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  • Gas inflow patterns and nuclear rings in barred galaxies

     

    Seminar Title 

    Gas inflow patterns and nuclear rings in barred galaxies

       

    Speaker:  

    Prof. Juntai Shen 

       

     Affiliation:   

      (Shanghai Astronomical Observatory, CAS)

       
    When Tuesday afternoon , June 9 , 14:30 p.m
       

    Where:  

     Room 619 , Office Block, 2 West Beijing Road (PMO, CAS)
     
     

                             Welcome to Attend  

     
      ( PMO Academic Committee & Academic Circulating committee)
     

    Abstract      

       Star formation is still a mystery. Gravity alone is not able to explain the low star-formation efficiency (~10%) in molecular clouds. While the main-stream models agree on that turbulence can help to support a cloud against self-gravity, the role played by magnetic fields is very controversial. The recent multi-scale observation of cloud magnetic fields in NGC 6334 sheds light on the debate. The field direction does not change significantly from 100 to 0.01 pc, implying that the field is dynamically important compared to gravity and turbulence. In turn, the cloud fragmentation is channeled by the field and self-similar: at multi-scales, elongated cloud structures tend to be perpendicular to the field, which is symmetrically pinched at the ends of cloud elongations. Moreover, the field strength is proportional to the 0.4-power of the density, which is an evidence that the gravitational contraction is channeled by the magnetic field.

       Nuclear rings, dust lanes, and nuclear spirals are common structures in the inner region of barred galaxies, with their shapes and properties linked to the physical parameters of the galaxies. We use high-resolution hydrodynamical simulations to study gas inflow patterns in barred galaxies, with special attention on the nuclear rings. The location and thickness of nuclear rings are tightly correlated with galactic properties, such as the bar pattern speed and bulge central density, within certain ranges. We identify the backbone of nuclear rings with a major orbital family of bars. The rings form exactly at the radius where the residual angular momentum of inflowing gas balances the centrifugal force. We propose a new simple method to predict the bar pattern speed for barred galaxies possessing a nuclear ring, without actually doing simulations. We apply this method to some real galaxies and find that our predicted bar pattern speed compare reasonably well with other estimates. Our study may have important implications for using nuclear rings to measure the parameters of real barred galaxies with detailed gas kinematics. I will also discuss the preliminary results of extending current hydrodynamical simulations to the Milky Way. 

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