A Low-Mass Stellar-Debris Stream Associated with a Globular Cluster Pair in the Halo

Abstract

There are expected to be physical relationships between the globular clusters (GCs) and stellar substructures in the Milky Way, not all of which have yet been found. We search for such substructures from a combined halo sample of SDSS blue horizontal-branch and SDSS+LAMOST RR Lyrae stars, cross-matched with astrometric information from $Gaia$ DR2. This is a sample of old stars which are also excellent tracers of structures, ideal for searching for ancient relics in the outer stellar halo. By applying the neural-network-based method StarGO to the full 4D dynamical space of our sample, we rediscover the Sagittarius Stream, and find the debris of the $Gaia$-Enceladus-Sausage (GES) and the Sequoia events in the outer halo, as well as their linkages with several GCs. Most importantly, we find a new, low-mass, debris stream associated with a pair of GCs (NGC 5024 and NGC 5053), which we dub LMS-1. This stream has a very polar orbit, and occupies a region between 10 to 20 kpc from the Galactic center. NGC 5024 (M53), the more-massive of the associated GC pair, is very likely the nuclear star cluster of a now-disrupted dwarf galaxy progenitor, based on the results from N-body simulations.

10 pages, 4 figures, accepted for ApJL

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• The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO
• Probing the Galactic Halo with RR Lyrae Stars. II. The Substructures of the Milky Way
• APOGEE spectroscopic evidence for chemical anomalies in dwarf galaxies: The case of M~54 and Sagittarius
• The Unmixed Debris of Gaia-Sausage/Enceladus in the Form of a Pair of Halo Stellar Overdensities
• The Pristine survey -- XV. A CFHT ESPaDOnS view on the Milky Way halo and disc populations
• Dynamics of Stellar Disk Tilting from Satellite Mergers
• Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster
• The SDSS-Gaia View of the Color-Magnitude Relation for Blue Horizontal-branch Stars
• RR Lyrae stars as probes of the outer Galactic halo: Chemical and kinematic analysis of a pilot sample
• Dynamical Origin for the Collinder 132-Gulliver 21 Stream: A Mixture of three Co-Moving Populations with an Age Difference of 250 Myr
• A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy
• Detection of the actinide Th in an r-process-enhanced star with accretion origin
• Discovery of the shell structure via break radii in the outer halo of the Milky Way
• A Dwarf Galaxy Debris Stream Associated with Palomar 1 and the Anticenter Stream
• The Pristine survey. XXVI. Chemical abundances of subgiant stars of the extremelymetal-poor stream C-19
• Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample
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• Identification of a dwarf galaxy stream in Gaia, and its possible association with the VPOS structure