Is there substructure around M87?

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.

9 pages, 6 figures, 2 tables. Accepted for publication in MNRAS

References in corpus (12)

• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
• The shapes, orientation, and alignment of Galactic dark matter subhalos
• The Extended Virgo Cluster Catalog
• The virialized mass of dark matter haloes
• Disassembling the Galaxy with angle-action coordinates
• The distribution function of dark matter in massive haloes
• The build-up of the cD halo of M87 - evidence for accretion in the last Gyr
• Action-space clustering of tidal streams to infer the Galactic potential
• Predicted Space Motions for Hypervelocity and Runaway Stars: Proper Motions and Radial Velocities for the GAIA Era
• Galactic Tides and the Shape and Orientation of Dwarf Galaxy Satellites
• On Asymmetric Distributions of Satellite Galaxies

Cited by in corpus (2)

• Galaxy structure from multiple tracers: III. Radial variations in M87's IMF
• Two-component Jaffe models with a central black hole. I: the spherical case