This paper reports the discovery of a helical molecular cloud in the central molecular zone (CMZ) of our Galaxy. This "pigtail" molecular cloud appears at (l, b, V LSR) ≃ (-0°7, + 0°.0, - 70 to -30kms-1), with a spatial size of ∼20 × 20 pc2 and a mass of (2-6) × 105 M⊙. This is the third helical gaseous nebula found in the Galactic center region to date. Line intensity ratios indicate that the pigtail molecular cloud has slightly higher temperature and/or density than the other normal clouds in the CMZ. We also found a high-velocity wing emission near the footpoint of this cloud. We propose a formation model of the pigtail molecular cloud. It might be associated with a magnetic tube that is twisted and coiled because of the interaction between clouds in the innermost x 1 orbit and ones in the outermost x 2 orbit.
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