The GALAH survey: neutron-capture elemental abundances for 350 000 Gaia-RVS spectra and the chemodynamics of accreted structures

Das, Pradosh Barun (author), Kos, Janez (author)

We present a comprehensive data-driven spectroscopic analysis of 357 415 red giant stars using Gaia DR3 Radial Velocity Spectrometer (RVS) spectra (8460-8700 Å; $R \approx 11500$), aimed at deriving homogenous stellar parameters and elemental abundances (collectively referred to as stellar labels). We employ The Cannon, a generative model based on 2747 giants in common with GALactic Archaeology with HERMES (GALAH) DR4, adopting GALAH labels (⁠$R \approx 28000$) for training. The resulting model predicts 11 stellar labels for RVS giants: effective temperature (⁠$T_{eff}$), surface gravity ($\mathrm{log} g$⁠), projected rotational velocity ($v \sin{i}$⁠), and abundances of [Fe/H], [Ca/Fe], [Si/Fe], [Ni/Fe], [Ti/Fe], as well as the neutron-capture elements [Zr/Fe], [Ce/Fe], and [Nd/Fe]. Building on these results, we develop a probabilistic framework to chemically identify debris from the Gaia-Sausage-Enceladus (GSE) accretion event. A logistic regression classifier, optimized via Markov chain Monte Carlo sampling and trained on a small reference sample of GSE members and comparison stars, identifies stars with high GSE membership probabilities based solely on their chemical abundances, with the resulting candidates exhibiting distinctive abundance-ratio patterns, including [Ca/Ti], [Ti/Ce], and [Nd/Zr]. Applying independent kinematic constraints yields a robust sample of GSE candidates, demonstrating that the characteristic chemical signatures remain consistent after applying these constraints. This work demonstrates the potential of data-driven analysis techniques to extract detailed chemical information from medium-resolution spectra and establishes a framework for tracing Galactic accretion events using chemical abundances.

• Language: English
• Keywords: stars, galaxies, chemical abundances, galaxy evolution, spectroscopic analysis, GALAH sky survey
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 24 str.
• Numbering: Vol. 550, iss. 4
• PID: 20.500.12556/RUL-191284
• UDC: 524
• ISSN on article: 1365-2966
• DOI: 10.1093/mnras/stag1142
• COBISS.SI-ID: 305278467
• Publication date in RUL: 13.11.2026

Record is a part of a journal

• Title: Monthly notices of the Royal Astronomical Society
• Shortened title: Mon. not. R. Astron. Soc.
• Publisher: Blackwell Science
• ISSN: 1365-2966
• COBISS.SI-ID: 1870180

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: zvezde, galaksije, kemična sestava, razvoj galaksij, spektroskopski pregledi neba, GALAH