Discovery of the pigtail molecular cloud in the galactic center

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.