Yoshinori Yonekura

The central few hundred parsecs of the Milky Way host a massive black hole and exhibit very violent gas motion and high temperatures in molecular gas. The origin of these properties has been a mystery for the past four decades. Wide-field imaging of the ¹² CO (rotational quantum number J = 1 to 0) 2.6-millimeter spectrum has revealed huge loops of dense molecular gas with strong velocity dispersions in the galactic center. We present a magnetic flotation model to explain that the formation of the loops is due to magnetic buoyancy caused by the Parker instability. The model has the potential to offer a coherent explanation for the origin of the violent motion and extensive heating of the molecular gas in the galactic center.

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 ΔVcomp, radius r, mass M, column density N(H2), and average number density n(H2) were 3.3 km s-1, 2.2 pc, 2.6 × 103 M☉, 1.3 × 1022 cm-2, and 1.2 × 103 cm-3, 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 Mvir/M. We also found that the cores in the η Car GMC are characterized by large ΔV and Mvir/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.

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.