The GALAH survey: Data release 4
Journal article, 2025
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.
stars: abundances
methods: observational
stars: fundamental parameters
Surveys
the Galaxy
methods: data analysis
Author
Sven Buder
ARC Centre of Excellence for All-sky Astrophysics
Australian National University
Janez Kos
University of Ljubljana
Xi Ella Wang
ARC Centre of Excellence for All-sky Astrophysics
Australian National University
Madeleine Mckenzie
Australian National University
ARC Centre of Excellence for All-sky Astrophysics
Madeleine Howell
ARC Centre of Excellence for All-sky Astrophysics
Monash University
Sarah Martell
ARC Centre of Excellence for All-sky Astrophysics
University of New South Wales (UNSW)
Michael R. Hayden
ARC Centre of Excellence for All-sky Astrophysics
University of New South Wales (UNSW)
University of Oklahoma
The University of Sydney
Daniel B. Zucker
ARC Centre of Excellence for All-sky Astrophysics
Macquarie University
Thomas Nordlander
ARC Centre of Excellence for All-sky Astrophysics
Uppsala University
Australian National University
Benjamin Montet
University of New South Wales (UNSW)
Gregor Traven
University of Ljubljana
Joss Bland-Hawthorn
ARC Centre of Excellence for All-sky Astrophysics
The University of Sydney
Gayandhi M. De Silva
Macquarie University
ARC Centre of Excellence for All-sky Astrophysics
Kenneth Freeman
ARC Centre of Excellence for All-sky Astrophysics
Australian National University
Geraint Lewis
The University of Sydney
Karin Lind
AlbaNova University Center
Sanjib Sharma
Space Telescope Science Institute (STScI)
Jeffrey D. Simpson
University of New South Wales (UNSW)
ARC Centre of Excellence for All-sky Astrophysics
Dennis Stello
The University of Sydney
ARC Centre of Excellence for All-sky Astrophysics
Aarhus University
University of New South Wales (UNSW)
Tomaz Zwitter
University of Ljubljana
Anish Amarsi
Uppsala University
Joseph Armstrong
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Kirsten Banks
ARC Centre of Excellence for All-sky Astrophysics
University of New South Wales (UNSW)
Mark Beavis
University of Southern Queensland
Kevin Luke Beeson
University of Ljubljana
Boquan Chen
ARC Centre of Excellence for All-sky Astrophysics
Australian National University
Ioana Ciucǎ
ARC Centre of Excellence for All-sky Astrophysics
Australian National University
Gary S. Da Costa
Australian National University
ARC Centre of Excellence for All-sky Astrophysics
Richard De Grijs
International Space Science Institute-Beijing
Macquarie University
Bailey Martin
Australian National University
David Moise Nataf
University of Iowa
Melissa Ness
Australian National University
ARC Centre of Excellence for All-sky Astrophysics
Adam D. Rains
Uppsala University
Tim Scarr
Australian National University
Rok Vogrinčič
University of Ljubljana
Zixian Purmortal Wang
The University of Sydney
ARC Centre of Excellence for All-sky Astrophysics
University of Utah
R. A. Wittenmyer
University of Southern Queensland
Yi Anne Xie
ARC Centre of Excellence for All-sky Astrophysics
Australian National University
Publications Astronomical Society of Australia
1323-3580 (ISSN) 1448-6083 (eISSN)
Vol. 42 e051Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1017/pasa.2025.26