The Silver Lining of Galactic Cirrus: From Foreground Nuisance to a New Probe of the Diffuse ISM

Thursday 5 Nov 2026, 10:30 → 11:30 Asia/Shanghai

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

Qing Liu（刘青）

Title: The Silver Lining of Galactic Cirrus: From Foreground Nuisance to a New Probe of the Diffuse ISM
Time: 10:30-11:30 (UTC+8), 5 November 2026, Thursday
Host: Xianzhong Zheng
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Meeting ID: 389661963 (no password)

Abstract: 
The faint, diffuse universe remains largely unexplored. Many interesting phenomena such as stellar halos, tidal debris and intracluster light (ICL), which record how galaxies and clusters assemble, await detailed mapping. Below a surface brightness of 30 mag/arcsec², however, a large fraction of the sky turns out to be “cloudy”: Galactic cirrus, the glow of Milky Way starlight scattered by interstellar dust, can mimic or obscure those extragalactic emission. Yet the complex morphology of cirrus offers a novel view of the diffuse interstellar medium (ISM). I will show how structural analysis of cirrus reveals coherent filaments with scale-free statistics across different ISM tracers, reflecting the interplay of turbulence, magnetic fields, and thermal processes in the diffuse ISM. I will present a statistical method based on these analyses that combines the multiscale cirrus structure with far-infrared dust maps to reconstruct the optical Galactic foreground. I will show its application to the galaxy cluster Abell 2390 imaged by the Euclid Space Telescope, where foreground removal greatly reduces the bias and uncertainties of ICL measurements, and discuss implications about its assembly history. The two roles of cirrus are not independent: understanding the properties of cirrus yields better foreground models for extragalactic light, while deep imaging surveys provide high-resolution images probing ISM physics.

Bio:
Qing Liu is currently an Oort Postdoctoral Fellow at Leiden Observatory in the Netherlands. He obtained his Ph.D. from the University of Toronto in 2024 and a B.S. from the University of Science and Technology of China in 2018. His research interests focus on low surface brightness emission including diffuse galaxies, intracluster light, and diffuse Galactic light, using data from Euclid, CFHT, Herschel, Planck and the Dragonfly Telescope. He is a member of the Local Universe science working group of the Euclid Consortium and a member of the ESA ARRAKIHS mission.