Disrupted dwarf binary merger as the possible origin of NGC 2419 and Sagittarius stream substructure

TL;DR

This study uses N-body simulations to propose that dwarf galaxy mergers can explain the large separations and complex structures observed in the Sagittarius stream and NGC 2419, suggesting a new origin scenario.

Contribution

It introduces a novel double merger model for dwarf galaxies that accounts for observed substructures and separations in the Sagittarius stream and NGC 2419.

Findings

Simulations reproduce large separations of bound particles post-merger.

The model explains complex tidal features like clouds and bifurcations.

Supports the idea that NGC 2419 is a nuclear star cluster.

Abstract

Using $N$-body simulations, we demonstrate that satellite dwarf galaxy pairs which undergo significant mixing ($\sim 6$ Gyr) can have their respective most bound particles separated great distances upon subsequently merging with a more massive host. This may provide an explanation as to the origin of the complex globular cluster NGC 2149, which is found within the tail of the Sagittarius dwarf spheroidal galaxy, yet separated from its central remnant by over 100 kpc. Dynamical investigations could support the chemical evidence which already points to the NGC 2419 being a nuclear star cluster. Motivated by the distinct nature of NGC 2419, we run a suite of simulations whereby an initial pre-infall merger of two satellites is followed by a post-infall merger of the remnant into a MW-like host potential. We present a striking example from our suite in this work, in which this separation is reproduced by the most bound particles of the two pre-infall satellites. Additionally, this double merger scenario can induce unusual on-sky features in the tidal debris of the post-infall merger, such as clouds, overdensities, and potentially new arms that could resemble the bifurcation observed in Sagittarius.