High‐Mass Cloud Cores in the η Carinae Giant Molecular Cloud

We carried out an unbiased survey for massive dense cores in the giant molecular cloud associated with eta Carinae with the NANTEN telescope in 12CO, 13CO, and C18O 1-0 emission lines. We identified 15 C18O cores. Two of the 15 cores are associated with IRAS point sources whose luminosities are larger than 10^4 Lo, which indicates that massive star formation is occuring within these cores. Five cores including the two with IRAS sources are associated with MSX point sources. We detected H13CO+ (1-0) emission toward 4 C18O cores, one of which is associated with neither IRAS nor MSX point sources. This core shows the presence of a bipolar molecular outflow in 12CO (2-1), which indicates that star formation is also occuring in the core. In total, six C18O cores out of 15 are experienced star formation, and at least 2 of 15 are massive-star forming cores in the eta Car GMC. We found that massive star formation occurs preferentially in cores with larger column density, mass, number density, and smaller ratio of virial mass to LTE mass Mvir/M. We also found that the cores in the eta Car GMC are characterized by large line width and Mvir/M on average compared to the cores in other GMCs. We investigated the origin of a large amount of turbulence in the eta Car GMC. We propose the possibility that the large turbulence was pre-existing when the GMC was formed, and is now dissipating. Mechanisms such as multiple supernova explosions in the Carina flare supershell may have contributed to form a GMC with a large amount of turbulence.