Signatures of minor mergers in the Milky Way disc I: The SEGUE stellar sample

TL;DR

This study detects signatures of minor mergers in the Milky Way's disc by analyzing stellar samples and N-body simulations, suggesting a Sagittarius dwarf galaxy with a dark matter halo mass below 10^{11} solar masses influenced the galaxy's structure.

Contribution

It demonstrates that phase-space features in stellar samples can be used to infer properties of past minor merger events in the Milky Way.

Findings

Similar phase-space features found in independent stellar samples.

Good model matches for Sagittarius' dark matter halo mass below 10^{11} M_sun.

Analysis can constrain Sagittarius' orbital parameters and mass.

Abstract

It is now known that minor mergers are capable of creating structure in the phase-space distribution of their host galaxy's disc. In order to search for such imprints in the Milky Way, we analyse the SEGUE F/G-dwarf and the Schuster et al. (2006) stellar samples. We find similar features in these two completely independent stellar samples, consistent with the predictions of a Milky Way minor-merger event. We next apply the same analyses to high-resolution, idealised N-body simulations of the interaction between the Sagittarius dwarf galaxy and the Milky Way. The energy distributions of stellar particle samples in small spatial regions in the host disc reveal strong variations of structure with position. We find good matches to the observations for models with a mass of Sagittarius' dark matter halo progenitor $\lessapprox 10^{11}$ M$_{\odot}$. Thus, we show that this kind of analysis could be used to provide unprecedentedly tight constraints on Sagittarius' orbital parameters, as well as place a lower limit on its mass.