Effects of magnetic fields on the stability of a differentially rotating disk are considered in the shearing sheet approximation.An explicit stability criterion is derived in terms of Toomre's Q value and the fiel...Effects of magnetic fields on the stability of a differentially rotating disk are considered in the shearing sheet approximation.An explicit stability criterion is derived in terms of Toomre's Q value and the field strength.The combined effects of both magnetic fields and a corotating dark matter halo are briefly discussed.展开更多
This letter is emphasized on the discussion of the group velocity of disturbed galactic density waves(GDW),which is one of the two most insurmountable problems in the density waves theory.In our calculation,we find th...This letter is emphasized on the discussion of the group velocity of disturbed galactic density waves(GDW),which is one of the two most insurmountable problems in the density waves theory.In our calculation,we find that the galactic thickness has an important effect on the GDW.The dynamic time scale of GDW in our three-dimensional model can be prominently prolonged,from 36%to 60%contrasting to that of two-dimensional galactic model.However,it is still less than the lifetime of our Galaxy,which means that it is necessary to seek some other physical mechanisms to excite and sustain the GDW.展开更多
A new method is presented to determine the thickness of spiral galaxies.Based on the rigorous solution of the Poisson equation for logarithmic density disturbance in three-dimensional spiral galaxies,we have derived a...A new method is presented to determine the thickness of spiral galaxies.Based on the rigorous solution of the Poisson equation for logarithmic density disturbance in three-dimensional spiral galaxies,we have derived an accurate dispersion relation for the stellar and gaseous disk with a finite thickness.From this relation,a new method is put forward here for determining the thickness of galaxies.We apply this way to M31 and get the thickness of about 0.7kpc,which is in good agreement with the previous results.展开更多
基金Supported by the NSC under Grant No.NSC89-2112-M-008-055the National Natural Science Foundation of China under Grant No.G1999075406.
文摘Effects of magnetic fields on the stability of a differentially rotating disk are considered in the shearing sheet approximation.An explicit stability criterion is derived in terms of Toomre's Q value and the field strength.The combined effects of both magnetic fields and a corotating dark matter halo are briefly discussed.
基金Supported in part by the National Natural Science Foundation of China under Grant No.19873005the Director Foundation of National Education Ministry(9528424)the National Climbing Project on Fundamental Researches.
文摘This letter is emphasized on the discussion of the group velocity of disturbed galactic density waves(GDW),which is one of the two most insurmountable problems in the density waves theory.In our calculation,we find that the galactic thickness has an important effect on the GDW.The dynamic time scale of GDW in our three-dimensional model can be prominently prolonged,from 36%to 60%contrasting to that of two-dimensional galactic model.However,it is still less than the lifetime of our Galaxy,which means that it is necessary to seek some other physical mechanisms to excite and sustain the GDW.
基金Supported in part by the National Natural Science Foundation of China under Grant No.19873005the Director Foundation of National Education Ministry(9528424)the National Climbing Project on Fundamental Researches.
文摘A new method is presented to determine the thickness of spiral galaxies.Based on the rigorous solution of the Poisson equation for logarithmic density disturbance in three-dimensional spiral galaxies,we have derived an accurate dispersion relation for the stellar and gaseous disk with a finite thickness.From this relation,a new method is put forward here for determining the thickness of galaxies.We apply this way to M31 and get the thickness of about 0.7kpc,which is in good agreement with the previous results.
