Leo IV & V - A possible dwarf galaxy pair ?

TL;DR

This study investigates whether the faint dwarf galaxies Leo IV and Leo V form a gravitationally bound pair by modeling their dark matter halos, suggesting it is plausible given their dark matter content.

Contribution

The paper introduces a simple integration and N-body simulation approach to assess the bound status of the Leo IV and V dwarf galaxy pair considering dark matter halos.

Findings

A high dark matter mass is needed for the pair to be bound.

Models are consistent with predicted dark matter content for faint satellites.

It is plausible that Leo IV and V form a bound galaxy pair.

Abstract

The last few years have seen the discovery of many faint and ultra-faint dwarf spheroidal galaxies around the Milky Way. Among these is a pair of satellites called Leo IV and Leo V. This pair is found at large distances from the Milky Way (154 and 175 kpc respectively). The rather small difference in radial distance, and the fact that they also show a close projected distance on the sky, has led to the idea that we might be seeing a new pair of bound galaxies - like the Magellanic Clouds. In this paper we investigate this speculation by means of a simple integration code (confirming the results with full N-body simulations). As the luminous mass of both faint dwarfs is far too low to allow them to be bound, we simulate the pair assuming extended dark matter haloes. Our results show that the minimum dark matter mass required for the pair to be bound is rather high - ranging from 1.6 x 10^10 Msun to 5.4 x 10^10 Msun (within the virial radii). Computing the mass of dark matter within a commonly adopted radius of 300 pc shows that our models are well within the predicted range of dark matter content for satellites so faint. We therefore conclude that it could be possible that the two galaxies constitute a bound pair.