Searching for the extra-tidal stars of globular clusters using high-dimensional analysis and a core particle spray code

TL;DR

This paper introduces a novel high-dimensional data analysis approach combined with a particle spray simulation to identify and confirm extra-tidal stars of globular clusters, exemplified by M3, enhancing understanding of cluster dynamics.

Contribution

The study develops a new methodology integrating machine learning dimensionality reduction and a three-body particle spray code to detect and verify extra-tidal stars of globular clusters.

Findings

Identified 103 candidate extra-tidal stars using t-SNE and UMAP.

Confirmed 10 high-probability extra-tidal stars associated with M3.

Demonstrated the effectiveness of corespray in modeling star ejections.

Abstract

Three-body interactions can eject stars from the core of a globular cluster, causing them to enter the Galactic halo as extra-tidal stars. While finding extra-tidal stars is imperative for understanding cluster evolution, connecting isolated extra-tidal field stars back to their birth cluster is extremely difficult. In this work, we present a new methodology consisting of high-dimensional data analysis and a particle spray code to identify extra-tidal stars of any Galactic globular cluster using M3 as a case study. Using the t-Stochastic Neighbour Embedding (t-SNE) and Uniform Manifold Approximation and Projection (UMAP) machine learning dimensionality reduction algorithms, we first identify a set of 103 extra-tidal candidates in the APOGEE DR17 data catalogue with chemical abundances similar to M3 stars. To confirm each candidate's extra-tidal nature, we introduce corespray - a new Python-based three-body particle spray code that simulates extra-tidal stars for any Galactic globular cluster. Using Gaia EDR3 proper motions and APOGEE DR17 radial velocities, we apply multivariate Gaussian modelling and an extreme deconvolution to identify the extra-tidal candidates that are more likely to be associated with a distribution of corespray-simulated M3 extra-tidal stars than the field. Through these methods, we identify 10 new high-probability extra-tidal stars produced via three-body interactions in M3. We also explore whether any of our extra-tidal candidates are consistent with being ejected from M3 through different dynamical processes. Future applications of corespray will yield better understandings of core dynamics, star formation histories and binary fractions in globular clusters.