Age, Chemistry, and Kinematics of the Inner Galaxy Revealed by MUSE

Abstract

The bar/bulge and inner disk are fundamental building blocks of the Milky Way, containing a large fraction of its stellar mass. However, stars in these regions are faint, crowded, and have high extinction, which makes studying their formation and evolution challenging. Using the integral-field spectrograph MUSE with adaptive-optics on the Very Large Telescope, we overcome these limitations and measure accurate ages, chemical abundances, and line-of-sight velocities for 98 main-sequence turn-off and subgiant branch stars with $R_{gc}<3.5$ kpc in Baade's Window. We find that 17% stars have ages younger than 5 Gyr, and the age distribution reveals multiple peaks at 3.1, 4.8, 7.6, and 10.8 Gyr, indicating that star formation in the inner Galaxy occurred in multiple episodes. These stars are predominantly metal-rich but span a broad metallicity range ($-1.2<$[Fe/H]$<+0.6$). The [$\alpha$/Fe]-[Fe/H] distribution shows both $\alpha$-rich and $\alpha$-poor sequences, with most stars being metal-rich and low-[$\alpha$/Fe]. Our results demonstrate that IFUs enable reliable measurements of stellar parameters even in the most crowded regions of the Milky Way, opening a new pathway to study the chemodynamical evolution of the inner Galaxy.