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
... 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 iii 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. iv Acknowledgements As with any involved, long term endeavor, this work and all the work leading up to it does not solely result from the effort of one individual. It is only made possible with the help of a supportive community, in terms of its history, culture, and most importantly all the people that carry on those traditions. I cannot adequately thank or acknowledge all those deserving mention, nor will I attempt to, but I will offer that it would be a great understatement to say the bootstraps by which I have pulled myself up were well made by those that came before and well maintained by those that came with me on this journey. First, I must admit that none of the research presented herein would have happened without the ideas, insight, dedication, and all-around awesomeness of my mentor, Craig Sarazin. His distinguished career, which includes literally writing the book on galaxy clusters, has lead the field for decades and been an excellent guide for me for, thankfully, not quite so long. I have to credit Craig for the majority of my professional development, both scientifically and practically, which is due in no small part to his incredible openness, accessibility, and willingness to pause whatever he is doing if you pop into his office to chat. I look forward to working with Craig for years to come. But neither this work, his work, or any of the discoveries in X-ray astronomy would have been possible without the generous public support necessary to launch our instruments and telescopes into orbit. Specifically, I am indebted to the creators and funders of projects like Chandra, XMM-Newton, Suzaku, and Swift, with which the data presented here was gathered. These missions allow us to understand our place in the universe, in my opinion providing a context for finding meaning in life, both for individuals and the human race as a whole. I am proud to live in a society v that values such endeavors and understands how valuable and inspiring exploration is. Also, I am proud that this field is full of so many dedicated and brilliant fellow scientists, and it has been my pleasure to collaborate with them; I decline to list them here so you will look up the papers that derive from the following chapters and hopefully discover all the fine work they have done elsewhere as well.