The Role of Non-Equilibrium Processes in Galaxy Clusters

Wong, Ka-Wah, Department of Astronomy, University of Virginia
Sarazin, Craig, Department of Astronomy, University of Virginia

This thesis studies non-equilibrium processes in clusters of galaxies. On a small scale, we studied observationally a cooling core cluster with AGN feedback; on a large scale, we studied theoretically non-equilibrium processes in cluster accretion shock regions. XMM-Newton and Chandra observations of Abell 2626 are presented. We do not find an obvious correlation between the radio bars and the X-ray image. We suggest that the two symmetric radio bars can be explained by two precessing jets ejected from an AGN. We argue that Abell 2626 is preferentially accreting subclusters and groups from large-scale structure filaments. We also find evidence that the S0 galaxy IC 5337 is infalling toward the cluster center from the west. Electrons and ions which pass through an accretion shock may not achieve equipartition due to the long Coulomb collisional timescale in the low density environment. We have studied the non-equipartition effects in the outer regions of relaxed clusters using one-dimensional hydrodynamic simulations. We find that in the ΛCDM universe, non-equipartition effects are larger for clusters at higher redshifts and with higher masses. We also present in detail the X-ray and Sunyaev–Zel'dovich (SZ) signatures of non-equipartition. The impact of non-equipartition effects on cosmological parameter estimation from SZ surveys is studied. We find that non-equipartition can bias the cosmological parameters Ω M , σ 8 , and the dark energy equation of state parameter w by a few percent. In particular, non-equipartition effects can introduce an apparent evolution in w. Non-equilibrium ionization (NEI) effects in the outer regions of relaxed clusters are also studied. We find that NEI effects do not depend on cluster mass but iniv crease as redshift decreases, which can be understood by self-similar arguments. The most prominent NEI signature we found is the O VII and O VIII line ratio, which is different by more than an order of magnitude for NEI and collisional ionization equilibrium (CIE) models at radii beyond half of the shock radius. We conclude that a ∼130–220 ksec exposure on a moderate-redshift, massive regular cluster with the International X-ray Observatory (IXO) should provide a strong test for the NEI model by measuring this line ratio.

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PHD (Doctor of Philosophy)
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