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【DoA Seminar】May 21st by Shengdong Lu（Durham University）
Description
Title：Let There Be Light: Luminosity Functions from the New COLIBRE Simulations and the High-Redshift Challenge
Speaker: Shengdong Lu （Durham University）
Abstract：
COLIBRE is a new generation of large-volume cosmological hydrodynamical simulations. For the first time on such large cosmological scales, COLIBRE explicitly and self-consistently models the key physical processes of the multiphase ISM, while following the production, growth, and destruction of interstellar dust. This enables us to construct a calibration-free forward-modelling framework: starting from the simulated galaxy populations and their physical properties, we use the radiative-transfer code SKIRT to predict galaxy emission from the far-ultraviolet to the submillimetre. In this talk, I will first show how this framework successfully reproduces the galaxy luminosity functions in the local Universe over this broad wavelength range, from the far-ultraviolet to the submillimetre. Although there remains room for improvement at mid-infrared wavelengths, the agreement across such a wide spectral range indicates that COLIBRE provides a good description not only of the galaxy population in the nearby Universe, but also of the amount and spatial distribution of dust within galaxies.
I will then apply the same framework to redshifts z=7-15 and compare the results with the latest JWST observations. We find that, despite its success in the local Universe, COLIBRE systematically underpredicts the ultraviolet luminosities of high-redshift galaxies, especially at the bright end and at the highest redshifts. Further analysis shows that neither neglecting dust attenuation nor accounting for observational uncertainties is sufficient to fully explain this discrepancy. This suggests that additional physical mechanisms may be required to enhance the ultraviolet output of early galaxies. Finally, I will present new simulations based on a variable initial mass function (vIMF). In this model, stars formed in higher-density gas have a larger relative contribution from massive stars, thereby increasing the ultraviolet luminosities of high-redshift galaxies. Our preliminary results show that such a vIMF can substantially alleviate, and potentially explain, the discrepancy in the luminosity function at z=15. This provides a promising physical route for understanding the high-redshift bright-galaxy challenge revealed by JWST.
Bio：
Shengdong Lu is currently a postdoctoral researcher at the Institute for Computational Cosmology, Durham University, working with Professor Carlos S. Frenk. He received his bachelor’s degree from the Department of Astronomy at the University of Science and Technology of China, and obtained his PhD in Astrophysics from the National Astronomical Observatories, Chinese Academy of Sciences, in 2020. From 2020 to 2023, he was a postdoctoral researcher in the Department of Astronomy at Tsinghua University. Shengdong’s research interests include galaxy dynamics, galaxy formation and evolution, cosmological simulations, and radiative-transfer modelling. In recent years, his research has shifted towards using a new generation of cosmological simulations to study the multi-wavelength emission properties of galaxies, as well as the formation and evolution of galaxies in the very early Universe. Within the international COLIBRE collaboration, Shengdong leads the research on galaxy luminosity functions. He uses a forward-modelling framework based directly on the physical properties of simulated galaxies to predict their multi-wavelength observational properties, and to test and diagnose the galaxy-formation physics implemented in numerical simulations. His current research focuses on understanding the high-redshift bright-galaxy challenge revealed by JWST, and on exploring the roles of star formation, dust attenuation, and the initial mass function in early galaxies.
Time: 10:30-11:30,21/May, Thursday
Venue: Room 506 (Large seminar room), Department of Astronomy
