The Chandra X-ray Observatory allows us to study nearby clusters, such as the Perseus cluster, in exquisite detail. These deep observations reveal a wealth of structure, including bubbles inflated by radio jets, ripples in the intracluster plasma caused by traveling sound waves, and discontinuities in the gas caused by shocks and traveling cold fronts. As we extend our observations to higher redshift, our ability to resolve these detailed structures greatly diminishes, though much information still remains in the large scale morphology.

In the past decade, the number of known galaxy clusters at large distances (z > 1) has increased dramatically, from a handful of exotic systems to well-characterized samples of ~100 clusters. These systems, discovered primarily via the Sunyaev Zel’dovich effect, provide a glimpse into a much earlier phase of structure formation, when clusters were first assembling, massive galaxies were still forming, and black hole feedback was just turning on.

In collaboration with the South Pole Telescope (SPT) and Massive and Distant Clusters of Wise (MaDCoWs) surveys, we have identified hundreds of clusters at high redshift that we are in the process of following up in the X-ray, using the Chandra and XMM-Newton telescopes. At these large distances, clusters are extremely faint, making X-ray analyses challenging. We lean on multi-wavelength data and optical, infrared, mm, and radio to assist in our interpretation of subtle X-ray features, and also develop in-house analysis tools to get the most out of these data. Equally important is asking the right questions, which are addressable with current-generation facilities, while also helping to plan and develop next-generation instrumentation. The primary questions we are attempting to answer are:

• When did galaxy clusters first collapse, virialize, and dynamically relax?
• When was the intracluster medium first enriched with metals?
• When did cooling of the intracluster medium become important? When did cool cores form?
• When was “self similarity” of thermodynamic profiles established?

Below are some relevant papers and links to ongoing collaborations/efforts.

• “The Future Landscape of High-Redshift Galaxy Cluster Science”, Mantz, M., et al., 2020 Decadal White Paper
• “Stability of Cool Cores During Galaxy Cluster Growth: A Joint Chandra/SPT Analysis of 67 Galaxy Clusters Along a Common Evolutionary Track Spanning 9 Gyr”, Ruppin F., McDonald M., et al., 2020, arXiv, arXiv:2012.14669
• “The Remarkable Similarity of Massive Galaxy Clusters from z ∼ 0 to z ∼ 1.9”, McDonald M., et al., 2017, ApJ, 843, 28
• “The Evolution of the Intracluster Medium Metallicity in Sunyaev Zel’dovich-selected Galaxy Clusters at 0 < z < 1.5”, McDonald M., et al., 2016, ApJ, 826, 124
• The South Pole Telescope Project