Physics & Astronomy Colloquium – Fall 2020 – Walker
September 23 @ 3:30 pm - 5:00 pm
Speaker: Stephen Walker (UA Huntsville)
Title: Galaxy Cluster Outskirts: Pushing Back the Final Frontier in Cluster Astrophysics
Abstract: As the largest virialized structures in the universe, galaxy clusters continue to grow and accrete matter in their outskirts from the cosmic web which connects them together. Due to the low gas density in the outskirts, measurements are very challenging, requiring extremely sensitive telescopes across the entire electromagnetic spectrum. Until recently we have only been able to see the tip of the iceberg of galaxy clusters: the majority of their volume in the outskirts has remained hidden, along with the physical processes occurring there. Understanding the properties of the cluster outskirts is vital for unraveling the history of large scale structure formation in the universe, and for accurately using clusters as probes of cosmological parameters. Observations using X-rays, the Sunyaev–Zeldovich effect, and weak lensing and galaxy distributions from the optical band, have helped us to start to unravel this exciting new frontier of cluster astrophysics, where the infall and virialization of matter takes place. In this talk I will discuss the current state of the art in our observational and theoretical understanding of cluster outskirts, and the unexpected discoveries that have been made. Looking towards the future, I will outline observational strategies using existing and upcoming observatories that will allow galaxy clusters to be revealed in their full glory for the first time.
Speaker Biography: I did my PhD at the University of Cambridge, and stayed there afterwards for my first postdoc. I then moved to be a NASA Postdoctoral Program (NPP) Fellow at NASA’s Goddard Space Flight Center. In the summer of 2019, I started as an Assistant Professor of Physics and Astronomy at the University of Alabama in Huntsville (UAH). My research concentrates on all aspects of galaxy clusters (the largest collapsed structures in the universe), from the outskirts where they are continuing to form from the cosmic web, to gas sloshing produced by galaxy cluster mergers, to studying AGN feedback in cluster cores, focusing on their X-ray emission.