Accretion and outflow in massive star formation: Observational studies at high angular resolution

This thesis examines the process of massive star formation by observations of the molecular gas surrounding young H II regions at the highest angular resolution. Because the regions that form massive stars are more complicated and more distant than low-mass-star forming regions, high angular resolution is essential. We achieve this resolution through the use of radio interferometry. While an evolutionary sequence for the formation of isolated low-mass stars has been well established over the last decade, a unified picture of massive-star formation remains elusive. Fundamental questions about the nature of accretion in massive star formation, and the chronology of different observed stages remain. We present several pieces of this slowly coalescing picture. First, we show in the case of W51, that high mass star formation can occur roughly coevally over a 1 pc size scale, without being part of a single gravitational collapse. Second, we present observations of a bipolar outflow coincident with an expanding UCH II region, G5.89-0.39. Because bipolar outflows are generally thought to be a signpost of ongoing accretion, and because the spherical expansion of the UCH II region must mean that actual accretion must have stopped, the source presented a mystery. This source shows strong evidence for the compressed time-scales and chronology involved in massive star formation. Third, a clear case can be made for the existence of disks around young massive stars. These disks are different in character than the accretion disks around low mass protostars, being much more massive relative to the central object, and not always rotationally supported. We show observations of such a disk in G28.20-0.05, seen at higher resolution than in any previous work. Fourth, we present observations of a group of young stars in G10.62-0.38, forming in a single gravitational potential. Because massive stars form in clusters, it is understood that the formation of a massive star can effect the formation of surrounding protostars. We show that the existence of massive young stars can also effect their own accretion process, leading to a new physical regime in which both molecular gas and ionized gas are part of a single accretion flow.