A Radial Age Gradient in the Geometrically Thick Disk of the Milky Way

Martig, Marie; Minchev, Ivan; Ness, Melissa; Fouesneau, M.; Rix, Hans─Walter

doi:10.3847/0004-637x/831/2/139

Cited by 93 publications

(98 citation statements)

References 56 publications

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“…They show from numerical simulations that a radial gradient in age naturally emerges due to the flaring of the populations, if younger populations are more extended than older ones. Martig et al (2016) by using APOGEE data reinforces the results found by Minchev et al (2015). In our study, the younger disc populations are indeed more extended than older ones, and they also flare earlier.…”

Section: How Does the Galaxy Flare In The Outskirtssupporting

confidence: 81%

Evolution over time of the Milky Way’s disc shape

Amôres

Robin

Reylé

2017

A&A

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Context. Galactic structure studies can be used as a path to constrain the scenario of formation and evolution of our Galaxy. The dependence with the age of stellar population parameters would be linked with the history of star formation and dynamical evolution. Aims. We aim to investigate the structures of the outer Galaxy, such as the scale length, disc truncation, warp and flare of the thin disc and study their dependence with age by using 2MASS data and a population synthesis model (the so-called Besançon Galaxy Model). Methods. We have used a genetic algorithm to adjust the parameters on the observed colour-magnitude diagrams at longitudes 80 • ≤ ≤ 280 • for |b| ≤ 5.5 • . We explored parameter degeneracies and uncertainties. Results. We identify a clear dependence of the thin disc scale length, warp and flare shapes with age. The scale length is found to vary between 3.8 kpc for the youngest to about 2 kpc for the oldest. The warp shows a complex structure, clearly asymmetrical with a node angle changing with age from approximately 165 • for old stars to 195 • for young stars. The outer disc is also flaring with a scale height that varies by a factor of two between the solar neighbourhood and a Galactocentric distance of 12 kpc. Conclusions. We conclude that the thin disc scale length is in good agreement with the inside-out formation scenario and that the outer disc is not in dynamical equilibrium. The warp deformation with time may provide some clues to its origin.

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Section: How Does the Galaxy Flare In The Outskirtssupporting

confidence: 81%

Evolution over time of the Milky Way’s disc shape

Amôres

Robin

Reylé

2017

A&A

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“…Martig et al (2015) have found a tight correlation between the masses determined from the standard seismic scaling relations and the [C/N] measurement from APOGEE. They determine a model for stellar mass and age as a function of C and N abundance measurements.…”

Section: Introductionmentioning

confidence: 99%

“…Following this approach, Martig et al (2015) have used red giants in the APOKASC sample of stars, for which seismic parameters are known from Kepler (Pinsonneault et al 2014 (Ahn et al 2014). Martig et al (2015) have found a tight correlation between the masses determined from the standard seismic scaling relations and the [C/N] measurement from APOGEE.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Determination of Masses (And Implied Ages) for Red Giants

Ness

Hogg

Rix

et al. 2016

ApJ

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229

296

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The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the Kepler and APOGEE surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using TheCannon, which can determine stellar masses to ∼0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to ∼0.2 dex (40%). We show that TheCannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 70,000 giants (including 20,000 red clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center toR 20 kpc). We show that the age information in the spectra is not simply a corollary of the birth-material abundances

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“…However, the shear number of stars in the solar circle cut (51948) versus the thick-disk cut (8600) gives a misleading impression, as the wings of the low-α distribution are much easier to see when you display over six times more stars. In addition, if we compare thin-disk stars of similar age and α abundance to NGC 6791, we find that their median distance (R GC ) is 2-3 kpc closer to the Galactic center than the present location of NGC 6791 (see Figure 1 of Martig et al 2016).…”

Section: Unlikely Origins For Ngc 6791mentioning

confidence: 99%

Timing the Evolution of the Galactic Disk with NGC 6791: An Open Cluster with Peculiar High-α Chemistry as Seen by APOGEE

Linden

Pryal

Hayes

et al. 2017

ApJ

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We utilize elemental-abundance information for Galactic red giant stars in five open clusters (NGC 7789, NGC 6819, M67, NGC 188, and NGC 6791) from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) DR13 dataset to age-date the chemical evolution of the high-and low-α element sequences of the Milky Way. Key to this time-stamping is the cluster NGC 6791, whose stellar members have mean abundances that place it in the high-α, high-[Fe/H] region of the [α/Fe]-[Fe/H] plane. Based on the cluster's age (∼ 8 Gyr), Galactocentric radius, and height above the Galactic plane, as well as comparable chemistry reported for APOGEE stars in Baade's Window, we suggest that the two most likely origins for NGC 6791 are as an original part of the thick-disk, or as a former member of the Galactic bulge. Moreover, because NGC 6791 lies at the high metallicity end ([Fe/H] ∼ 0.4) of the high-α sequence, the age of NGC 6791 places a limit on the youngest age of stars in the high-metallicity, high-α sequence for the cluster's parent population (i.e., either the bulge or the disk). In a similar way, we can also use the age and chemistry of NGC 188 to set a limit of ∼ 7 Gyr on the oldest age of the low-α sequence of the Milky Way. Therefore, NGC 6791 and NGC 188 are potentially a pair of star clusters that bracket both the timing and the duration of an important transition point in the chemical history of the Milky Way.

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A Radial Age Gradient in the Geometrically Thick Disk of the Milky Way

Cited by 93 publications

References 56 publications

Evolution over time of the Milky Way’s disc shape

Evolution over time of the Milky Way’s disc shape

Spectroscopic Determination of Masses (And Implied Ages) for Red Giants

Timing the Evolution of the Galactic Disk with NGC 6791: An Open Cluster with Peculiar High-α Chemistry as Seen by APOGEE

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