The GALAH survey : data release 4

Buder, Sven (author), Kos, Janez (author), Zwitter, Tomaž (author), Beeson, Kevin Luke (author), Vogrinčič, Rok (author)

The stars of the Milky Way carry the chemical history of our Galaxy in their atmospheres as they journey through its vast expanse. Like barcodes, we can extract the chemical fingerprints of stars from high-resolution spectroscopy. The fourth data release (DR4) of the Galactic Archaeology with HERMES (GALAH) Survey, based on a decade of observations, provides the chemical abundances of up to 32 elements for 917 588 stars that also have exquisite astrometric data from the Gaia satellite. For the first time, these elements include life-essential nitrogen to complement carbon, and oxygen as well as more measurements of rare-earth elements critical to modern-life electronics, offering unparalleled insights into the chemical composition of the Milky Way. For this release, we use neural networks to simultaneously fit stellar parameters and abundances across the whole wavelength range, leveraging synthetic grids computed with Spectroscopy Made Easy. These grids account for atomic line formation in non-local thermodynamic equilibrium for 14 elements. In a two-iteration process, we first fit stellar labels to all 1 085 520 spectra, then co-add repeated observations and refine these labels using astrometric data from Gaia and 2MASS photometry, improving the accuracy and precision of stellar parameters and abundances. Our validation thoroughly assesses the reliability of spectroscopic measurements and highlights key caveats. GALAH DR4 represents yet another milestone in Galactic archaeology, combining detailed chemical compositions from multiple nucleosynthetic channels with kinematic information and age estimates. The resulting dataset, covering nearly a million stars, opens new avenues for understanding not only the chemical and dynamical history of the Milky Way but also the broader questions of the origin of elements and the evolution of planets, stars, and galaxies.

• Language: English
• Keywords: surveys, Galaxy, fundamental parameters
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Publication date: 01.05.2025
• Year: 2025
• Number of pages: 42 str.
• Numbering: Vol. 42, art. id. ǂe051
• PID: 20.500.12556/RUL-169937
• UDC: 524.6
• ISSN on article: 1448-6083
• DOI: 10.1017/pasa.2025.26
• COBISS.SI-ID: 240010499
• Publication date in RUL: 19.06.2025

Record is a part of a journal

• Title: Publications of the Astronomical Society of Australia
• Publisher: CSIRO Publishing
• ISSN: 1448-6083
• COBISS.SI-ID: 521631513

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: pregledi, Galaksija, osnovni parametri

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P1-0188-2022
• Name: Astrofizika in fizika atmosfere