A Disk Origin for the Monoceros Ring and A13 Stellar Overdensities

作者：Sheffield Allyson A; Price Whelan Adrian M; Tzanidakis Anastasios; Johnston Kathryn V; Laporte Chervin F P; Sesar Branimir

来源：Astrophysical Journal, 2018, 854(1): 47.

DOI：10.3847/1538-4357/aaa4b6

<jats:title>Abstract</jats:title>
<jats:p>The Monoceros Ring (also known as the Galactic Anticenter Stellar Structure) and A13 are stellar overdensities at estimated heliocentric distances of <jats:italic>d</jats:italic> ∼ 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 (<jats:italic>f</jats:italic>
<jats:sub>RR:MG</jats:sub>) 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 <jats:italic>f</jats:italic>
<jats:sub>RR:MG</jats:sub>. 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 <jats:italic>f</jats:italic>
<jats:sub>RR:MG</jats:sub>.</jats:p>

• 出版日期2018-2-10