On the Origin of the Monoceros Ring - I: Kinematics, proper motions, and the nature of the progenitor

Abstract

The Monoceros Ring (MRi) structure is an apparent stellar overdensity that has been postulated to entirely encircle the Galactic plane and has been variously described as being due to line-of-sight effects of the Galactic warp and flare or of extragalactic origin (via accretion). Despite being intensely scrutinised in the literature for more than a decade, no studies to-date have been able to definitively uncover its origins. Here we use $N$-body simulations and a genetic algorithm to explore the parameter space for the initial position, orbital parameters and, for the first time, the final location of a satellite progenitor. We fit our models to the latest Pan-STARRS data to determine whether an accretion scenario is capable of producing an in- Plane ring-like structure matching the known parameters of the MRi. Our simulations produce streams that closely match the location, proper motion and kinematics of the MRi structure. However, we are not able to reproduce the mass estimates from earlier studies based on Pan-STARRS data. Furthermore, in contrast with earlier studies our best-fit models are those for progenitors on retrograde orbits. If the MRi was produced by satellite accretion, we find that its progenitor has an initial mass upper limit of ~$10^{10}$M${}_{\odot }$ and the remnant is likely located behind the Galactic bulge, making it diffcult to locate observationally. While our models produce realistic MRi-like structures we cannot definitively conclude that the MRi was produced by the accretion of a satellite galaxy.

10 pages, 6 figures, 3 tables. Accepted for publication by MNRAS

References in corpus (13)

• Rings and Radial Waves in the Disk of the Milky Way
• On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution
• The Caustic Ring Model of the Milky Way Halo
• Flare in the Galactic stellar outer disc detected in SDSS-SEGUE data
• On the Origin of Dynamically Cold Rings Around the Milky Way
• Dark Matter Direct Search Rates in Simulations of the Milky Way and Sagittarius Stream
• The AAT/WFI survey of the Monoceros Ring and Canis Major Dwarf galaxy: I. from l = (193 - 276)o
• Exploring Halo Substructure with Giant Stars: The Nature of the Triangulum-Andromeda Stellar Features
• A Genetic Approach to the History of the Magellanic Clouds
• The fall of the Northern Unicorn: Tangential motions in the Galactic Anti-centre with SDSS and Gaia
• No Excess of RR Lyrae Stars in the Canis Major Overdensity
• Does the stellar distribution flare? A comparison of stellar scale heights with LAB HI data
• Does the Second Caustic Ring of Dark Matter Cause the Monoceros Ring of Stars ?

Cited by in corpus (4)

• VVVX-Gaia Discovery of a Low Luminosity Globular Cluster in the Milky Way Disk
• The outer disc in shambles: blind detection of Monoceros and ACS with Gaia's astrometric sample
• A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars
• The Chemodynamical Nature of the Triangulum-Andromeda Overdensity