Formation of ob clusters: CO, NH3, and H2O observations of the distant H II region complex in S128

The spectral line emission from the 12CO, 13CO, C18O, and NH3 molecular species was mapped for the molecular cloud surrounding the S128 H II region. The 12CO map shows an elongated cloud (approx. 9 x 3') having at least two cloud components at -74 and -72.8 km s-1. The extent of the CO cloud was searched for H2O maser emission. A further H2O maser was detected close to the compact H II region S128N. All the signposts of star formation, the H II regions, and the H2O maser sources are found to lie along the transition between the -74 km s-1 and -72.8 km s-1 clouds, suggesting that the interaction of these two clouds may have initiated the observed star formation