ temperature decrement is more pronounced for low mass clusters ( T ∼ 2 keV). Future SZ detections of low mass clusters at few arc second resolution will be able to probe this effect more precisely. Thus, it will be instructive to explore the implications of this model in greater detail in future works.