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Title: Tracing chemical evolution over the extent of the Milky Way's disk with apogee red clump stars

We employ the first two years of data from the near-infrared, high-resolution SDSS-III/APOGEE spectroscopic survey to investigate the distribution of metallicity and α-element abundances of stars over a large part of the Milky Way disk. Using a sample of ≈10, 000 kinematically unbiased red-clump stars with ∼5% distance accuracy as tracers, the [α/Fe] versus [Fe/H] distribution of this sample exhibits a bimodality in [α/Fe] at intermediate metallicities, –0.9 < [Fe/H] <–0.2, but at higher metallicities ([Fe/H] ∼+0.2) the two sequences smoothly merge. We investigate the effects of the APOGEE selection function and volume filling fraction and find that these have little qualitative impact on the α-element abundance patterns. The described abundance pattern is found throughout the range 5 < R < 11 kpc and 0 < |Z| < 2 kpc across the Galaxy. The [α/Fe] trend of the high-α sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (∼10%). Using simple galactic chemical evolution models, we derive an average star-formation efficiency (SFE) in the high-α sequence of ∼4.5 × 10{sup –10} yr{sup –1}, which is quite close to the nearly constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the earlymore » evolution of the Milky Way disk was characterized by stars that shared a similar star-formation history and were formed in a well-mixed, turbulent, and molecular-dominated ISM with a gas consumption timescale (SFE{sup –1}) of ∼2 Gyr. Finally, while the two α-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track, this cannot hold in the outer Galaxy, requiring, instead, a mix of two or more populations with distinct enrichment histories.« less
 [1] ;  [2] ;  [3] ; ; ;  [4] ; ; ;  [5] ; ;  [6] ;  [7] ; ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ;  [13] ;  [14] more »; « less
  1. Department of Astronomy, University of Michigan, Ann Arbor, MI 48104 (United States)
  2. Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)
  3. Physics and Astronomy Department, Vanderbilt University, 1807 Station B, Nashville, TN 37235 (United States)
  4. Department of Astronomy and the Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States)
  5. New Mexico State University, Las Cruces, NM 88003 (United States)
  6. Department of Astronomy, University of Virginia, Charlottesville, VA, 22904 (United States)
  7. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
  8. Institut Utinam, CNRS UMR 6213, OSU THETA, Université de Franche-Comté, 41bis avenue de l'Observatoire, F-25000 Besançon (France)
  9. Observatorio Nacional, Rio de Janeiro (Brazil)
  10. Instituto de Astrofsica de Canarias, E-38205 La Laguna, Tenerife (Spain)
  11. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
  12. Astrophysics Research Institute, IC2, Liverpool Science Park, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF (United Kingdom)
  13. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  14. University of Texas at Austin, McDonald Observatory, 32 Fowlkes Road, McDonald Observatory, TX 79734-3005 (United States)
Publication Date:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 796; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States