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Astro Seminar

The edge of darkness: making sense of structure formation with the splashback radius

Speaker: Benedikt Diemer (Maryland)
Date: Wednesday 14 October 2020
Time: 14:00
Venue: Zoom

The size, mass, and evolution of dark matter halos impact virtually all areas of structure and galaxy formation. These properties are conventionally defined using somewhat arbitrary spherical overdensity radii, largely because halo profiles are thought not to have a well-defined edge. Over the past years, we have shown that halos do have such an edge: the splashback boundary, which has since been detected in a number of galaxy surveys. Redefining halo properties based on this boundary has profound consequences for numerous problems in structure formation and facilitates a new understanding of the dynamical nature of halos. In this talk, I will introduce the tools necessary to make this transition. I will introduce an analysis framework that follows the dynamics of billions of particles in cosmological simulations, and present a new suite of publicly available halo catalogs for the exploration of halo definitions. First results based on this dataset include that the splashback halo mass function is remarkably universal and that the abundance of subhalos (or satellites) is drastically changed. These results open a window on the possibility of using future observations of the halo outskirts to constrain the galaxy-halo connection, cosmology, and the nature of dark matter.