Tracing the Dynamical States of Intracluster Media (ICMs)

The universe has assembled itself by gravity into objects from the size of planets and stars up to galaxies and, on the largest scales, clusters of galaxies. The investigators will focus on understanding the formation of these clusters, giving us important insights into the entire process of how objects form. Galaxy clusters can contain hundreds of galaxies and are filled with very hot gas - their atmospheres, or 'intracluster media'. These atmospheres are so hot that most of the light they emit is X-rays that can be seen only from space. Astronomers have established that this hot gas has often been highly disturbed when one cluster violently collides and merges with another cluster. The gas motions can tell us about the collisions and how these largest structures in the universe form. Space X-ray telescopes are limited in their abilities to trace these motions, especially outside the denser cluster centers. As it turns out, however, galaxies scattered throughout clusters spew out streams of highly energetic particles that emit radio waves visible from the earth that reveal their interactions with the intracluster media. The intracluster gas motions can also energize radio emitting particles, illuminating the motions. The investigators will find these radio emissions and map their details, using both new and existing ground based radio telescope observations and utilizing the citizen-science-based 'Radio Galaxy Zoo.' In addition, they will compute detailed physical models to determine how these emissions can be used to trace out the motions of the intracluster media as well as their origins and histories. The results of these studies will substantially improve our understanding of how galaxy clusters form.

Galaxy clusters are the largest known gravitationally bound systems in the universe. They are filled with 'intracluster media,' diffuse plasmas with temperatures of 10s of millions of degrees, which are visible from space using X-rays. The investigators will address three key questions about these media: 1) what is the dynamical state of the gas, its flows, turbulence and shocks? 2) how do these dynamical features help us understand the cluster formation process? and 3) how do we reliably connect the underlying motions with what we can observe? The investigators will specifically concentrate on behaviors observable at radio wavelengths, using emission from electrons moving at relativistic speeds in the presence of a magnetic field. This allows them to study regimes such as cluster outskirts, for which very little X-ray information is available. They will carry out numerical simulations at the technical frontier, coupling the magnetohydrodynamics of the hot gas to the relativistic particles generating the radio emission. They will conduct new state-of-the-art radio telescope observations and analyses, along with information from the citizen science project Radio Galaxy Zoo on distortions of radio-emitting plasmas caused by the hot gas flows. Together, this work will enable the investigators to gain important information about the cluster formation process, a key piece in the universal picture of how structures in the universe develop over billions of years.