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Title: Roles of the cold neutral medium in the formation and evolution of molecular clouds

Speaker: Dr. Min-Young Lee (KASI/UST)

Date&Time: 2024-12-06, 11:00 AM

Location: Science Hall B102

Talk to be delivered in English

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Abstract: The transition from HI to H2 is one of the major bottleneck processes toward star formation. Among the two flavors of HI, the cold and warm neutral medium (CNM and WNM), the CNM most likely plays a critical role thanks to its higher density and lower temperature. Despite its expected importance for the HI-to-H2 transition and ensuing star formation, however, the CNM in and around molecular clouds remains largely unexplored due to the difficulty in direct measurements. In this talk, we present two recent studies on the CNM in the solar neighborhood and 30 Doradus (most active star-forming region in the Local Group of galaxies). In the first study, we derived the properties of the CNM (e.g., optical depth, spin temperature, and column density) along 58 individual lines of sight based on HI emission and absorption spectra and examined the CNM conditions for the formation of CO-traced molecular gas. In the second study, we extended our analyses to an extreme star-forming environment and focused on the spatial variations in the properties of the CNM. These studies provide an unprecedented view on the CNM in and around molecular clouds, shedding light on the roles of the CNM in the formation and evolution of molecular clouds.