The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14

Rojas-Arriagada, Á.; Zoccali, M.; Schultheis, M.; Recio–Blanco, A.; Zasowski, Gail; Minniti, D.; Jönsson, Henrik; Cohen, Roger E.

doi:10.1051/0004-6361/201834126

Cited by 50 publications

(32 citation statements)

References 61 publications

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“…Bensby et al (2013Bensby et al ( , 2017 studied the abundance distribution of bulge stars using microlensed dwarfs and subgiants within 1 kpc of the Galactic center. They found that ([Fe/H], [α/Fe]) distribution of stars in the Galactic bulge are very similar to the sequence found in the inner disc (see also Rojas-Arriagada et al 2019) . This is correctly predicted by our model.…”

Section: Relation To Other Studiesmentioning

confidence: 55%

Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$α/\rm Fe]$ Double Sequence

Sharma,

Hayden,

Bland-Hawthorn

2020

Preprint

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The ([α/Fe], [Fe/H]) distribution of Milky Way stars shows at least two distinct sequences, which have traditionally been associated with the thin and thick disc components. The abundance distribution varies systematically with location R and |z| across the Galaxy. Using an analytical chemodynamical model that includes the effects of radial migration and kinematic heating, we show that it is possible to reproduce the observed abundance distribution at different locations. Unlike some earlier models, our scheme does not require a distinct thick disc component emerging from a separate evolutionary path. The proposed model has a continuous star formation history and a continuous age velocity dispersion relation. Moreover, [α/Fe] is constant for stellar ages less than 8 Gyr, but increases sharply for older stars over a time scale of 1.5 Gyr. The gap between the two sequences is due to this sharp transition. We show that the high-[α/Fe] sequence at the low metallicity end is simply a pile-up of old stars. At the high metallicity end, we find a sequence of stars having different ages with a similar birth radius that originated in the inner disc. Our model successfully explains the uniformity of the locus of the high-[α/Fe] sequence across different locations. The low-[α/Fe] sequence contains stars with different birth radii that owes its existence to radial migration. For the low-[α/Fe] sequence, angular momentum is anti-correlated with [Fe/H], and the model can reproduce this trend at different Galactic locations. If radial migration is not included, the model fails to generate the double sequence and instead shows only a single sequence. Our simple scheme has major advantages over earlier chemodynamical models, as we show.

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Section: Relation To Other Studiesmentioning

confidence: 55%

Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$α/\rm Fe]$ Double Sequence

Sharma,

Hayden,

Bland-Hawthorn

2020

Preprint

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“…In contrast to Rojas-Arriagada et al (2019), however, the two blobs define completely detached sequences, without merging, thus showing a true chemical discontinuity. The new maps show that the chemical discontinuity seen in the solar neighborhood bin (mostly studied also by other surveys -middle row, 4th column), extends towards the Bulge, and become completely separated, being very similar to what was found by Fuhrmann (1998Fuhrmann ( , 2011 within 25 pc but now extended to larger metallicities (as expected given the observed abundance gradients in the galactic disc).…”

Section: For Discussion)mentioning

confidence: 91%

From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys

Queiroz,

Anders,

Chiappini

et al. 2019

Preprint

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We combine high-resolution spectroscopic data from APOGEE-2 survey Data Release 16 (DR16) with broad band photometric data from several sources, as well as parallaxes from Gaia Data Release 2 (DR2). Using the Bayesian isochrone-fitting code StarHorse, we derive distances, extinctions and astrophysical parameters for around 388,000 APOGEE stars, achieving typical distance uncertainties of ∼ 11% for APOGEE giants, ∼ 5% for APOGEE dwarfs, as well as as well as extinction uncertainties of ∼ 0.07mag, when all the photometric information is available. StarHorse uncertainties vary with the input spectroscopic catalogue, with the available photometry, and with the parallax uncertainties. The value-added catalog generated here was compared to the asteroseismic CoROGEE catalogue (for which distances and extinctions are also updated according to the new DR16 spectroscopic inputs) showing good agreement, but suggesting smaller parallax shifts in the mid plane fields with respect to those found in the Kepler field. To illustrate the impact of the new StarHorse results we show an analysis of the chemical spatial dependency of Galactic plane stars. Thanks to Gaia DR2 and the now larger coverage of APOGEE-2 (including APOGEE-south) we obtain an extended map of the Galactic plane, now reaching the inner-most parts of the Galaxy and providing an unprecedented coverage of the disk close to the Galactic mid-plane. The distance and extinction improvements unveil the presence of the bar in a density diagram, as well as the striking chemical duality in the innermost regions of the disk, now clearly extending to the bulge. For the first time we are able to have a much less fragmented view of our Galaxy. We complement this paper with distances and extinctions for stars in other public released spectroscopic surveys:

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“…We adopt the stellar parameters and abundances from the APOGEE DR16 catalogue, and spectro-photometric distances with the procedure described in Rojas-Arriagada et al (2017). Since the magnesium abundance has been shown to be the most reliably measured α-element in the APOGEE survey (Rojas-Arriagada et al 2019;Jönsson et al in (Pinsonneault et al 2018). Note that the ages of stars become less reliable at [Fe/H]< −0.5, owing to the lack of training set stars and the effects of extra-mixing at these metallicities (Mackereth et al 2019).…”

Section: Datamentioning

confidence: 99%

The age–chemical abundance structure of the Galactic disc – II. α-dichotomy and thick disc formation

Lian

Thomas

Maraston

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We extend our previous work on the age-chemical abundance structure of the Galactic outer disc to the inner disc (4<r <8 kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]–[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multi-phase inner disc formation scenario that matches the observed bimodal [Mg/Fe]–[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes 6 Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times (t ∼ 1 Gyr) and the second one 6 Gyr later at a cosmic time of t ∼ 7 Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-α sequence, and the second starburst leads to the formation of the metal-poor low-α sequence. The metal-rich low-α stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the α-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z >1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively.

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The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14

Cited by 50 publications

References 61 publications

Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$α/\rm Fe]$ Double Sequence

Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$α/\rm Fe]$ Double Sequence

From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys

The age–chemical abundance structure of the Galactic disc – II. α-dichotomy and thick disc formation

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