paper

Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk

arXiv:1503.02110 · doi:10.1088/0004-637X/808/2/132

Abstract

Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [/Fe] vs. [Fe/H] plane and the metallicity distribution functions (MDF) across an unprecedented volume of the Milky Way disk, with radius kpc and height kpc. Stars in the inner disk ( kpc) lie along a single track in [/Fe] vs. [Fe/H], starting with -enhanced, metal-poor stars and ending at [/Fe] and [Fe/H]. At larger radii we find two distinct sequences in [/Fe] vs. [Fe/H] space, with a roughly solar- sequence that spans a decade in metallicity and a high- sequence that merges with the low- sequence at super-solar [Fe/H]. The location of the high- sequence is nearly constant across the disk, however there are very few high- stars at kpc. The peak of the midplane MDF shifts to lower metallicity at larger , reflecting the Galactic metallicity gradient. Most strikingly, the shape of the midplane MDF changes systematically with radius, with a negatively skewed distribution at kpc, to a roughly Gaussian distribution at the solar annulus, to a positively skewed shape in the outer Galaxy. For stars with kpc or [/Fe], the MDF shows little dependence on . The positive skewness of the outer disk MDF may be a signature of radial migration; we show that blurring of stellar populations by orbital eccentricities is not enough to explain the reversal of MDF shape but a simple model of radial migration can do so.

Submitted, 18 pages, 16 figures

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