The Chemodynamical Nature of the Triangulum–Andromeda Overdensity

Abstract

We present a chemodynamical study of the Triangulum–Andromeda overdensity (TriAnd) employing a sample of 31 candidate stars observed with the GRACES high-resolution ( R = 40,000) spectrograph at the Gemini North (8.1 m) telescope. TriAnd is a stellar substructure found toward the outer disk of the Milky Way, located at R _GC ∼ 18 kpc from the Sun, toward Galactic latitude b ∼ 25°. Most stars in our sample have dynamical properties compatible with a disk stellar population. In addition, by applying an eccentricity cut, we are able to detect a stellar contamination that seems to be consistent with an accreted population. In chemical abundance space, the majority of our TriAnd candidates are similar to the outer thin-disk population, suggesting that the overdensity has an in situ origin. Finally, the found accreted halo interlopers spatially overlapping with TriAnd should explain the historical discussion of the overdensity’s nature due to its complex chemical patterns.

Keywords

• Chemical abundances
• Milky Way disk
• Galaxy kinematics
• Milky Way stellar halo
• High resolution spectroscopy
• Galactic archaeology