Inverse Compton scattering in galaxy clusters

Clusters of galaxies are the largest relaxed structures in the universe and are very important cosmological probes. The state of the intracluster medium (ICM) of galaxy clusters, under the hydrostatic assumption, can be used to infer their masses, the distribution of which can be used to constrain cosmological parameters. Thus, it is important to assess the accuracy of ICM-derived masses. Two phenomena that can bias mass estimates are major cluster mergers, which temporarily removes the ICM from hydrostatic balance, and the existence of energetically significant nonthermal phases of the ICM. In the case of major mergers, we investigate their impact on the measurements of the Sunyaev-Zel'dovich effect which will be used to produce mass estimates. The central (maximum) Comptonization parameter is severely boosted at a level which is similar to the X-ray temperature and luminosity, which leads to several tens of percent bias in cosmological parameters. On the other hand, the integrated Comptonization parameter is found to be robust to mergers, allowing the dark energy equation of state to be accurately determined. Regarding the nonthermal phase of the ICM, we aim to test previous detections of inverse Compton (IC) emission and to make new ones. Taken in conjunction with detected radio synchrotron emission, the relativistic energy content of the ICM can be assessed. We search for IC emission, in the Coma cluster with a detailed analysis of data from two hard X-ray sensitive satellites, Suzaku and Swift , and complimentary data from XMM-Newton. We do not detect IC emission, and our upper limits exclude the previous detections at the ≳ 90% level. The Swift BAT observations also exclude the possibility that Coma has very strong but very extended IC emission. Similarly, no significant IC emission is detected in spectra from the Swift BAT survey of a sample (HIFLUGCS) of the brightest X-ray clusters, in contrast to expectations based on the results of previous searches. A weak detection of IC emission from clusters with radio halos and relics is found from the Swift survey. The implications of this work, along with future prospects, are also discussed.