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A Disk Origin for the Monoceros Ring and A13 Stellar Overdensities

MPS-Authors

Sheffield,  Allyson A.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Price-Whelan,  Adrian M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Tzanidakis,  Anastasios
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Johnston,  Kathryn V.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Laporte,  Chervin F. P.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Sesar,  Branimir
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

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Citation

Sheffield, A. A., Price-Whelan, A. M., Tzanidakis, A., Johnston, K. V., Laporte, C. F. P., & Sesar, B. (2018). A Disk Origin for the Monoceros Ring and A13 Stellar Overdensities. The Astrophysical Journal, 854.


Cite as: https://hdl.handle.net/21.11116/0000-0005-CB1A-A
Abstract
The Monoceros Ring (also known as the Galactic Anticenter Stellar Structure) and A13 are stellar overdensities at estimated heliocentric distances of d ̃ 11 kpc and 15 kpc observed at low Galactic latitudes toward the anticenter of our Galaxy. While these overdensities were initially thought to be remnants of a tidally disrupted satellite galaxy, an alternate scenario is that they are composed of stars from the Milky Way (MW) disk kicked out to their current location due to interactions between a satellite galaxy and the disk. To test this scenario, we study the stellar populations of the Monoceros Ring and A13 by measuring the number of RR Lyrae and M giant stars associated with these overdensities. We obtain low-resolution spectroscopy for RR Lyrae stars in the two structures and measure radial velocities to compare with previously measured velocities for M giant stars in the regions of the Monoceros Ring and A13, to assess the fraction of RR Lyrae to M giant stars (f RR:MG) in A13 and Mon/GASS. We perform velocity modeling on 153 RR Lyrae stars (116 in the Monoceros Ring and 37 in A13) and find that both structures have very low f RR:MG. The results support a scenario in which stars in A13 and Mon/GASS formed in the MW disk. We discuss a possible association between Mon/GASS, A13, and the Triangulum-Andromeda overdensity based on their similar velocity distributions and f RR:MG.