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The formation and evolution of galaxies is one of the great outstanding problems of modern astrophysics. The goal of galactic archaeology is to reconstruct the lost stellar substructures of the early Milky Way, thereby obtaining a detailed physical picture of its formation and evolution.

The stellar abundance pattern over many elements reflects the chemical state of the gas from which stars form and is like a stellar DNA profile. By exploring stellar chemistry, we can identify stars that are part of the debris of common yet now-dispersed stellar building blocks, and also those stars which came in from externally accreted satellite galaxies, a technique known as chemical tagging.

The GALactic Archaeology with HERMES (GALAH) survey is a Large Observing Program using the HERMES instrument with the Anglo-Australian Telescope of the Australian Astronomical Observatory. HERMES provides simultaneous spectra for 400 objects in four wavelength bands tailored to obtain a range of chemical element lines, from light elements up to heavy neutron-capture elements. Using this instrument, GALAH will obtain precise radial velocities and abundances of over 15 different chemical elements per star for over a million stars. Elemental abundances representing the main nucleosynthetic processes in both dwarf and giant stars will allow chemical tagging of the individual stars to their original formation event, and accurate velocities will permit differentiation of stars by their dynamics. The resulting data sets will yield a comprehensive view of the formation and evolution of the Galaxy, enabling the reconstruction of the original stellar building blocks. It will allow us to investigate the history of star formation in the Galaxy, the regularity, and importance, of merger events, and the changes in stellar dynamics over time.

For general background information on the astronomical techniques used by this survey, please read our For the Public page. For those who would like more detail, please see the HERMES GALAH Survey: Overview document. This site also provides useful information about the GALAH design and strategy, scientific goals, and data analysis. The GALAH Survey Team will be releasing stellar information from GALAH on a regular schedule.