Spectroscopic surveys of the Galaxy reveal that its disc stars exhibit a spread, or even a bimodality, in alpha abundance ([alpha/Fe]) at fixed iron abundance ([Fe/H]). The origin of these diverse stellar populations is not well understood. I will discuss a new study in which we explore the abundance evolution of Milky Way-like galaxies in the EAGLE simulations, and find that bimodality similar to that seen in the Galaxy is rare, appearing in only 5% of our sample. Bimodal [alpha/Fe] distributions arise in galaxies whose gas accretion histories exhibit episodes of significant infall at both early and late times, with the former fostering more intense star formation than the latter. The shorter characteristic consumption timescale of gas accreted in the earlier episode suppresses its enrichment with iron synthesised by Type Ia supernovae, resulting in the formation of an alpha-rich sequence. We posit that the rarity of bimodal sequences is a consequence of an early gas accretion episode requiring the mass accretion history of a galaxy's dark matter halo to exhibit a phase of unusually rapid growth at early epochs. This rarity may also indicate that the Milky Way's elemental abundance patterns, and its accretion history, are not representative of the broader population of ~L* disc galaxies.
Unless announced otherwise, the lunch talks start at 12:30 sharp. The approximate duration of the lunch talk is given above, and additional time will be given for questions and discussion following the presentation. Please make sure that you take ample time to pick up your lunch beforehand.
Information for Speakers and Hosts: Talks by internal speakers are limited to 20 minutes, with additional time for questions. Visiting speakers can have up to 30 minutes, with additional time for questions. Hosts are responsible for bringing the speaker to the correct room in ample time to set up laptops etc., and for ensuring the speaker also has time for lunch.
For questions and/or suggestions concerning the lunch talks, please contact Themiya Nanayakkara () or Alvaro Hacar ()).