On the identification of merger debris in the {\it Gaia} Era

TL;DR

This study models the Galactic stellar halo formation through satellite accretion, creating a Gaia-like catalogue to analyze substructure, and demonstrates the potential to identify and date accretion events despite observational errors.

Contribution

It introduces a method to detect and date accreted satellite debris in the Gaia era using phase-space clustering and frequency analysis.

Findings

Successfully isolates about 50% of satellite debris in simulated Gaia data.

Accurately estimates accretion times for roughly 30% of satellites.

Phase-space substructure remains detectable despite observational errors.

Abstract

We model the formation of the Galactic stellar halo via the accretion of satellite galaxies onto a time-dependent semi-cosmological galactic potential. Our goal is to characterize the substructure left by these accretion events in a close manner to what may be possible with the {\it Gaia} mission. We have created a synthetic {\it Gaia} Solar Neighbourhood catalogue by convolving the 6D phase-space coordinates of stellar particles from our disrupted satellites with the latest estimates of the {\it Gaia} measurement errors, and included realistic background contamination due to the Galactic disc(s) and bulge. We find that, even after accounting for the expected observational errors, the resulting phase-space is full of substructure. We are able to successfully isolate roughly 50% of the different satellites contributing to the `Solar Neighbourhood' by applying the Mean-Shift clustering algorithm in energy-angular momentum space. Furthermore, a Fourier analysis of the space of orbital frequencies allows us to obtain accurate estimates of time since accretion for approximately 30% of the recovered satellites.