Contributed Talk - Splinter SOFIA

Tuesday, 12 September 2023, 15:30   (H 3006)

The formation and physical conditions of molecular clods revealed by the [CII], CO and HI lines.

Slawa Kabanovic, Nicola Schneider and the FEEDBACK consortium
I. Physikalisches Institut, Universität zu Köln

The assembly and structure of molecular clouds (H2) out of atomic gas flows and the subsequent formation of dense structures, which are birth places of stars, is one of the main topics in astrophysics. Resent analysis of the [CII] line in combination with the CO and HI emission allowed us to better asses stellar feedback and cloud and star formation processes. We here present the results of combining spectroscopic observations of carbon monoxide (CO), ionized carbon ([CII]), and atomic hydrogen (HI) in massive star-forming regions such as Orion A and Cygnus X. These two regions are the largest [CII] existing maps which were observed with heterodyne receiver upGREAT on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). [CII] data from the SOFIA legacy project FEEDBACK in Cygnus X revealed the highly dynamic interaction of CO-dark gas in the form of atomic flows with a small molecular fraction and shed light on the molecular cloud formation process (Schneider et al. 2023). In addition, we discovered in all FEEDBACK sources expanding bubbles seen in the [CII] line. However, the role and the driving mechanism of this fast expanding [CII] shells (e.g., Luisi et al. 2021, Bonne et al. 2022, Beuther et al. 2022) are not yet fully understood. With the help of a multi-layer radiative transfer model for CO and [CII] emission, combined with HI self-absorption (HISA) studies, we showed for the RCW 120 HII bubble that the associated molecular cloud is flat, probably emerging from a relic filament (Kabanovic et al. 2022). The large amount of observed cold [CII] arises from an HI envelope, with similar physical condition as the atomic gas flows in Cygnus X. As part of the Orion Legacy project (PI S. Kabanovic) multiple longtime integrations across Orion A were performed observing weak [13CII] transition lines. These observations allow us to determine the local [12CII]/ [13CII] abundance ration directly for the first time across different physical conditions in Orion A tracing possible fractionation effects. In addition, the longtime integrations allow to study the spatial distribution of the [13CII] isotope and utilizing the two-layer multicomponent model the spatial distribution of the cold atomic gas. Beuther H., Schneider N., Simon R., et al., 2022, A&A, 659, 77 Bonne L., Schneider N., Garcia, P., et al., 2022, ApJ, 935, 171 Kabanovic S., Schneider N., Ossenkopf-Okada V., et al., 2022, A&A, 659 Luisi M., Anderson A., Schneider N., Simon R., Kabanovic S., et al., 2021, Science Advances, 9, Vol. 7 Schneider N., Bonne L., Bontemps S., Kabanovic S., et al., 2023, Nature Astronomy, 7, 546