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Motosuji Fujishita, Kazufumi Torii, Natsuko Kudo, Tokuichi Kawase, Hiroaki Yamamoto, Akiko Kawamura, Norikazu Mizuno, Toshikazu Onishi, Akira Mizuno, Mami Machida, Kunio Takahashi, Satoshi Nozawa, Ryoji Matsumoto, Yasuo Fukui, Discovery of Molecular Loop 3 in the Galactic Center: Evidence for a Positive-Velocity Magnetically Floated Loop towards L= 355|$^\circ$|–359|$^\circ$|, Publications of the Astronomical Society of Japan, Volume 61, Issue 5, 25 October 2009, Pages 1039–1053, https://doi.org/10.1093/pasj/61.5.1039
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Abstract
We have discovered a molecular dome-like feature towards 355|$^{\circ}$||$\leq$||$l$||$\leq$| 359|$^{\circ}$| and 0|$^{\circ}$||$\leq$||$b$||$\leq$| 2|$^{\circ}$|. The large velocity dispersions of 50–100 km s|$^{-1}$| of this feature are much larger than those in the Galactic disk, and indicate that the feature is located in the Galactic center, probably within |$\sim $|1 kpc of Sgr A|$^{\ast}$|. The distribution has a projected length of |$\sim $|600 pc and a height of |$\sim $|300 pc from the Galactic disk, and shows a large-scale monotonic velocity gradient of |$\sim $|130 km s|$^{-1}$| per |$\sim $|600 pc. The feature is also associated with HI gas having a more continuous spatial and velocity distribution than that of |${}^{12}$|CO. We interpret the feature as being a magnetically floated loop similar to loops 1 and 2, and name it “loop 3”. Loop 3 is similar to loops 1 and 2 in its height and length, but is different from loops 1 and 2 in that the inner part of loop 3 is filled with molecular emission. We have identified two foot points at both ends of loop 3. HI, |${}^{12}$|CO, and |${}^{13}$|CO datasets were used to estimate the total mass and the kinetic energy of loop 3 to be |$\sim $|3.0 |$\times$| 10|$^{6} M_\odot$| and |$\sim $|1.7 |$\times$| 10|$^{52} $|erg. The huge size, velocity dispersions, and energy are consistent with the magnetic origin of the Parker instability, as in the case of loops 1 and 2, but is difficult to be explained by multiple stellar explosions. We argue that loop 3 is in an earlier evolutionary phase than loops 1 and 2 based on the inner-filled morphology and the relative weakness of the foot points. This discovery indicates that the western part of the nuclear gas disk of |$\sim $|1 kpc radius is dominated by the three well-developed magnetically floated loops, and suggests that the dynamics of the nuclear gas disk is strongly affected by magnetic instabilities.
