Testing Baryonic Cycling: Star Formation, Feedback, Environment, and Structure in Nearby Galaxies

Wednesday 14 Oct 2026, 14:00 → 15:00 Asia/Shanghai

Tsung-Dao Lee Institute/S4F-SW - Open Area (Tsung-Dao Lee Institute)

Hassen Yesuf

Title: Testing Baryonic Cycling: Star Formation, Feedback, Environment, and Structure in Nearby Galaxies
Time: 14:00-15:00 (UTC+8), 14 October 2026, Wednesday
Host: Darius Modirrousta-Galian
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Meeting ID: 450750540 (no password)

Abstract:
Galaxy evolution is governed by processes spanning an enormous range of scales, from supermassive black hole growth and feedback to gas accretion, star formation, and dark matter halo assembly. In this talk, I test galaxy evolution models from three perspectives: galaxy populations, internal structure, and the baryon cycle. First, I highlight an analysis of ~60,000 nearby active galactic nuclei (AGNs), alongside new environmental and halo mass measurements for AGN and non-AGN galaxies. Comparisons with the SIMBA, IllustrisTNG, and EAGLE simulations reveal major discrepancies in the connections among star formation, black hole demographics, environment, and halo mass. The simulations overproduce quenched low-mass satellites in massive halos and fail to reproduce the quiescent fractions and AGN demographics of massive central galaxies and galaxies in low-density environments. Second, I compare Subaru HSC observations with mock images from the same simulations using a novel statistic, structural abundance functions (SAFs), revealing a “structural abundance crisis” across multiple galaxy structural indices. Finally, I highlight new DESI results probing the baryon cycle through spectroscopy of ~30,000 galaxies. We identify cold gas inflows in ~20% and outflows in ~7% of galaxies. Surprisingly, inflows are most common in quiescent galaxies, whereas star-forming galaxies are dominated by gravitationally bound outflows. Flow states are more strongly linked to stellar population age and recent evolutionary history than to present-day mass, environment, or structure. These findings suggest two regimes of baryonic cycling: rapid outflow recycling through galactic fountains in star-forming galaxies and persistent, low-level “drizzling” inflows of metal-enriched gas in quiescent systems, potentially sustained by halo cooling. Together, these results reveal key tensions between observations and simulations and constrain the physical processes governing galaxy evolution.

Biography:
Hassen Yesuf is an Associate Researcher at the Shanghai Astronomical Observatory, CAS. He was a Kavli IPMU–KIAA Postdoctoral Fellow (2018–2023) and a postdoctoral researcher at the University of California, Santa Cruz, where he earned his PhD in Astrophysics and Statistics in 2016, following a bachelor’s degree in Astrophysical Sciences from Princeton University. His research aims to understand how galaxies evolve by combining large spectroscopic and imaging surveys, advanced statistical and machine-learning methods, and cosmological simulations to uncover the physical processes driving galaxy evolution. His recent work focuses on the spatiotemporal analysis of the baryon cycle in galaxies.