Imprints of radial migration on the Milky Way’s metallicity distribution functions

Loebman, Sarah R., Debattista, Victor P orcid iconORCID: 0000-0001-7902-0116, Nidever, David L., Hayden, Michael R., Holtzman, Jon A., Clarke, Adam J., Roškar, Rok and Valluri, Monica (2016) Imprints of radial migration on the Milky Way’s metallicity distribution functions. The Astrophysical Journal Letters, 818 (1). L6. ISSN 2041-8213

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Recent analysis of the SDSS-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 12 stellar catalog has revealed that the Milky Way’s (MW) metallicity distribution function (MDF) changes shape as a function of radius, transitioning from being negatively skewed at small Galactocentric radii to positively skewed at large Galactocentric radii. Using a high-resolution, N-body+SPH simulation, we show that the changing skewness arises from radial migration—metal-rich stars form in the inner disk and subsequently migrate to the metal-poorer outer disk. These migrated stars represent a large fraction (>50%) of the stars in the outer disk; they populate the high-metallicity tail of the MDFs and are, in general, more metal-rich than the surrounding outer disk gas. The simulation also reproduces another surprising APOGEE result: the spatially invariant high-[α/Fe] MDFs. This arises in the simulation from the migration of a population formed within a narrow range of radii (3.2 ±1.2 kpc) and time (8.8 ± 0.6 Gyr ago), rather than from spatially extended star formation in a homogeneous medium at early times. These results point toward the crucial role radial migration has played in shaping our MW.

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