Is there substructure around M87?

TL;DR

The paper introduces a novel method to detect infalling substructures around galaxies by analyzing their energy distributions, successfully applied to M87's satellite system, revealing potential galaxy groups in infall.

Contribution

It develops a new approach extending Eddington's formula to identify infalling groups using energy distribution analysis in galaxy datasets.

Findings

Identified potential infalling galaxy groups around M87.

Validated the method with mock data.

Detected associations that may be infalling groups.

Abstract

We present a general method to identify infalling substructure in discrete datasets with position and line-of-sight velocity data. We exploit the fact that galaxies falling onto a brightest cluster galaxy (BCG) in a virialised cluster, or dwarf satellites falling onto a central galaxy like the Milky Way, follow nearly radial orbits. If the orbits are exactly radial, we show how to find the probability distribution for a satellite's energy, given a tracer density for the satellite population, by solving an Abel integral equation. This is an extension of Eddington (1916)'s classical formula for the isotropic distribution function. When applied to a system of galaxies, clustering in energy space can then be quantified using the Kullback-Leibler divergence, and groups of objects can be identified which, though separated in the sky, may be falling in on the same orbit. This method is tested using mock data and applied to the satellite galaxy population around M87, the BCG in Virgo, and a number of associations are found which may represent infalling galaxy groups.