Article

The GALAH Survey: Neutron-Capture Elemental Abundances for 350 000 <i>Gaia</i> -RVS spectra and the Chemodynamics of Accreted Structures

P. K. DasEuropean Southern Observatory , Karl-Schwarzschild-Str 2, D-85748, Garching via Munich ,Daniel B ZuckerAstrophysics and Space Technologies Research Centre, Macquarie University , Sydney, NSW 2109 ,Aldo Mura-GuzmánAstrophysics and Space Technologies Research Centre, Macquarie University , Sydney, NSW 2109 ,Nicholas W. BorsatoAstrophysics and Space Technologies Research Centre, Macquarie University , Sydney, NSW 2109 ,Gayandhi M De SilvaResearch School of Astronomy and Astrophysics, The Australian National University , Canberra, ACT 2611 ,Sven BuderACCESS-NRI, Australian National University , Canberra, ACT 2601 ,Diane FeuilletObservational Astrophysics, Department of Physics and Astronomy, Uppsala University , Box 516, SE-751 20, Uppsala ,Thomas NordlanderTheoretical Astrophysics, Department of Physics and Astronomy, Uppsala University , Box 516, SE-751 20, Uppsala ,Melissa NessResearch School of Astronomy and Astrophysics, The Australian National University , Canberra, ACT 2611 ,Sarah L. MartellSchool of Physics, University of New South Wales , Sydney, NSW 2052 ,Janez KosFaculty of Mathematics and Physics, University of Ljubljana , Jadranska 19, 1000, Ljubljana ,J Bland-HawthornSydney Institute for Astronomy, School of Physics, A28, The University of Sydney , Sydney, NSW 2006 ,Ken C. FreemanResearch School of Astronomy and Astrophysics, The Australian National University , Canberra, ACT 2611 ,Andrew R. CaseyMonash UniversityGeraint F. LewisSydney Institute for Astronomy, School of Physics, A28, The University of Sydney , Sydney, NSW 2006 ,Dennis StelloSchool of Physics, University of New South Wales , Sydney, NSW 2052 ,Richard de GrijsInternational Space Science Institute–Beijing , 1 Nanertiao, Zhongguancun, Hai Dian District, Beijing 100190 ,

2026en

ABI

Abstract

ABSTRACT 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; $R \approx 11\,500$), 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 ($R \approx 28\,000$) for training. The resulting model predicts 11 stellar labels for RVS giants: effective temperature ($T_{\mathrm{eff}}$), surface gravity ($\log g$), 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.

Identifiers

DOI: 10.1093/mnras/stag1142

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