Satellite and ground based observations of massive star forming regions

Doctoral thesis, 2003

Results from submm/mm radio astronomical observations, using the astronomy/-aeronomy satellite Odin and the 20m telescope at the Onsala Space Observatory, are presented. Analysis of spectroscopic data of interstellar rotational emission lines from gaseous H2O residing in giant molecular clouds (GMCs), reveal important new clues about the chemistry and spatial distribution of water molecules in these regions, including estimates of the water abundance in molecular outflows associated with massive star formation. In an extensive study of the DR21 GMC, involving a multitude of molecular lines, it is argued that spatial variations in the emission from a multiply split rotational transition of the cyanogen radical (CN), reflect differences in the excitational context which governs the level populations in the rotational states. It is further argued that this reflects variations in the general physical conditions across the region. Together with observations of hydrogen cyanide (HCN) isotopologues, the CN mapping data are also interpreted to delineate regions of increased photochemical activity. Results from uniquely sensitive Odin searches in a number of different Milky Way molecular clouds, for the 2.5 mm line from the ground state transition of molecular oxygen, have been analysed and used to calculate new, lower upper limits to the interstellar molecular oxygen abundance (all O2 observations yet have resulted in non-detections). A study based on observations of sulphur monoxide (SO) isotopologues indicates that the elemental oxygen isotopic ratio, 16O/18O, is much lower than previously thought in the interior of massive star forming regions, probably as a result of 18O-enriched ejected material from earlier generations of massive stars being returned to and mixed with the local ISM. This result may have implications for analyses relying on observations of other isotopically substituted oxygen bearing molecules, such as H218O and C18O (commonly used to estimate total gas column densities).