Detecting globular cluster tidal extensions with Bayesian inference – I. Analysis of ω Centauri with Gaia EDR3

Abstract

The peripheral regions of globular clusters (GCs) are extremely challenging to study due to their low surface brightness nature and the dominance of Milky Way contaminant populations along their sightlines. We have developed a probabilistic approach to this problem through utilising a mixture model in spatial and proper motion space which separately models the cluster, extra-tidal and contaminant stellar populations. We demonstrate the efficacy of our method through application to Gaia EDR3 photometry and astrometry in the direction of NGC 5139 (ω Cen), a highly challenging target on account of its Galactic latitude (b ≈ 15○) and low proper motion contrast with the surrounding field. We recover the spectacular tidal extensions, spanning the 10○ on the sky explored here, seen in earlier work and quantify the star count profile and ellipticity of the system out to a cluster-centric radius of 4○. We show that both RR Lyrae and blue horizontal branch stars consistent with belonging to ω Cen are found in the tidal tails, and calculate that these extensions contain at least ≈0.1 per cent of the total stellar mass in the system. Our high probability members provide prime targets for future spectroscopic studies of ω Cen out to unprecedented radii.

A search for stellar structures around nine outer halo globular clusters in the Milky Way

“…PCB20 classify it as 'T' based on the detection of long tidal tails using Gaia DR2 by Ibata et al (2019a,b) -the socalled Fimbulthul stream. This detection is reinforced by Ibata et al (2021); the tails are also easily detectable in the region immediately surrounding the cluster, as shown by Sollima (2020) and Kuzma et al (2021). We classify this cluster as 'T'.…”

“…As with many problems in near-field astrophysics, the availability of Gaia astrometry has led to a slew of new discoveries in this area of research, with many globular clusters now known to possess long (but generally extremely faint) tidal tails (e.g., Carballo-Bello 2019;Carballo-Bello et al 2020;Kaderali et al 2019;Sollima 2020;Ibata et al 2019bIbata et al ,a, 2021Palau & Miralda-Escudé 2021;Bonaca et al 2021;Kuzma et al 2021). However, Gaia studies are typically limited to relatively nearby clusters such that traditional groundbased wide-field imaging surveys are still useful for exploring more distant systems.…”

Rubin Observatory LSST Stars Milky Way and Local Volume Star Clusters Roadmap

“…In contrast, LSST will be homogeneous and deeper. For inner halo GCs, Gaia has allowed detailed explorations of GC outskirts (e.g., de Boer et al 2019;Sollima 2020;Kuzma et al 2021). Indeed, as illustrated and quantified by Cantat-Gaudin et al (2023), the Gaia catalogs become severely incomplete in the central parts of globular clusters.…”

Forward and back: kinematics of the Palomar 5 tidal tails

“…Thanks to large, wellcalibrated imaging surv e ys such as Sloan Digital Sky Survey (SDSS; Ahn et al 2012 ) and Pan-STARRS1 (PS1; Chambers et al 2016 ), as well as the more recent astrometric Gaia space mission (Gaia Collaboration et al 2018 ), tidal features have been found around a few tens of GCs in the MW halo (e.g. Sollima 2020 ; Kuzma et al, in preparation), ranging from the massive inner halo NGC 5139 (Ibata et al 2019 ;Kuzma, Ferguson & Pe ˜ narrubia 2021 ) to the lowmass outer halo Palomar 1 (Niederste-Ostholt et al 2010 ). The most emphatic display of tidal features in the MW, ho we ver, belongs to Palomar 5 (Pal 5; Odenkirchen et al 2001Odenkirchen et al , 2003.…”