Abstract

Contributed Talk - Splinter GalaxyClusters

Tuesday, 08 September 2026, 16:35   (MW-1050)

Testing observational protocluster searches with MillenniumTNG

Eileen Herwig
Max Planck Institute for Astrophysics

The detection of new protoclusters often relies on photometric observations targeting specific galaxy populations such as submillimeter galaxies, Lyman-alpha emitters, or Lyman-break galaxies, but how reliably overdensities of these tracers identify the progenitors of today's massive clusters remains unclear. I use the MillenniumTNG simulation, which combines full hydrodynamics with a large box size of 740 Mpc and therefore a statistical sample of more than 4000 galaxy clusters, to model the three populations, match common observational approaches and quantify their protocluster identification performance across z=1-7. I find that different tracers occupy very different corners of the precision-completeness space, and that the measured overdensity is a surprisingly weak predictor of descendant halo mass, calling into question calibrations from semi-analytical models that are widely used to infer cluster masses from observed overdensities. These results offer a simulation-based framework to interpret detected overdensities and assess their likelihood of evolving into a massive galaxy cluster, and can serve as guidance for the design and analysis of upcoming wide-field surveys.