A research team of the Department of Physics, Keio University, has discovered a molecular cloud with a peculiar helical structure by observation with the NRO 45m Telescope at Nobeyama Radio Observatory (NAOJ), National Astronomical Observatory of Japan. The team led by Shinji Matsumura, a second year Ph. D. candidate, and Tomoharu Oka, an Associate Professor, named it a "pigtail" molecular cloud from its morphology. The "pigtail" molecular cloud is located in the Galactic center, approximately 30,000 light years away from the solar system. Giant molecular clouds in this region are orbit around the Galactic center along two closed orbits. At the bottom of the pigtail molecular cloud, these two orbits intersect. The research team analysed multiple molecular spectral lines in detail. The researchers have revealed that the two giant molecular clouds collide with one another at exactly the bottom of the "pigtail" molecular cloud. These findings suggest that the helical structure of the "pigtail" molecular cloud formed when the two molecular clouds with different orbits frictionally collided and the magnetic tube was twisted. Read more
Title: Discovery of the Pigtail Molecular Cloud in the Galactic Center Authors: Shinji Matsumura, Tomoharu Oka, Kunihiko Tanaka, Makoto Nagai, Kazuhisa Kamegai, Tetsuo Hasegawa
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) ~ (-0.7deg, +0.0deg, -70 to -30 km/s), with a spatial size of ~ (20 pc)^2 and a mass of (2-6) 10^5 solar masses. 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.