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Title: Probing cold gas with Lyman-alpha and Mg II radiative transfer

Speaker: Dr. Seok-Jun Chang (MPA)

Date&Time: 2024-04-30, 3:00 PM

Location: Science Hall 638

Talk to be delivered in English
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Abstract: The structure and kinematics of the gas around and in galaxies are crucial for understanding the multiphase flows within the galactic ecosystem and, thus, galaxy evolution and star formation as a whole. Traditionally, insights into the structure of galactic winds and the circumgalactic medium have been investigated through absorption line studies. Recent advancements in instruments and techniques, however, offer a new perspective on gas flows around galaxies through emission lines like Hydrogen Lyman-α (Lyα) and metal resonance lines such as Mg II, C IV, O VI, and N V doublets. The resonant nature of these lines induces photon scattering, imprinting the physical properties of multiphase gas on their observables. To decode information, we developed a 3D Monte-Carlo radiative transfer simulation named 'RT-scat'. During my presentation, I will show simulated results using this code, specifically exploring the radiative transfer of Mg II doublet λλ2795 & 2803 and Lyα, tracing cold gas with temperatures around 10^4 K. Apart from showing synthetic spectra and escaping fractions, in particular, I will focus on the powerful observables that have received less attention in the past: the Lyα polarization signal and the Mg II doublet ratio. I will show how these observables can help to constrain cold gas flows. Time provided, the presentation will also briefly touch upon the broader implications of these findings on resonant doublets tracing warm gas with T ≥  10^5 K, such as C IV, O VI, and N V doublets.