High-Velocity Molecular Gas in the Galactic Center Radio Lobe

We point out a possible association of high-velocity molecular gas with the Galactic Center Radio Lobe (GCL). A molecular spur in the eastern GCL ridge is receding at \Vlsr \sim +100 \kms, and the western spur approaching at \Vlsr \sim -150 \kms, suggesting a high-velocity rotation of the GCL. We study the kinematics of the GCL based on these molecular line data.Comment: To appear in ApJ. Letters, Plain TeX, Figures on reques

Galactic Center Molecular Arms, Ring and Expanding Shells. II - Expanding Molecular Shell -

We investigate the three-dimensional structure of the so-called ``200-pc expanding molecular ring" in the Galactic Center by analyzing (b, Vlsr) diagrams of the 13CO(J=1-0) line emission from the Bell-Telephone Laboratory survey. We show that the b-v features can be fitted by a spheroidal shell pinched at the equator (dumbbell-shaped shell), which we call the expanding molecular shell (EMS). The radius is about 180 pc and the vertical extent is more than +/-50 pc. The shell is expanding at 160 km/s, and is rotating at 70 km/s. The association of the radio continuum emission indicates that the EMS is a mixture of molecular and ionized hydrogen gases. An extended hot (X-ray) plasma appears to fill the interior of the shell. The estimated molecular mass of the shell is approximately 1.E7 Msun and its kinetic energy 2.E54 ergs.Comment: To appear in PASJ vol.47, No.5, 1995, Plain TeX, Figures on reques

Dark Bulge, Exponential Disk, and Massive Halo in the Large Magellanic Cloud

The rotation curve of the Large Magellanic Cloud, which we have derived from high-resolution HI position-velocity diagrams observed by Kim et al (1998), shows a steep central rise and flat rotation with a gradual rise toward the edge. Using the rotation curve, we have calculated the distribution of surface mass density, and show that the LMC has a dark compact bulge, an exponential disk, and a massive halo. The bulge is 1.2 kpc away from the center of the stellar bar, and is not associated with an optical counterpart. This indicates that the "dark bulge" has a large fraction of dark matter, with an anomalously high mass-to-luminosity (M/L) ratio. On the contrary, the stellar bar has a smaller M/L ratio compared to the surrounding regions. (http://www.ioa.s.u-tokyo.ac.jp/~sofue/99lmc.htm)Comment: PASJ 1999 in press, Latex with Postscript figure

Galactic Center Shells and a Recurrent Starburst Model

By applying filtering techniques to remove straight filaments in the 20-cm VLA radio image of the Galactic Center Arc region, we have shown that numerous concentric radio shells of radii 5 to 20 pc are surrounding the Pistol and Sickle region, which we call Galactic Center Shells (GCS). Each shell has thermal energy of the order of $10^{49-50}$ erg. Several CO-line shells are associated, whose kinetic energies are of the order of $10^{49-50}$ erg. Summing up the energies of recognized GCSs, the total energy amounts to $\sim 10^{51}$ erg. The GCSs show an excellent correlation with the FIR shells observed at 16--26 microns with the MSX. We propose a model in which GCSs were produced by recurrent and/or intermittent starbursts in the Pistol area during the last million yr. The most recent burst occurred some $10^5$ years ago, producing an inner round-shaped shell (GCS I); earlier ones a million years ago produced outer shells (GCS II and III), which are more deformed by interactions with the surrounding ISM and Sgr A halo. We argue that recurrent starbursts had also occurred in the past, which produced larger scale hyper shell structures as well. A burst some million years ago produced the Galactic Center Lobe, and a much stronger one 15 million years ago produced the North Polar Spur.Comment: To appear in PASJ, Latex 8 pages, 5 figures, See http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2003gcs/ for original figure