A possible impact near the Milky Way of a former major merger in the Local Group

TL;DR

This paper proposes that the Milky Way's dwarf system, including the Magellanic Clouds, may have originated from tidal debris of a past major merger involving Andromeda, explaining their distribution and proximity.

Contribution

It introduces a novel scenario where MW dwarves formed in a tidal tail from a historic merger, accounting for their distribution and proximity to the MW.

Findings

Reproduces the Vast Polar Structure (VPOS) of MW dwarves.

Explains the proximity of Magellanic Clouds to MW.

Predicts dark-matter free dwarves, challenging current understanding.

Abstract

The Milky Way (MW) dwarf system presents two exceptional features, namely it forms a thick plane called the Vast Polar Structure (VPOS), and the two biggest dwarves, the Magellanic Clouds (MCs), are irregular galaxies that are almost never seen at such a proximity from a luminous, L* galaxy. Investigating from our modelling of M31 as a result of a former gas-rich major merger, we find that one of the expected tidal tail produced during the event may have reached the MW. Such a coincidence may appear quite exceptional, but the MW indeed lies within the small volume delineated by the tidal tail at the present epoch. In our scenario, most of the MW dwarves, including the MCs, may have been formed within a tidal tail formed during the former merger in the Local Group. It leads to a fair reproduction of the VPOS as well as to a simple explanation of the MCs proximity to the MW, i.e. accounting for both exceptional features of the MW dwarf distributions. However this scenario predicts dark-matter free MW dwarves, which is in apparent contradiction with their intrinsically large velocity dispersions. To be established or discarded, this requires to further investigate their detailed interactions with the MW potential.