Identifying Local Group Field Galaxies which have interacted with the Milky Way

TL;DR

This study uses simulations and observations to identify which Local Group field galaxies have likely interacted with the Milky Way, revealing that about 13% of galaxies in a certain distance range are escapees with signs of past interactions.

Contribution

It introduces a statistical method combining simulations and observational data to identify Local Group galaxies that have interacted with the Milky Way, highlighting their properties and evolutionary signatures.

Findings

Approximately 13% of galaxies between 300-1500 kpc are Milky Way escapees.

Identified galaxies show signs of past interactions in morphology, star formation, and gas content.

Several known galaxies are likely to have passed through the Milky Way's virial volume.

Abstract

We distinguish between Local Group field galaxies which may have passed through the virial volume of the Milky Way, and those which have not, via a statistical compari- son against populations of dark matter haloes in the Via Lactea II (VLII) simulation with known orbital histories. Analysis of VLII provides expectations for this escaped population: they contribute 13 per cent of the galactic population between 300 and 1500 kpc from the Milky Way, and hence we anticipate that about 7 of the 54 known Local Group galaxies in that distance range are likely to be Milky Way escapees. These objects can be of any mass below that of the Milky Way, and they are expected to have positive radial velocities with respect to the Milky Way. Comparison of the radius-velocity distributions of VLII populations and measurements of Local Group galaxies presents a strong likelihood that Tucana, Cetus, NGC3109, SextansA, SextansB, Antlia, NGC6822, Phoenix, LeoT, and NGC185 have passed through the Milky Way. Most of these dwarfs have a lower HI mass fraction than the majority of dwarfs lying at similar distances to either the Milky Way or M31. Indeed, several of these galaxies - especially those with lower masses - contain signatures in their morphology, star formation history and/or gas content indicative of evolution seen in simulations of satellite/parent galactic interactions. Our results offer strong support for scenarios in which dwarfs of different types form a sequence in morphology and gas content, with evolution along the sequence being driven by interaction history.