J/A+A/683/A74 Evidence of high redshift Galactic alpha-poor disc (Gent+, 2024)
The Prince and the Pauper:
Evidence for the early high-redshift formation of the Galactic alpha-poor
disc population.
Gent M.R., Eitner P., Serenelli A., Friske J.K.S., Koposov S.E.,
Laporte C.F.P., Buck T., Bergemann M.
<Astron. Astrophys. 683, A74 (2024)>
=2024A&A...683A..74G 2024A&A...683A..74G (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way; Stars, F-type ; Stars, G-type ; Stars, K-type ;
Abundances ; Effective temperatures ; Stars, ages
Keywords: Galaxy: abundances - Galaxy: disk fundamental parameters -
Galaxy: structure
Abstract:
The presence of [alpha/Fe]-[Fe/H] bi-modality in the Milky Way disc has
animated the Galactic archaeology community since more than two
decades.
Our goal is to investigate the chemical, temporal, and kinematical
structure of the Galactic discs using abundances, kinematics, and ages
derived self-consistently with the new Bayesian framework SAPP.
We employ the public Gaia-ESO spectra, as well as Gaia EDR3 astrometry
and photometry. Stellar parameters and chemical abundances are
determined for 13426 stars using NLTE models of synthetic spectra.
Ages are derived for a sub-sample of 2898 stars, including subgiants
and main-sequence stars. The sample probes a large range of
Galactocentric radii, ∼3 to 12kpc, and extends out of the disc
plane to ±2kpc.
Our new data confirm the known bi-modality in the [Fe/H] - [alpha/Fe]
space, which is often viewed as the manifestation of the chemical thin
and thick discs. The over-densities significantly overlap in
metallicity, age, and kinematics, and none of these is a sufficient
criterion for distinguishing between the two disc populations.
Different from previous studies, we find that the alpha-poor disc
population has a very extended [Fe/H] distribution and contains ∼
20% old stars with ages of up to ∼11Gyr.
Our results suggest that the Galactic thin disc was in place early, at
look-back times corresponding to redshifts z∼2 or more. At ages
∼9 to 11Gyr, the two disc structures shared a period of
co-evolution. Our data can be understood within the clumpy disc
formation scenario that does not require a pre-existing thick disc to
initiate a formation of the thin disc. We anticipate that a similar
evolution can be realised in cosmological simulations of galaxy
formation.
Description:
Based on observations made with the ESO/VLT, at Paranal Observatory,
under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey,
PIs G. Gilmore and S. Randich). Also based on observations under
programs 171.0237 and 073.0234., as well as Gaia photometry and
astrometry we derived stellar atmospheric parameters Teff, Logg,
chemical NLTE abundances as well as microturbulence for 13426 stars,
using an automatic pipeline SAPP (2022A&A...658A.147G 2022A&A...658A.147G).
We provide the star identifier from Gaia-ESO DR4 (CName), Teff, Logg,
[Fe/H], [Mg/Fe] in NLTE, Vmic and associated errors.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 86 13426 Catalogue of parameters
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Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- CName Target ID [Gaia-ESO cname]
18- 23 F6.1 K Teff Effective temperature
25- 29 F5.1 K e_Teff Uncertainty on Teff
31- 34 F4.2 [cm/s2] logg Surface gravity
36- 39 F4.2 [cm/s2] e_logg Uncertainty on logg
41- 46 F6.3 [-] [Fe/H] Ratio [Fe/H] in NLTE
48- 52 F5.3 [-] e_[Fe/H] Uncertainty on NLTE [Fe/H] ratio
54- 59 F6.3 [-] [Mg/Fe] Ratio [Mg/Fe] in NLTE
61- 65 F5.3 [-] e_[Mg/Fe] Uncertainty on NLTE [Mg/Fe]
67- 70 F4.2 km/s Vmic Microturbulence in NLTE
72- 75 F4.2 km/s e_Vmic Uncertainty on NLTE Vmic
77- 81 F5.2 Gyr Age Stellar age
83- 86 F4.2 Gyr e_Age Uncertainty on Age
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Acknowledgements:
Matthew Gent, gent(at)mpia.de
(End) Matthew Gent [MPIA, Germany], Patricia Vannier [CDS] 12-Jan-2024