Tracing Chemical Evolution Over The Extent Of The Milky Way's Disk With Apogee Red Clump Stars
David L. Nidever
(1)
,
Jo Bovy
(2)
,
Jonathan C. Bird
(3)
,
Brett H. Andrews
(4)
,
Michael Hayden
(5)
,
Jon Holtzman
(5)
,
Steven R. Majewski
(6)
,
Verne Smith
(7)
,
Annie C. Robin
(8)
,
Ana E. García Pérez
(6)
,
Katia Cunha
(9, 10)
,
Carlos Allende Prieto
(11, 12)
,
Gail Zasowski
(13)
,
Ricardo P. Schiavon
(14)
,
Jennifer A. Johnson
(4)
,
David H. Weinberg
(4)
,
Diane Feuillet
(5)
,
Donald P. Schneider
(15)
,
Matthew Shetrone
(16)
,
Jennifer Sobeck
(8)
,
D. A. García-Hernández
(11, 12)
,
O. Zamora
(11, 12)
,
Hans-Walter Rix
(17)
,
Timothy C. Beers
(18)
,
John C. Wilson
(6)
,
Robert W. O'Connell
(6)
,
Ivan Minchev
(19)
,
Cristina Chiappini
(19)
,
Friedrich Anders
(19)
,
Dmitry Bizyaev
(5)
,
Howard Brewington
(5)
,
Garrett Ebelke
(5)
,
Peter M. Frinchaboy
(20)
,
Jian Ge
(21)
,
Karen Kinemuchi
(5)
,
Elena Malanushenko
(5)
,
Viktor Malanushenko
(5)
,
Moses Marchante
(5)
,
Szabolcs Mészáros
(22, 23)
,
Daniel Oravetz
(5)
,
Kaike Pan
(5)
,
Audrey Simmons
(5)
,
Michael F. Skrutskie
(6)
1
University of Michigan [Ann Arbor]
2 IAS - Institute for Advanced Study [Princeton]
3 Vanderbilt University [Nashville]
4 OSU - Ohio State University [Columbus]
5 New Mexico State University
6 University of Virginia
7 NOAO - National Optical Astronomy Observatory
8 UTINAM - Univers, Théorie, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
9 Observatorio Nacional [Rio de Janeiro]
10 Steward Observatory
11 IAC - Instituto de Astrofisica de Canarias
12 ULL - Universidad de La Laguna [Tenerife - SP]
13 JHU - Johns Hopkins University
14 ARI - Astrophysics Research Institute [Liverpool]
15 Penn State - Pennsylvania State University
16 University of Texas at Austin [Austin]
17 MPIA - Max-Planck-Institut für Astronomie
18 UND - University of Notre Dame [Indiana]
19 AIP - Leibniz-Institut für Astrophysik Potsdam
20 TCU - Texas Christian University
21 UF - University of Florida [Gainesville]
22 Indiana University [Bloomington]
23 ELTE - Eötvös Loránd University
2 IAS - Institute for Advanced Study [Princeton]
3 Vanderbilt University [Nashville]
4 OSU - Ohio State University [Columbus]
5 New Mexico State University
6 University of Virginia
7 NOAO - National Optical Astronomy Observatory
8 UTINAM - Univers, Théorie, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
9 Observatorio Nacional [Rio de Janeiro]
10 Steward Observatory
11 IAC - Instituto de Astrofisica de Canarias
12 ULL - Universidad de La Laguna [Tenerife - SP]
13 JHU - Johns Hopkins University
14 ARI - Astrophysics Research Institute [Liverpool]
15 Penn State - Pennsylvania State University
16 University of Texas at Austin [Austin]
17 MPIA - Max-Planck-Institut für Astronomie
18 UND - University of Notre Dame [Indiana]
19 AIP - Leibniz-Institut für Astrophysik Potsdam
20 TCU - Texas Christian University
21 UF - University of Florida [Gainesville]
22 Indiana University [Bloomington]
23 ELTE - Eötvös Loránd University
Résumé
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 × 10−10 yr−1, which is quite close to the nearly constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the early 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−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.