Astro Lunch

Characterising and Identifying Galaxy Protoclusters

Galaxy protoclusters are the pre-collapse progenitors of today's massive clusters. They trace overdensities of dark matter with respect to the field, which manifest as visible overdensities in the galaxy population. At z> 2 they cover a large spatial area (> 20 Mpc in width) which corresponds to a large fraction of the sky, contribute significantly to the cosmic star formation rate density, and host some of the most massive and highly star forming galaxies in the universe at these times. It is therefore important to be able to reliably identify protoclusters in high redshift observations, and understand how their high redshift properties relate to their descendant cluster properties. I will talk about a new procedure we have developed for identifying protoclusters, using the L-galaxies semi-analytic model, that takes in to account the purity and completeness of the protocluster galaxy population.