Constructing a Pristine View of Extended Globular Cluster Structure

Abstract Globular clusters (GCs) displaying extended structures are becoming increasingly ubiquitous in the Milky Way (MW). Despite their low surface brightness, which makes disentangling the true structure from the MW overwhelming difficult, the increasing availability of multidimensional data sets has allowed for new detections of extended GC structure. This work utilises the Pristine-Gaia synthetic catalog released as part of the Pristine survey’s first data release to search for tidally stripped stars in the peripheries of MW GCs. Pristine provides photometric [Fe/H] measurements based on CaHK-band photometry. Using unsupervised machine learning techniques, we provide lists of extratidal stars for 30 GCs, one of the largest surveys of its kind. We find that (1) 22 GCs that passed our quality cut have extended structure within 5 deg from the cluster centers, of which six are new tentative detections, and (2) four of those GCs exhibit diffuse-envelope-like extratidal features, while the remaining GCs exhibit tidal-tail-like structures. We measure the position angles of the extended structures, find broad consistency between the position angles and the GC orbits, and discuss our results concerning N -body models. This work demonstrates the effectiveness of adding photometric metallicities to the multidimensional search of extended tidal structure and how the upcoming multi-object spectrographs will be crucial for exploring GC peripheries in the coming years.