2005ApJ...634..476Y

We carried out an unbiased survey for massive dense cores in the giant molecular cloud associated with η Carinae with the NANTEN telescope in the ¹²CO, ¹³CO, and C¹⁸O J=1-0 emission lines. We identified 15 C¹⁸O cores, whose typical line width ΔV_comp, radius r, mass M, column density N(H₂), and average number density n(H₂) were 3.3 km/s, 2.2 pc, 2.6x10³ M_☉, 1.3x10²²/cm2, and 1.2x10³/cm3, respectively. Two of the 15 cores are associated with IRAS point sources whose luminosities are larger than 10⁴ L_☉, which indicates that massive star formation is occurring within these cores. Five cores, including the two with IRAS sources, are associated with MSX point sources. We detected H¹³CO⁺ (J=1-0) emission toward four C¹⁸O cores, two of which are associated with IRAS and MSX point sources; another one is associated only with an MSX point source, and the other is associated with neither IRAS nor MSX point sources. The core with neither IRAS nor MSX point sources shows the presence of a bipolar molecular outflow in ¹²CO (J=2-1), which indicates that star formation is also occurring in the core, and the other three of the four H¹³CO⁺ detections show winglike emission. In total, 6 C¹⁸O cores out of 15 (=40%) have experienced star formation, and at least 2 of 15 (=13%) are massive star-forming cores in the η Car GMC. We found that massive star formation occurs preferentially in cores with larger N(H₂), M, and n(H₂) and a smaller ratio of M_vir/M. We also found that the cores in the η Car GMC are characterized by large ΔV and M_vir/M on average compared to the cores in other GMCs observed with the same telescope. These properties of the cores may account for the fact that as much as 60%-87% of the cores do not show any signs of massive star formation. We investigated the origin of a large amount of turbulence in the η Car GMC. We found that turbulence injection from stellar winds, molecular outflows, and supernova remnants that originated from stars formed within the GMC are not enough to explain the existing turbulence. We propose the possibility that the large turbulence was preexisting 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.