Volume 26, April 2007 - Meeting Summaries

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International GC Research and Meetings

Galactic Center Mini-workshop

A Galactic center mini-workshop was held at NAOJ, on 2006 July 6. This meeting focused on the semicircular structures of the molecular gas found in the Galactic center. Summarised by the conference organiser, Mami Machida.

1. Part 1: Discovery of Molecular Loops in the Galactic Center
   • Molecular Loops in the Galactic Center They presented a magnetic floatation model in which molecular loops discovered by the NANTEN telescope are formed due to the magnetic buoyancy caused by the Parker instability. (Fukui, Yasuo, Nagoya Univ.)
   • Molecular Loops--Detailed Discussion They discussed about the forth quadrant loops: Loop 1 and 2. The kinetic energy involved in a loop is estimated to be 10⁵¹ erg for a velocity dispersion of 30 km s^-1. The position-velocity diagram showed that loop foot points have a large velocity span and are connected by a bridge. (Kudo, Natsuko, Nagoya Univ.)
   • Molecular Loops--Comparison with CO and HI They compared the distribution of CO with HI gas in Loop 1 and 2. They found a good correlation between CO and HI. (Torii, Kazufumi, Nagoya Univ.)
2. Part 2: Observations at Other Wavelengths
   • Vertical Structure in Edge-on Galaxy NGC 891 They found that a prominent spur structure of molecular gas is emerging vertically from the disk in NGC 891. They suggested that this spur may be ejected from the Galactic disk due to a superbubble or formed by the Parker instability. (Handa, Toshihiro, Univ. of Tokyo)
   • High Excitation Molecular Gas in CMZ They discovered a vast amount of high-temperature and low-density gas with a large velocity dispersion in the central molecular zone of the Galaxy. These high excitation gas and wide velocity dispersion indicate that local expansions are the origin of compact molecular gas structures. (Oka, Tomoharu, Univ. of Tokyo)
   • Magnetic Field Structure of SNRs Supernova remnants (SNRs) are one of the efficient accelerators of cosmic rays. Hard X-ray observations show that the acceleration efficiency at shock fronts of SNRs is very high. From TeV gamma-ray observations, they suggested that a few hundred undiscovered SNRs may exist. (Bamba, Aya, RIKEN)
   • Magnetic Field in the CMZ According to the infrared observations, the magnetic field in the Galaxy is aligned with the Galactic plane. In the CMZ, the magnetic field strength is estimated to be milligauss. (Nakagawa, Takao, JAXA)
3. Part 3: Theories and Numerical Simulations of the Parker Instability
   • Origin of Molecular Loop Structures They considered that molecular loop structures are created by the Parker instability. If the strength of the magnetic field is about 100 mu G, the molecular gas sliding down along the magnetic fields can generate velocity dispersion of as high as 50 km s^-1. (Matsumoto, Ryoji, Chiba Univ.)
   • Two-dimensional Simulations of Galactic Loops They carried out two-dimensional MHD simulations of the Parker instability. It successfully reproduced the two loop-like structures observed in the Galactic center region. (Nozawa, Satoshi, Ibaraki Univ.)
   • Three-dimensional Simulations of Galactic Disks They carried out three-dimensional MHD simulations of Galactic gas disks. They showed that the magnetic flux buoyantly rise from the disk. (Machida, Mami, NAOJ)
4. Part 4: Theories of the Phenomenon in Galactic Disks
   • Magnetic Field Amplification Due to the Galactic rotation, the Galactic gas disk subjects to MRI and becomes turbulent. When the gas is isothermal, magnetic flux tubes can be created. (Sano, Takayoshi, Osaka Univ.)
   • Formation of Molecular Gas Cloud They studied the conditions for the molecular cloud formation by the Parker instability. (Koyama, Hiroshi, Kobe Univ.)
   • Particle Acceleration inside the Galaxy They investigated whether the shock formed by the Parker instability can be the origin of the particle acceleration for the energy range between 10¹⁵ and 10¹⁸ eV or not. They concluded from the rough estimation that the Parker instability is likely to be the origin of cosmic-ray acceleration. (Asano, Katsuaki, NAOJ)

American Astronomical Society Meeting

1. Sgr A*
   • ``Flaring Activity of Sgr A*: Adiabatic Expansion of Nonthermal Plasma,'' F. Yusef-Zadeh et al. (112.07)
   • ``Hypervelocity Stars Ejected from the Galactic Center,'' W. R. Brown (138.01)
   • ``Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center,'' M. P. Muno et al. (254.10)
2. The Galactic Center Environment
   • ``The Galactic Center: High-resolution Imaging and Temperature Determination of Dense Molecular Clouds,'' J. Ott et al. (017.11)
   • ``Comparison of ¹³CO Line and Far-Infrared Continuum as a Diagnostic of Dust and Molecular Gas Physical Conditions--Implications for the N(H₂)/I(CO) Conversion Factor,'' W. F. Wall (055.01)
   • ``A Wide Area Map of The Galactic Center at 1.1 mm,'' E. A. Mills et al. (172.01)
   • ``Modeling the Galactic Center Magnetic Field Using Synchrotron Flux Density Ma ps,'' B. J. Cowin & M. Morris (172.02)
   • ``A High-resolution Polarimetric Survey of the Central 200 pc of the Galaxy,'' T. M. Freismuth et al. (172.16)
   • ``An HI Absorption Survey of the Central 250 pc of the Galactic Center: Distance Constraints & Understanding the Complex ISM,'' K. I. Clubb & C. C. Lang (172.24)
3. Stars in the Galactic Center
   • ``High Resolution Radio Observations of the Nebulae of Luminous Blue Variable Stars,'' A. Mercer et al. (101.05)
   • ``First Results from a Galactic Center Search for Pulsars and Transients:A Rotating Radio Transient Candidate,'' J. S. Deneva et al. (159.08)
   • ``New Hot Stars in the Galactic Center,'' J. Mauerhan (172.03)
   • ``Spectroscopic Observations of the Galactic Center with OSIRIS,'' T. Do et al. (172.25)
   • ``The Proper Motion of the Arches Cluster: Cluster Membership and Understanding the Origin of Massive Young Clusters near the Galactic Center,'' A. Stolte et al. (254.06)
4. Extreme Physics in the Galactic Center
   • ``The Search for Dark Matter and New Physics using the Gamma Ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT),'' L. L. Wai et al. (037.01)
   • ``Gamma-rays from Dark Matter in the Galactic Center,'' D. P. Finkbeiner (037.0 2)
5. Astrometry in the Galactic Center
   • ``43 GHz SiO Masers for Phase Calibration with VERA in the Galactic Center,'' R. M. Edmonds et al. (172.07)
   • ``Gravitational Lensing and the Distance to the Galactic Center,'' E. L. Gutbrod & S. Levine (172.12)