Abstract

Contributed Talk - Splinter Galaxies

Friday, 11 September 2026, 17:00   (MW-0250)

Probing Cold Gas within and around Galaxies through the Mg II Resonance Doublet

Seok-Jun Chang, Max Gronke
Max Planck Institute for Astrophysics

The structure and kinematics of gas in and around galaxies encode the multiphase flows that drive galaxy evolution and star formation. Resonance emission lines, Hydrogen Lyman-α and metal transitions such as Mg II, C IV, O VI, and N V, offer a powerful window into these circumgalactic flows, with the Mg II λλ2796,2803 doublet emerging as a promising tracer of cold gas at T ~ 10^4 K. To interpret Mg II doublet emission, I developed a 3D Monte Carlo radiative transfer code, RT-scat. In this talk, I will present simulated results showing how Mg II line profiles and the doublet ratio respond to gas geometry and kinematics, inflowing/outflowing, smooth/clumpy, and dusty media, establishing the doublet ratio as a powerful diagnostic of gas flows. I will then present our radiative transfer modeling of Mg II emission halos around star-forming galaxies at z ~ 1 from the MAGG and MUDF surveys, where we find evidence for anisotropic cold gas, alongside evidence for slowly moving or outflowing cold gas. If time allows, I will discuss extensions to other metal resonance lines as multiphase gas tracers.