StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical structures in the solar vicinity the genuine thick disk and young-alpha rich stars

by A.Queiroz, et al. (2022)


The Gaia mission has added an invaluable wealth of astrometric data for more than a billion stars in our Galaxy. The synergy between Gaia astrometry, photometry, and spectroscopic surveys gives us comprehensive information about the Milky Way. Using the Bayesian isochrone-fitting code StarHorse, we derive distances and extinctions for more than 10 million unique stars observed by both Gaia Data Release 3 as well as public spectroscopic surveys: 557 559 in GALAH+ DR3, 4 531 028 in LAMOST DR7 LRS,347 535 in LAMOST DR7 MRS, 562 424 in APOGEE DR17, 471 490 in RAVE DR6, 249 991 in SDSS DR12 (optical spectra from BOSS and SEGUE), 67 562 in the Gaia-ESO DR3 survey, and 4 211 087 in the Gaia RVS part of Gaia DR3 release. StarHorse can extend the precision of distances and extinctions measurements where Gaia parallaxes alone would be uncertain. For the first time, we also derive stellar age for main-sequence turnoff and subgiant branch stars (MSTO-SGB) (around 4 million stars with age uncertainties typically around 30%, 15% for only SGB stars, depending on the resolution of the survey). With the derived ages in hand, we investigate the chemical-age relations. In particular, the a and neutron-capture element ratios versus age in the solar neighbourhood show trends similar to previous works, hence validating our ages. We use the chemical abundances from local subgiant samples of GALAH DR3, APOGEE DR17 and LAMOST MRS DR7 to map groups with similar chemical compositions and StarHorse ages with the dimensionality reduction technique t-SNE and the clustering algorithm HDBSCAN. We identified three distinct structural kinematical components, without the assumption of any priors. Their kinematic properties confirm them to be the genuine chemical thick disk, the thin disk and a large number of young alpha-rich stars (427), which are also a part of the delivered catalogues. We confirm that the genuine thick disk’s kinematics and age properties are radically different from those of the thin disk, and compatible with high-redshift (z∼2) star-forming disks with high dispersion velocities. We also found a few substructures in the GALAH DR3, thanks to the availability of n-capture elements, which can be associated with the passage of Sagittarius 6.5 Gyr ago.

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