Journal
ASTROPHYSICAL JOURNAL
Volume 808, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/808/2/132
Keywords
Galaxy: abundances; Galaxy: disk; Galaxy: evolution; Galaxy: stellar content; Galaxy: structure
Categories
Funding
- NSF [AST-1109718, AST-1211853]
- John N. Bahcall Fellowship
- W.M. Keck Foundation
- McLaughlin Fellowship at the University of Michigan
- Vanderbilt Office of the Provost through Vanderbilt Initiative in Data-intensive Astrophysics (VIDA)
- Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) [PHY 08-22648]
- Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE) [PHY 1430152]
- US National Science Foundation
- Spanish Ministry of Economy and Competitiveness [AYA-2011-27754]
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy Office of Science
- University of Arizona
- Brazilian Participation Group
- Brookhaven National Laboratory
- Carnegie Mellon University
- University of Florida
- French Participation Group
- German Participation Group
- Harvard University
- Instituto de Astrofisica de Canarias
- Michigan State/Notre Dame/JINA Participation Group
- Johns Hopkins University
- Lawrence Berkeley National Laboratory
- Max Planck Institute for Astrophysics
- Max Planck Institute for Extraterrestrial Physics
- New Mexico State University
- New York University
- Ohio State University
- Pennsylvania State University
- University of Portsmouth
- Princeton University
- Spanish Participation Group
- University of Tokyo
- University of Utah
- Vanderbilt University
- University of Virginia
- University of Washington
- Yale University
- Science and Technology Facilities Council [ST/M000966/1] Funding Source: researchfish
- Direct For Mathematical & Physical Scien [1109178] Funding Source: National Science Foundation
- Division Of Astronomical Sciences [1211853, 1109888] Funding Source: National Science Foundation
- Division Of Physics [1430152] Funding Source: National Science Foundation
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Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [alpha/Fe] versus [Fe/H] plane and the metallicity distribution functions (MDFs) across an unprecedented volume of the Milky Way disk, with radius 3 < R < 15 kpc and height vertical bar vertical bar < 2 kpc. Stars in the inner disk (R < 5 kpc) lie along a single track in [alpha/Fe] versus [Fe/H], starting with alpha-enhanced, metal-poor stars and ending at [alpha/Fe] similar to 0 and [Fe/H] similar to + 0.4. At larger radii we find two distinct sequences in [alpha/Fe] versus [Fe/H] space, with a roughly solar-alpha sequence that spans a decade in metallicity and a high-alpha sequence that merges with the low-alpha sequence at super-solar [Fe/H]. The location of the high-alpha sequence is nearly constant across the disk;. however, there are very few high-alpha stars at R > 11 kpc. The peak of the midplane MDF shifts to lower metallicity at larger R, reflecting the Galactic metallicity gradient. Most strikingly, the shape of the midplane MDF changes systematically with radius, from a negatively skewed distribution at 3 < R < 7 kpc, to a roughly Gaussian distribution at the solar annulus, to a positively skewed shape in the outer Galaxy. For stars with vertical bar z vertical bar > 1 kpc or [alpha/Fe] > 0.18, the MDF shows little dependence on R. 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.
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