| Temperature and Density in the Foot Points of the Molecular Loops in the Galactic Center; Analysis of Multi-J Transitions of 12CO(J=1-0, 3-2, 4-3, 7-6), 13CO(J=1-0) and C18O(J=1-0) (2009) | |||||||||
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Abstract | |||||||||
| Fukui et al. (2006) discovered two molecular loops in the Galactic center and argued that the foot points of the molecular loops, two bright spots at the both loop ends, represent the gas accumulated by the falling motion along the loops, subsequent to the magnetic flotation by the Parker instability. We have carried out sensitive CO observations of the foot points toward l = 356 deg. at a few pc resolution in the six rotational transitions of CO; 12CO(J=1-0, 3-2, 4-3, 7-6), 13CO(J=1-0) and C18O(J=1-0). The high resolution image of 12CO(J=3-2) has revealed detailed distribution of the high excitation gas including a U shape, the outer boundary of which shows sharp intensity jumps accompanying strong velocity gradients. An analysis of the multi-J CO transitions shows that temperature is in a range from 30 - 100 K or higher and density is around 10^3 - 10^4 /cm^3, confirming that the foot points have high temperature and density although there is no radiative heat source like high mass stars in and around the loops. We argue that the high temperature is likely due to the shock heating under C-shock condition caused by the magnetic flotation. We made a detailed comparison of the distribution obtained with theoretical numerical simulations and note that the U shape seems to be consistent with numerical simulations. We also find that the region of highest temperature of 60 K or higher inside the U shape corresponds to the spur having upward flow, additionally heated up either by magnetic reconnection or bouncing in the interaction with the narrow "neck" at the bottom of the U shape. We note these new findings further reinforce the magnetic floatation interpretation.. Comment: 36 pages, 17 figures, submitted to PASJ | |||||||||
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