On the metal-poor edge of the Milky Way "thin disc"

Emma Fernández-Alvar, Georges Kordopatis, Vanessa Hill, Giuseppina Battaglia, Carme Gallart, Isaure González Rivera de la Vernhe, Guillaume Thomas, Federico Sestito, Anke Ardern-Arentsen, Nicolas Martin, Akshara Viswanathan, Else Starkenburg

Research output: Contribution to journalArticlepeer-review

Abstract

The emergence of the disc in our Galaxy and the relation of the thick and thin disc formation and evolution is still a matter of debate. The chemo-dynamical characterization of disc stars is key to resolve this question, in particular at parameter regimes where both disc components overlap, such as the region around [Fe/H] $\sim$ $-0.7$ corresponding to the thin disc metal-poor end. In this paper we re-assess the recent detection of a metal-poor extension of stars moving with thin-disc-like rotational velocities between -2 < [Fe/H] < -0.7 that was made based on metallicity estimates obtained from photometric data and their rotational velocity distribution. We explore the chemo-dynamical properties of metal-poor stars within the recent Gaia third data release (DR3), which includes the first catalogue of metallicity estimates from the Radial Velocity Spectrometer (RVS) experiment. We complement them with the two largest high-resolution ($\lambda/d\lambda$ > 20,000) spectroscopic surveys available, the GALAH DR3 and the APOGEE DR17. We confirm that there are high angular-momentum stars moving in thin-disc-like orbits, i.e., with high angular momentum $\rm L_{z}/J_{tot}$ > 0.95, and close to the Galactic plane, $\rm |Z_{max}|$ < 750 pc, reaching metallicity values down to [Fe/H] $\sim-1.5$. We also find tentative evidence of stars moving on such orbits at lower metallicities, down to [Fe/H] $\sim -2.5$, although in smaller numbers. Based on their chemical trends the fast rotators with [Fe/H] < -1 would have formed in a medium less chemically evolved than the bulk of the thick disc. Fast rotators with chemical abundances typical of the thin disc appear at metallicities between -1 < [Fe/H] < -0.7.
Original languageEnglish
Article numberA151
Pages (from-to)1-11
Number of pages11
JournalAstronomy & Astrophysics
Volume685
Early online date17 Feb 2024
DOIs
Publication statusPublished - 30 May 2024

Keywords

  • astro-ph.GA

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