Using the outskirts of galaxy clusters to determine their mass accretion rate

TL;DR

This paper proposes a new observational method to measure galaxy cluster mass accretion rates using the outer regions of clusters, validated against simulations, enabling insights into cosmic structure growth.

Contribution

It introduces a novel approach to estimate cluster MAR from the mass profile beyond the splashback radius, linking observations with simulation data.

Findings

MAR estimates are within 20-40% of simulation-based values.

The method is applicable across redshifts z=[0, 2].

External cluster regions can reliably indicate average MAR.

Abstract

We explore the possibility of using the external regions of galaxy clusters to measure their mass accretion rate (MAR). The main goal is to provide a method to observationally investigate the growth of structures on the nonlinear scales of galaxy clusters. We derive the MAR by using the mass profile beyond the splashback radius, evaluating the mass of a spherical shell and the time it takes to fall in. The infall velocity of the shell is extracted from $N$-body simulations. The average MAR returned by our prescription in the redshift range $z=[0, 2]$ is within $20-40 \%$ of the average MAR derived from the merger trees of dark matter haloes in the reference $N$-body simulations. Our result suggests that the external regions of galaxy clusters can be used to measure the mean MAR of a sample of clusters.