Galaxies and Cosmology Seminar

Dec

2025

12:00 pm – 1:00 pm

In Person (view details)

Galaxies and Cosmology Seminar

Description

Tae Bong Jeong, The University of Texas at Austin

Simulating High-redshift Galaxies: Enhancing UV Luminosity with Star Formation Efficiency and a Top-heavy IMF

Recent findings from photometric and spectroscopic JWST surveys have identified large numbers of high-redshift galaxies at z ≳ 10, which appear to form much earlier and exhibit greater UV luminosity than predicted by theoretical work. We aimed to reproduce the brightness of these sources by simulating high-redshift galaxies with cosmological simulations, modifying baryonic subgrid physics. Specifically, we enhanced star formation activity in high-redshift galaxies by either increasing the star formation efficiency up to 100% or adopting a top-heavy initial mass function (IMF). Our simulation results indicate that both increasing star formation efficiency and adopting a top-heavy IMF play crucial roles in boosting the UV luminosity of high-redshift galaxies, potentially exceeding the limiting magnitude of JWST surveys in earlier epochs.

Christian Kragh Jespersen, Princeton University

Connecting the Optical and Infrared

Galaxies are often modelled as composites of separable components with distinct spectral signatures, implying that different wavelength ranges are only weakly correlated. They are not. I will present a data-driven model to predict infrared emission from optical spectra, achieving accuracies of χ² ~ 1 for all photometric bands in WISE, as well as good colors. The model exploits subtle correlations between physical processes and is therefore able to predict typically IR-derived properties like the bolometric luminosity of AGN and dust parameters such as qPAH. Current SED-fitting methods are incapable of making comparable predictions, with misspecification in these models furthermore leading to overconfident and biased extrapolations, as well as correlated biases in star-formation rates and AGN luminosities. To help improve SED models, I will show what features of the optical spectrum are responsible for our improved predictions, and identify several lines (CaII, SrII, FeI, [OII] and Hα), which point to the complex chronology of star formation and chemical enrichment being incorrectly modelled.