ONLINE-COLLOQUIUM: Daniel Seifried (Universität zu Köln)
Wann: Mi, 08.12.2021, 14:00 Uhr
Wo: Zoom link see above
Molecular clouds observed with the HI 21 cm line: are they molecular or atomic?
I present synthetic HI 21 cm line maps of simulated molecular clouds (MCs) within the SILCC-Zoom project. The simulations include a detailed chemical network for H and H2. For direct comparison with actual observations I include realistic observational effects and focus on frequently observed HI self-absorption features towards MCs. I will show that high HI column densities (> 10^22 cm^-2) are frequently reached in MCs and discuss why actual observations, but also 1D-PDR models, might underestimate such column densities and thus the real HI content in MCs. This can be attributed to a combination of different effects. The combination of these effects leads to the fact that the HI content in MCs might be a factor of a few higher than observed, which I back up by recent THOR observations. Using the self-consistent synthetic HI maps, I show that MCs reach HI optical depths of 1 - 10 making optical depth corrections crucial. Finally, I discuss the accuracy with which HI observations can probe the dynamics of the HI gas.