Galactoseismology and impacts of the spiral arms

Daisuke Kawata (UCL/MSSL)

We measure stellar age for APOGEE giants using our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy, Ciuca et al. 2024). After de-noising the data, we found a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a rapid chemical enrichment with increasing [Fe/H] and decreasing [Mg/Fe]. Comparing with the Milky Way-like zoom-in cosmological simulation Auriga, we discuss that this could be due to the early epoch of gas-rich merger. We further argue that this could be associated with the last massive merger of our Galaxy, the Gaia-Sausage-Enceladus merger, and discuss how it impacted the formation of the Galactic thick and thin disks and also the Galactic bar. We will also introduce the Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE, Kawata et al. 2024, PASJ, 76, 386). JASMINE has two main science goals: to reveal the Milky Way's central core structure and its formation history from the Gaia-level (~25 uas) astrometry in the NIR Hw-band, (1.0-1.6 um), Galactic centre archaeology survey, which will enable us to more clearly identify the formation epoch of the Galactic bar, and to discover Earth-like habitable exoplanets from the NIR time-series photometry of M-dwarf transits, the exoplanet survey.