Beyond the two-infall model :  I. Indications for a recent gas infall with Gaia DR3 chemical abundances

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Abstract

Context. The recent Gaia Data Release 3 (DR3) represents an unparalleled revolution in Galactic archaeology, providing numerous radial velocities and chemical abundances for millions of stars as well as all-sky coverage.

Aims We present a new chemical evolution model for the Galactic disc components (high- and low- α sequence stars) designed to reproduce the new abundance ratios provided by the General Stellar Parametriser-spectroscopy module for the Gaia DR3 and constrained by the detailed star formation (SF) histories for both the thick and thin disc stars inferred from previous Gaia releases.

Methods. Sophisticated modelling based on previous Gaia releases have found evidence for narrow episodes of enhanced SF inferred in recent time. Additionally, Gaia DR3 indicated the presence of young (massive) low- α disc stars that show evidence of a recent chemical impoverishment in several elements. In order to reproduce these observables, we propose a new chemical evolution model in which the low- α sequence is generated by two distinct infall episodes. Hence, in this study we compare Gaia DR3 chemical abundances with the predictions of a three-infall chemical evolution model for the high- and low- α components.

Results The proposed three-infall chemical evolution model nicely reproduces the main features of the abundance ratio [X/Fe] versus [M/H] (X=Mg, Si, Ca, Ti, α) of Gaia DR3 stars in different age bins for the considered α elements. Moreover, the most recent gas infall – which started ∼2.7 Gyr ago – allowed us to predict accurately predict the Gaia DR3 young population which has experienced a recent chemical impoverishment.

Conclusions. We extended previous chemical evolution models designed to reproduce APOGEE and APOKASC data in order to predict new Gaia DR3 chemical abundances. To this aim, we proposed a three-infall chemical evolution model to better trace both (i) the young population in Gaia DR3 with evidence of chemical impoverishment and (ii) the SF history from previous Gaia releases.

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Gaia Early Data Release 3 : Summary of the contents and survey properties

A. G. A. Brown, A. Vallenari, T. Prusti … (2021)

Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Aims. A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results. Methods. The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity. Results. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the ( G BP − G RP ) colour are also available. The passbands for G , G BP , and G RP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia -CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Conclusions. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30–40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G , G BP , and G RP is valid over the entire magnitude and colour range, with no systematics above the 1% level