Measuring the mass profile of galaxy clusters beyond their virial radius

TL;DR

This paper reviews the caustic technique for measuring galaxy cluster mass profiles beyond the virial radius, highlighting its basis, performance, and applicability at various redshifts.

Contribution

It provides a comprehensive review of the caustic method, emphasizing its advantages over traditional equilibrium-based estimators and its potential for wide redshift application.

Findings

Caustic technique measures mass using galaxy positions and redshifts.

It can be applied to clusters at any redshift.

The method performs well beyond the virial radius.

Abstract

Traditional estimators of the mass of galaxy clusters assume that the cluster components (galaxies, intracluster medium, and dark matter) are in dynamical equilibrium. Two additional estimators, that do not require this assumption, were proposed in the 1990s: gravitational lensing and the caustic technique. With these methods, we can measure the cluster mass within radii much larger than the virial radius. In the caustic technique, the mass measurement is only based on the celestial coordinates and redshifts of the galaxies in the cluster field of view; therefore, unlike lensing, it can be, in principle, applied to clusters at any redshift. Here, we review the origin, the basics and the performance of the caustic method.