Measuring the growth of galaxy clusters

TL;DR

This paper proposes using the caustic technique on dense redshift surveys to measure galaxy cluster mass growth beyond the virial radius, providing a new way to test structure formation models.

Contribution

It introduces a method to estimate cluster mass accretion rates and substructure fractions using the caustic technique on non-equilibrium regions.

Findings

Caustic technique can identify substructures with >60% completeness.

Mass profiles beyond virial radius can estimate mass accretion rates.

Substructure catalogs include masses >10^{13}h^{-1}M_\odot.

Abstract

We suggest how we can use the mass profile of galaxy clusters beyond their virial radius to measure their mass accretion rate, a key prediction of structure formation models. The mass profile can be estimated by applying the caustic technique to dense redshift surveys of clusters and their outskirts, where dynamical equilibrium does not necessarily hold. An additional probe of the mass growth of clusters is their mass fraction in substructures. We show that the caustic technique, that identifies cluster substructures as a by-product, returns catalogs of substructures with mass larger than a few $10^{13}h^{-1}M_\odot$ that are between 60% and 80% complete, depending on the density of the redshift survey.