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Fukui et al. (2006) discovered two molecular loops in the Galactic center andargued that the foot points of the molecular loops, two bright spots at bothloops ends, represent the gas accumulated by the falling motion along theloops, subsequent to magnetic flotation by the Parker instability. We havecarried out sensitive CO observations of the foot points toward l=356 deg at afew 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 the detailed distribution of the high excitation gasincluding U shapes, the outer boundary of which shows sharp intensity jumpsaccompanying strong velocity gradients. An analysis of the multi-J COtransitions shows that the temperature is in a range from 30-100 K and densityis around 10^3-10^4 cm^-3, confirming that the foot points have hightemperature and density although there is no prominent radiative heating sourcesuch as high mass stars in or around the loops. We argue that the hightemperature is likely due to the shock heating under C-shock condition causedby the magnetic flotation. We made a comparison of the gas distribution withtheoretical numerical simulations and note that the U shape is consistent withnumerical simulations. We also find that the region of highest temperature of~100 K or higher inside the U shape corresponds to the spur having an upwardflow, additionally heated up either by magnetic reconnection or bouncing in theinteraction with the narrow neck at the bottom of the U shape. We note thesenew findings further reinforce the magnetic floatation interpretation.

publications of the astronomical society of japan

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)