Disk Assembly of the Milky Way Suggested from the Time-resolved Chemical Abundance

Abstract

Both simulations and observations suggest that the disk assembly of galaxies is governed by the interplay between coplanar gas inflow, ex-planar gas outflow, and in situ star formation on the disk, known as the leaky accretion disk. This scenario predicts a strong connection between radial distributions of star formation and chemical abundances. The Milky Way, being the sole Galaxy where we can reliably measure star formation histories and the corresponding temporally resolved chemical abundances with individual stars, provides a unique opportunity to scrutinize this scenario. Based on the recent large spectroscopic and photometric surveys of Milky Way stars, we obtain the radial profiles of magnesium abundance ([Mg/H]) and star formation rate surface density at different lookback times. We find the radial profiles of [Mg/H] can be well-reproduced using the leaky accretion disk model with only two free parameters for stars formed within 4 Gyr, as well as the flattening at large radii of metallicity profiles traced by H ii regions and Cepheids. Furthermore, the constraint effective yield of the Milky Way and nearby galaxies shows broad consistency with the theoretical predictions from the stellar chemical evolution model with a mass-loading factor of 0–2. These results support that the recent assembly of the Milky Way adheres to the leaky accretion disk scenario, bridging the disk formation of our home Galaxy to the big picture of disk formation in the Universe.

Keywords

• Galaxy accretion disks
• Milky Way formation
• Metallicity