Breaking up the Magellanic Group into the Milky Way Halo: Understanding the Local Dwarf Galaxy Properties

TL;DR

This study uses numerical simulations to show that the Magellanic Clouds and some dwarf spheroidals were accreted into the Milky Way from a late-infall group, explaining their properties and distribution.

Contribution

It demonstrates that the Magellanic group was tidally disrupted before entering the Milky Way, affecting the current satellite distribution and properties, offering a new formation scenario.

Findings

Half of the group satellites are within the Milky Way virial radius.

Less than 10% of the Milky Way halo mass is from the disrupted group.

20% of the brightest dwarf galaxies originated from this group.

Abstract

We use a numerical simulation of a loose group containing a Milky Way halo to probe that in the hierarchical universe the Magellanic Clouds and some dSphs have been accreted into the Milky Way halo from a late infalling group of dwarfs. Our simulations show that the tidal breakup of the Magellanic group occurs before it enters the Milky Way halo. Only half of the satellites contributed from the group are predicted to be inside the Milky Way virial radius. Half of its subhalos survive outside the current virial radius in the form of satellites, whereas the remaining material contributes to the diffuse Milky Way halo. At z~0 the disrupted group contributes less than 10% to the Milky Way halo mass but 20% of the brightest dwarf galaxies of the Milky Way have been part of this group. This scenario points out that some dSphs might have been form away from giant spirals and been accreted already as spheroids, by a late infall group in contrast with the classical picture of tidal stripping of dSph formation models. This would naturally explain several peculiarities of the local dSph: why Draco and the other luminous dSphs exist compared to other ultra-faint satellite galaxies, the location of Tucana and Cetus in the outskirts of the Local Group and the mismatch in metallicity between the stellar halo of the Milky Way and the dwarf galaxies that many have suspected dissolved to build it.