Title：The Milky Way: A template for disk galaxy chemical evolution or a unique case?

Speaker：Boquan Erwin Chen( Australian National University)

Time: July 25th, Thursday, 10 am

Tencent Meeting：379-810-924 password: 6360

Location: The small conference room at the 3rd floor

Abstract：

The chemical evolution of the Milky Way offers a unique perspective on the processes shaping our Galaxy. Early studies suggested that two or three infall episodes might be necessary to account for the observed chemical distribution. However, replicating the Milky Way's chemical evolution with a single continuous infall episode using galactic chemical evolution (GCE) models has been a significant challenge.

In this talk, we will present our successful attempt at this challenge. Our model incorporates comprehensive nucleosynthesis yields and several key physical processes in galaxy evolution, including gas feedback from supernovae and star formation, gas infall and radial inflow, and the radial and vertical migration of stars. We focus on replicating the patterns seen in two key abundance ratios: [Fe/H] and [α/Fe]. Iron (Fe) and alpha (α) elements are primarily produced by Type Ia and core-collapse supernovae, respectively. Specifically, we aim to replicate the shapes and relative density of the two [α/Fe] sequences as functions of Galactocentric distance (R) and height from the disk plane (|z|), known as the [α/Fe] bimodality phenomenon.

Our model successfully replicates the ([Fe/H], [α/Fe]) distribution as a function of R and |z| in the Milky Way. We identified three key factors responsible for the observed variation: A high initial star formation rate (SFR) created a large reservoir of white dwarfs, launching the Galaxy to a high initial metallicity.

A significant number of Type Ia supernovae exploded within a short period, causing a rapid decrease in [α/Fe], while the SFR simultaneously dropped, resulting in few stars with intermediate [α/Fe] values. The outward migration of high-[α/Fe] stars born in the inner regions and the upward migration of low-[α/Fe] stars born in the disk plane shaped the current spatial distribution. Our findings demonstrate that a single continuous infall episode can replicate the complex chemical patterns observed in our Galaxy. This suggests that the chemical evolution of the Milky Way could serve as a template for other disk galaxies, rather than being a unique event shaped by its distinct history. Our results imply that [α/Fe] bimodality could be a common feature among disk galaxies.

CV：Boquan Erwin Chen, is currently a postdoc fellow at the Australian National University. He received his Bachelor's and Master's at the University of Wisconsin-Madison and PhD from University of Sydney. He worked on chemical tagging, the Orion star forming complex, and developing clustering algorithms and is currently working on the chemical evolution of the Milky Way observed in large-scale spectroscopic surveys.