The Triaxial Cow: Measuring the 3D Shapes of Galaxy Clusters

Adriana Gavidia, Observational Cosmology / Caltech

Galaxy clusters are the largest and most recently formed objects in the universe, making them rich laboratories to test the astrophysics of structure formation and cosmology. Within the current standard cosmological framework, structure formation is pictured as a hierarchical merging process, where clusters form from the gravitational collapse of the most dense peaks in the initial primordial density field. A triaxial collapse is a direct prediction of structure growth driven by the self-gravity of Gaussian density fluctuations. As large scale structure evolves, tidal forces from the most massive peaks guide the surrounding matter into massive filamentary structures, connecting the clusters to one another to form a foam-like structure called the “cosmic web”. Numerical simulations indicate that new matter is accreted onto clusters preferentially along these filaments, leading to an alignment between the major axis of the cluster mass halo and the large-scale filament, giving clusters an intrinsically aspherical morphology. This prediction is supported by evidence from various observational probes such as X-ray, Sunyaev-Zeldovich Compton-y, and gravitational lensing. Despite this, until recently studies have taken the infamous “spherical cow” approach to model cluster morphology, as data quality and the lack of availability of multi-wavelength data sets limited the ability to perform triaxial analyses. To obtain less biased measurements of the cluster properties used to constrain cosmology, it is crucial we upgrade to the “triaxial cow” model. In this talk, I will present our triaxial modeling technique enabled by the high quality multi-probe data set collected for the CHEX-MATE collaboration and the science we can extract from these measurements.

Host: Kane