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| GALAH Survey | |
|---|---|
| Name | GALAH Survey |
| Abbreviation | GALAH |
| Discipline | Astronomy |
| Country | Australia |
| Observatory | Anglo-Australian Telescope |
| Instrument | HERMES spectrograph |
| Start | 2013 |
| Status | Completed / ongoing |
GALAH Survey The GALAH Survey is a large-scale stellar spectroscopic program that mapped the chemical abundances and kinematics of stars in the Milky Way using the Anglo-Australian Telescope and the HERMES spectrograph. It aims to enable chemical tagging and reconstruct the Galactic archaeology of the Galactic disk by measuring detailed element abundances and radial velocities for up to a million stars. The project has interfaced with major projects and institutions such as the European Space Agency, Gaia (spacecraft), Sloan Digital Sky Survey, and the Australian Astronomical Observatory.
The survey was conceived to exploit advances in multi-object spectroscopy exemplified by instruments on the Anglo-Australian Telescope, the Very Large Telescope, and the Subaru Telescope to perform a homogeneous chemical census of the Solar neighbourhood, the Galactic thin disk, and the Galactic thick disk. It leverages complementary astrometry from Gaia (spacecraft) and photometry from projects including Two Micron All Sky Survey, Pan-STARRS, and SkyMapper. Leadership and significant contributions came from teams associated with Australian National University, Monash University, University of Cambridge, University of Sydney, and the Max Planck Institute for Astronomy.
GALAH used the HERMES spectrograph mounted on the 2dF fibre positioner at the Anglo-Australian Telescope to obtain intermediate-resolution spectra across four optical channels. The instrument design borrowed concepts from multi-fibre facilities on the W. M. Keck Observatory and the European Southern Observatory while integrating calibration strategies akin to those used in the Sloan Digital Sky Survey and the RAdial Velocity Experiment. The survey strategy emphasized high signal-to-noise for chemical precision, spectrophotometric stability drawing on methods used by the European Southern Observatory teams, and survey software pipelines developed in collaboration with groups at Cambridge University and Carnegie Institution for Science.
Targets were selected to sample stars across the Hertzsprung–Russell diagram in the southern sky, focusing on dwarfs and giants with magnitudes compatible with HERMES sensitivity limits. The selection utilized catalogs from Gaia (spacecraft), Two Micron All Sky Survey, Hipparcos Catalogue, and photometric surveys such as SkyMapper and APASS. Observing campaigns coordinated scheduling and fibre allocation methods influenced by strategies employed in the Sloan Digital Sky Survey and the LAMOST Experiment to maximize field tiling, completeness, and repeat observations for radial velocity stability.
Data reduction pipelines combined techniques from the Sloan Digital Sky Survey data processing heritage with bespoke algorithms developed by teams at Australian National University and Monash University. The analysis employed spectrum synthesis and line-list calibration comparable to methods used by the RAdial Velocity Experiment and abundance pipelines used by the Apache Point Observatory Galactic Evolution Experiment. Stellar parameters and abundances were validated against benchmark stars from the Gaia-ESO Survey and the Kepler mission asteroseismic samples, while radial velocities were cross-checked with standards from the International Astronomical Union lists. Machine learning and data-driven methods inspired by work at Flatiron Institute and Max Planck Institute for Astrophysics were used to refine classifications.
Results from the survey have probed chemical gradients in the Galactic disk, identified kinematic substructures associated with past accretion events like those linked to the Gaia Sausage and the Helmi stream, and constrained models of stellar migration influenced by perturbations from the Galactic bar and Sagittarius dwarf spheroidal galaxy. GALAH abundance patterns have been compared with simulations from groups at the Institute for Computational Cosmology and chemical evolution models developed at the Max Planck Institute for Astrophysics and Monash University. The survey contributed to studies of stellar ages using techniques allied to the Kepler mission asteroseismology program and to investigations of open clusters including comparisons to results from the GALACTICNUCLEUS survey and the APOGEE program.
The collaboration comprised institutions such as Australian National University, Monash University, University of Sydney, University of Cambridge, Max Planck Institute for Astronomy, and partnerships with data providers including Gaia (spacecraft) and the Sloan Digital Sky Survey. Data releases followed coordinated schedules comparable to those from the Gaia Archive and the Sloan Digital Sky Survey data releases, providing value-added catalogs, derived stellar parameters, and abundance measurements. The project adhered to community standards set by organizations like the International Astronomical Union and engaged with archives such as the European Southern Observatory and national data centers.
The survey's legacy includes an extensive chemical-kinematic catalog that will continue to be mined alongside future datasets from missions and facilities like Gaia (spacecraft), the Vera C. Rubin Observatory, the James Webb Space Telescope, and next-generation spectrographs on the European Southern Observatory telescopes. Its methodology influences the design of subsequent Galactic archaeology programs at institutions such as the Max Planck Institute for Astronomy and universities involved in the original collaboration. Long-term scientific impact is expected in fields touched by the project including studies tied to the Gaia Sausage discovery, chemical tagging efforts inspired by the APOGEE program, and comparisons with cosmological simulations produced by teams at the Institute for Computational Cosmology.
Category:Stellar spectroscopic surveys