Understanding the Multi-Phase Structure and Physical Conditions of the ISM - A Dominant Reservoir of CO-Dark Molecular Gas in 30 Doradus
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Mélanie Chevance
University of Heidelberg
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Determining the efficiency with which gas is converted into stars in galaxies requires an accurate determination of the total reservoir of molecular gas mass. Despite being the most abundant molecule in the Universe, H2 is challenging to detect through direct observations and indirect methods have to be used to estimate the total molecular gas reservoir. These are generally calibrated in the Milky Way, yet evidence of the environmentally dependence of scaling relations from tracers such as CO or dust are growing. I will present new SOFIA/FIFI-LS observations of the massive star-forming region 30 Doradus in the Large Magellanic Cloud, where the half-solar metallicity gas is strongly irradiated by the central super stellar cluster. In combination with the Meudon photodissociation region model, we have constrained the physical properties and the 3D structure of the gas, and determined the spatially resolved distribution of the total reservoir of molecular gas in the proximity of the super stellar cluster. We find that the strong radiation field combined with the reduced metallicity of the surrounding gas are responsible for a large reservoir of "CO-dark" molecular gas, leaving a large amount of the total H2 gas (>75%) undetected when adopting a standard CO-to-H2 conversion factor in this massive star forming region.

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