活动
【DoA Colloquium】June 23rd by Hassen Mohammed Yesef (SHAO)
Description
Title: A Multi-scale Crisis in Galaxy Simulations: Connecting Star-formation, Feedback, Environment, and Structure
Speaker: Hassen Mohammed Yesef (SHAO)
Abstract：
Galaxy formation is governed by coupled processes spanning an enormous range of physical scales, from supermassive black hole growth and feedback to gas accretion, star formation, and the assembly of dark matter halos. Yet it remains unclear whether current cosmological simulations can simultaneously reproduce the observed demographics, environments, and internal structures of nearby galaxies. In this seminar, I will first present a comprehensive analysis of ~60,000 nearby AGNs (z < 0.15), combined with new environmental and halo-mass estimates for ~500,000 AGN and non-AGN host galaxies. This dataset enables a unified comparison with leading cosmological simulations: IllustrisTNG, EAGLE, and SIMBA, revealing major tensions between models and observations in the joint distributions of star formation, AGN activity, stellar mass, and halo mass. Although the simulations qualitatively reproduce some broad trends, they systematically fail to capture key aspects of galaxy quenching and AGN demographics across both central and satellite populations. I will then present complementary results based on the internal structure of galaxies. Using a newly developed structural abundance function (SAF) statistic, I compare Subaru Hyper Suprime-Cam observations with matched mock images from the three simulations using a consistent, like-for-like imaging pipeline. The comparison reveals a pronounced “structural abundance crisis”: across multiple structural parameters, the simulations exhibit large and systematic discrepancies, often by factors of several. Together, these results show that state-of-the-art simulations still struggle to reproduce the fundamental properties of nearby galaxies, highlighting the need for improved physical descriptions of baryon cycling, angular momentum redistribution, and the coupling of feedback across the interstellar and circumgalactic media.
Bio:
Prof. Hassen Mohammed Yesef is an Associate Researcher at the Shanghai Astronomical Observatory, Chinese Academy of Sciences (CAS). He was a Kavli IPMU–KIAA Postdoctoral Fellow from 2018 to 2023. He received his PhD in Astrophysics and Statistics from the University of California, Santa Cruz in 2016, and remained there as a researcher until 2018. He obtained his Bachelor’s degree in Astrophysical Sciences from Princeton University. His research focuses on galaxy evolution, including star formation, active galactic nuclei (AGN) feedback, and the interstellar and circumgalactic gas cycle. He also applies statistical and machine learning methods to astrophysical data, with the goal of extracting physical insights from complex galaxy populations.
Time: 14:00-15:00, 23/June, Tuesday
Venue: Room 506 (Large seminar room), Department of Astronomy
Venue: Room 506 (Large seminar room), Department of Astronomy
You can also access the colloquium via: https://www.koushare.com/space/329883/live
