TRACING CHEMICAL EVOLUTION OVER THE EXTENT OF THE MILKY WAY'S DISK WITH APOGEE RED CLUMP STARS

By D. Nidever, Jo Bovy, J. Bird, B. Andrews, M. Hayden, J. Holtzman, S. Majewski, V. Smith, Annie Robin, A. G. Pérez and 33 more. 2014

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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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c37eec24f8e1524dc679321a4ba11f4be85255d6

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Citations in the corpus

THE ELEVENTH AND TWELFTH DATA RELEASES OF THE SLOAN DIGITAL SKY SURVEY: FINAL DATA FROM SDSS-III (2015, methodology): “…DR11 data have been used in several papers, including a determination of distances to and chemical abundances of red-clump stars (Bovy et al. 2014; Nidever et al. 2014), mapping of the Galactic interstellar medium SDSS DR12 11 using diffuse interstellar bands measured along the line of sight to…”
The structure and dynamical evolution of the stellar disc of a simulated Milky Way-mass galaxy (2016, background): “Also, our simulation does not show any bimodality in the [α/Fe]– [M/H] relation, in contrast to some observations of MW stars (e.g. Nidever et al. 2014).”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, methodology): “Indeed, the α-rich thick disk is centrally concentrated with a short scale length of about 2 kpc (Bensby et al. 2011; Bovy et al. 2012, 2016; Cheng et al. 2012b), and very few α-rich stars are found in the outer disk of the Milky Way (Nidever et al. 2014; Hayden et al. 2015).”
StarHorse : a Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars (2017, methodology): “…for mapping the chemical and kinematical properties of Galactic populations using large stellar surveys (e.g., Boeche et al. 2013, 2014; Anders et al. 2014; Recio-Blanco et al. 2014; Nidever et al. 2014; Mikolaitis et al. 2014; Hayden et al. 2015; Carlin et al. 2015; Bovy et al. 2016).”
Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, methodology): “Chemically, it is thought to be distinct from the thin disk component in the [α/Fe]metallicity plane with a high [α/Fe] signature (e.g. Bensby, Feltzing & Oey 2014; Nidever et al. 2014; Recio-Blanco et al. 2014).”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, result): “Recent studies show that the earlier counter claims likely suffered from underestimating measurement errors (e.g., Nidever et al. 2014) or they incorrectly assumed that errors between measurements are uncorrelated (e.g., Schönrich et al. 2014).”
Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s) (2017, unknown): “15 in Nidever et al. 2014).”
Constraining the Milky Way assembly history with Galactic Archaeology (2016, methodology): “…long time in high-resolution spectroscopic data in the solar vicinity (e.g., Adibekyan et al. 2013; Bensby et al. 2013; Fuhrmann 2004) Copyright line will be provided by the publisher and more recently found in a range of Galactic radii using APOGEE data (Anders et al., 2014; Nidever et al., 2014).”
CHEMICAL CARTOGRAPHY WITH APOGEE: METALLICITY DISTRIBUTION FUNCTIONS AND THE CHEMICAL STRUCTURE OF THE MILKY WAY DISK (2015, methodology): “Meanwhile, Nidever et al. (2014) found that the position of the locus of low-[α/Fe] (thin-disk) stars depends on location within the Galaxy (see also Edvardsson et al. 1993), and it is possible that in the inner Galaxy the high- and low-[α/Fe] populations are connected, rather than distinct.”
Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances (2014, background): “The APOGEE survey (see Anders et al. 2014; Nidever et al. 2014) has shown that stars with [Fe/H]>+0.2 dex and [Fe/H]< −0.2 dex are present at just R<7 kpc and R>9kpc respectively, which explains why simple blurring can bring these stars to the solar orbit.”
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient (2016, background): “This indicates that the chemical properties of the thick disc population is radially well mixed (see also Bensby et al. 2011; Nidever et al. 2014), while the thin disc population preserves their radial and vertical metallicity gradient well.”
The age–metallicity structure of the Milky Way disc using APOGEE (2017, methodology): “These scenarios are also discussed in the context of the APOGEE results by Nidever et al. (2014).”
THE STELLAR POPULATION STRUCTURE OF THE GALACTIC DISK (2015, background): “…Bergemann et al. 2014; Martig et al. 2015), this implies that similar physical conditions existed throughout the disk at early times, a conclusion also reached 18 by Nidever et al. (2014), because of the constant locus of the high-[α/Fe] sequence in the ([Fe/H], [α/Fe]) plane throughout the disk.”
The biggest splash (2019, background): “For example, this is the highest metallicity where the bimodality in [α/Fe] can be established (see e.g. Nidever et al. 2014).”