Identification of Sagittarius stream members in Angular Momentum space with Gaussian mixture techniques

Abstract

This paper uses Gaussian mixture techniques to dissect the Milky Way (MW) stellar halo in angular momentum space. Application to a catalogue of 5389 stars near the plane of the Sagittarius (Sgr) stream with full 6D phase-space coordinates supplied by Gaia EDR3 and SEGUE returns four independent dynamical components. The broadest and most populated corresponds to the 'smooth' MW halo. The narrowest and faintest contains 40 stars of the Orphan stream. We find a component with little or no angular momentum likely associated with the GSE substructure. We also identify 925 stars and 7 Globular Clusters with probabilities > 90% to be members of the Sgr stream. Comparison against N-body models shows that some of these members trace the continuation of the leading/trailing tails in the Southern/Northern hemispheres. The new detections span ∼ 800 • on the sky, thus wrapping the Galaxy twice.

Dwarf stellar haloes: a powerful probe of small-scale galaxy formation and the nature of dark matter

“…The potential existence of satellite stellar haloes in the MW halo is an exciting prospect, and in the current and upcoming era of Gaia and wide-field spectroscopic surveys, such as DESI, WEAVE and 4MOST, this is a testable prediction. Indeed, the stellar halo of the (disrupting) Sagittarius has potentially already been uncovered by the H3 survey (Johnson et al 2020, but also see Peñarrubia & Petersen 2021). Interestingly, Johnson et al (2020) identify the diffuse halo component by selecting Sagittarius stars in angular momentum space, in excellent agreement with the outputs of our toy models.…”

The Chemo-Dynamical Groups of Galactic Globular Clusters

“…Due to recent accretion and tidal stripping, much of its material is in an easily identifiable stream. This allows 7 GCs to be identified with a high degree of certainty as being associated with the Sagittarius dwarf: Terzan7, Arp2, Terzan8, Pal12, Whiting1 and M54 (NGC6715), which is Peñarrubia & Petersen 2021). We find that these GCs have a near-certain membership.…”

“…• NGC2419 and NGC5824 are commonly linked to Sagittarius (Antoja et al 2020;Bellazzini et al 2020;Peñarrubia & Petersen 2021), but we find them almost certainly to be ungrouped. The orbit of NGC2419 is more radial than the average, more vertical Sagittarius orbit, and NGC5824 is at lower energy than the other GCs.…”

“…Arguably the easiest accreted group to identify is the set of GCs that belonged to the Sagittarius dwarf galaxy (Ibata et al 1994) as it is currently being disrupted and its stars and GCs can be found as an identifiable stream (e.g. Bellazzini et al 2020;Antoja et al 2020;Law & Majewski 2010;Peñarrubia & Petersen 2021). Identifying members of other stellar halo structures remains a challenging problem.…”