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Paper IPM / Astronomy / 14115  


Abstract:  
We find the dispersion relation for tightly wound spiral density waves in the surface of rotating, selfgravitating disks in the framework of Modified Gravity (MOG). Also, the Toomrelike stability criterion for differentially rotating disks has been derived for both fluid and stellar disks. More specifically, the stability criterion can be expressed in terms of a matter density threshold over which the instability occurs. In other words the local stability criterion can be written as S0 < Scrit (vs, k, a, Î¼0 ), where Scrit is a function of vs (sound speed), Îº (epicycle frequency) and Î± and Î¼0 are the free parameters of the theory. In the case of a stellar disk the radial velocity dispersion sr appears in Scrit instead of vs. We find the exact form of the function Scrit for both stellar and fluid selfgravitating disks. Also, we use a subsample of THINGS catalog of spiral galaxies in order to compare the local stability criteria. In this perspective, we have compared MOG with Newtonian gravity and investigated the possible
and detectable differences between these theories.
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