The age–metallicity structure of the Milky Way disc using APOGEE

By J. Mackereth, Jo Bovy, R. Schiavon, G. Zasowski, K. Cunha, P. Frinchaboy, A. G. Pérez, M. Hayden, J. Holtzman, S. Majewski and 4 more. 2017

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The measurement of the structure of stellar populations in the Milky Way disc places fundamental constraints on models of galaxy formation and evolution. Previously, the disc’s structure has been studied in terms of populations defined geometrically and/or chemically, but a decomposition based on stellar ages provides a more direct connection to the history of the disc, and stronger constraint on theory. Here, we use positions, abundances and ages for 31 244 red giant branch stars from the Sloan Digital Sky Survey (SDSS)-APOGEE survey, spanning 3 < Rgc < 15 kpc, to dissect the disc into mono-age and mono-[Fe/H] populations at low and high [α/Fe]. For each population, with age < 2 Gyr and [Fe/H] < 0.1 dex, we measure the structure and surface-mass density contribution. We find that low [α/Fe] mono-age populations are fit well by a broken exponential, which increases to a peak radius and decreases thereafter. We show that this profile becomes broader with age, interpreted here as a new signal of disc heating and radial migration. High [α/Fe] populations are well fit as single exponentials within the radial range considered, with an average scalelength of 1.9 ± 0.1 kpc. We find that the relative contribution of high to low [α/Fe] populations at R0 is f� = 18 per cent ± 5 per cent; high [α/Fe] contributes most of the mass at old ages, and low [α/Fe] at young ages. The low and high [α/Fe] populations overlap in age at intermediate [Fe/H], although both contribute mass at R0 across the full range of [Fe/H]. The mass-weighted scaleheight hZ distribution is a smoothly declining exponential function. High [α/Fe] populations are thicker than low [α/Fe], and the average hZ increases steadily with age, between 200 and 600 pc.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “We expect to get those form the K2 (Howell et al. 2014), TESS (Ricker et al. 2015) and PLATO (Rauer et al. 2014) asteroseismic missions in the near future, as well as isochrone age determination from spectroscopic surveys, such as GALAH (De Silva et al. 2015), Gaia-ESO (Gilmore et al. 2012), APOGEE,”
The Close Binary Fraction of Solar-type Stars Is Strongly Anticorrelated with Metallicity (2018, background): “Such old, low-mass giants tend to be metal-poor (Ratnatunga & Yoss 1991; Carollo et al. 2010; Mackereth et al. 2017).”
StarHorse : a Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars (2017, unknown): “If stellar ages are available as well, they can be used to probe the chemo-dynamical evolution of different Galactic components much more directly (e.g., Zoccali et al. 2003; Haywood et al. 2013; Mitschang et al. 2014; Anders et al. 2017; Mackereth et al. 2017).”
The vertical metallicity gradients of mono-age stellar populations in the Milky Way with the RAVE and Gaia data (2017, background): “What is more, Mackereth et al. (2017) showed that mono-age stellar populations flare even for the highest [α/Fe] (see also Martig et al. 2014).”
Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s) (2017, background): “A decrease of the overall age–Rguide relation can be explained by a combination of the age– velocity dispersion relation and the age–scale length relation (see e.g. Mackereth et al. 2017, and references therein).”