The assembly and dispersal of dense gas in star forming regions
Speaker: Lars Bonne
Abstract:
First, I will present work analyzing multiple spectral lines toward low- and high-mass star forming regions. The study employs archival HI data, CO observations from the NANTEN2, APEX, and IRAM 30m observatories, and [CII] observations with the SOFIA telescope. In these regions we demonstrated the presence of recurring organized velocity fields, also found by other authors, which suggests that star formation is initiated by the same mechanism. Namely, magnetic field bending in high-velocity (>7 km/s) colliding flows. This appears to be consistent with magnetic field observations in several nearby clouds, which suggests that the proposed scenario might be widespread and explain both low- and high-mass star formation.
In the second part, I will present observations of the [CII] spectral line by the FEEDBACK legacy program toward ~10 ionized (HII) regions surrounding massive O stars. [CII] is the main coolant of the neutral ISM in photodissociation regions (PDRs) and thus an excellent probe to study the effect of stellar feedback on the host molecular cloud. The [CII] emission reveals previously undetected high-velocity gas (10-20 km/s) in all regions. This high-velocity gas is the result of expanding bubbles and continuous mass ejection in flattened molecular clouds. The detection of this high-velocity gas has reignited the discussion whether radiation or stellar winds drive molecular dispersal. Quantifying the mass ejection rates also allows us to make a direct estimate of molecular cloud dispersal timescales which consistently points to a few (< 5) Myr. This provides direct observational evidence that molecular cloud are transient structures and not in quasi-static equilibrium.