| Speaker: | Chiaki Kobayashi (University of Hertfordshire, UK) |
|---|---|
| Title: | Cosmic chemical enrichment in the era of JWST |
| Date (JST): | Tue, Dec 16, 2025, 15:30 - 17:00 |
| Place: | Seminar Room A |
| Abstract: |
The James Webb Space Telescope is expected to find the first galaxies - those hosting metal-free (known as Pop III) stars. Surprisingly, though, galaxies with strong metal lines have been detected indicating unusual chemical composition (e.g. high N/O ratio). During the Big Bang, only light elements such as hydrogen and helium were produced. Carbon and heavier elements are created inside stars and are ejected when they die. Iron-peak and neutron capture elements are further produced by binaries - Type Ia supernovae and neutron star mergers, respectively. Elemental abundances of stars, together with kinematics from the Gaia satellite, have been extremely useful for constraining stellar astrophysics, as well as the star formation and chemical enrichment history of the Galaxy. This approach, Galactic Archaeology, can now be applied to external galaxies thanks to spectroscopic surveys of galaxies across cosmic time, such as with Subaru's Prime Focus Spectrograph (PFS). For comparing to these observations, my team has been running hydrodynamical simulations following detailed chemical evolution from cosmological initial conditions. Metallicity is higher in more massive galaxies (leading to the mass-metallicity relation), and at the centre of galaxies (causing metallicity radial gradients) ― simulations can successfully reproduce these relations at the current epoch, but not so at higher redshifts. The observed high N/O ratios can be explained with Wolf Rayet stars under intermittent star formation, or may indicate the existence of very or super massive stars linking to the origin of super-massive black holes. Using more elements (CNO, Ne, and Ar), it will be possible to constrain these scenarios. |
