Camille Avestruz

The observational study of galaxy cluster outskirts is a new territory to probe the thermodynamic and chemical structure of the X-ray emitting intracluster medium (ICM) and the intergalactic medium (IGM). Cluster outskirts are particularly important for modeling the Sunyaev-Zel’dovich effect, which is sensitive to hot electrons at all radii and has been used to detect hundreds of galaxy clusters to high-redshift (z<1) with recent microwave cluster surveys such as ACT, Planck, and SPT. In cluster-based cosmology, measurements of cluster outskirts are an important avenue for estimating the cluster mass, as the outskirts are less sensitive to astrophysical uncertainties associated with gas cooling, star formation, and energy injection from supermassive black holes. However, recent observations of cluster outskirts deviate from theoretical expectations, indicating that cluster outskirts are more complicated than previously thought. For instance, recent observations from Suzaku X-ray satellite showed clusters with flat entropy profiles and gas fractions exceeding the cosmic baryon fraction at large radii. Computational modeling of cluster outskirts is necessary to interpret these observations. In my dissertation, I present hydrodynamical cosmological simulations of galaxy cluster formation that follow the thermodynamic and chemical structures in the virialization regions of the ICM and transition to the IGM. Specifically, I show how observational signatures of galaxy clusters are affected by (a) gas density and temperature inhomogeneities in the ICM due to infalling gas clumps and large-scale filaments, and (b) non-equilibrium electrons generated by accretion shocks at the outer boundary of clusters. As an example of how this work is directly relevant for observations, I will discuss implications for recent ultra-deep Chandra XVP observations of Abell 133.