Discovery of new globular clusters in the Sagittarius dwarf galaxy

Abstract

Context. Globular clusters (GCs) are witnesses of the past accretion events onto the Milky Way (MW). In particular, the GCs of the Sagittarius (Sgr) dwarf galaxy are important probes of an on-going merger. Aims. Our main goal is to search for new GC members of this dwarf galaxy using the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-infrared database combined with the Gaia Early Data Release 3 (EDR3) optical database. Methods. We investigated all VVVX-enabled discoveries of GC candidates in a region covering about 180 sq. deg. toward the bulge and the Sgr dwarf galaxy. We used multiband point-spread function photometry to obtain deep color-magnitude diagrams (CMDs) and luminosity functions (LFs) for all GC candidates, complemented by accurate Gaia-EDR3 proper motions (PMs) to select Sgr members and variability information to select RR Lyrae which are potential GC members. Results. After applying a strict PM cut to discard foreground bulge and disk stars, the CMDs and LFs for some of the GC candidates exhibit well defined red giant branches and red clump giant star peaks. We selected the best Sgr GCs, estimating their distances, reddenings, and associated RR Lyrae. Conclusions. We discover 12 new Sgr GC members, more than doubling the number of GCs known in this dwarf galaxy. In addition, there are 11 other GC candidates identified that are uncertain, awaiting better data for confirmation.

Kinematics beats dust: unveiling nested substructure in the perturbed outer disc of the Milky Way

“…At face value this suggests that an extended thin disc might have already been in place at z ∼ 2 (Laporte et al 2020). Reproducing the physical extent of havoc in the outer disc requires invoking a larger progenitor halo masses for Sgr than historically assumed (M halo ≥ 6×10 10 M see Gibbons et al 2017;Laporte et al 2018) which is further supported by the recent discovery of a large number of globular clusters (GC) associated with Sgr (Minniti et al 2021) increasing the specific frequency of GCs, hence progenitor halo mass (e.g. Hudson et al 2014).…”