Geometry of S235 resolved from SOFIA observations of ionized carbon
Velocity-resolved observations of ionized carbon in the HII-region S235 show that, although most of the radiation comes from the direction of ionized hydrogen, it has a different velocity than the ionized hydrogen. Practically the emission does not come from the same gas, but from photon-dominated dense gas behind the HII region.
https://arxiv.org/pdf/1904.12029.pdf (accepted by ApJ)
