More interesting stuff ..
Quote:
Of course, in real galaxies, masses are neither distributed in infinitely thin disks nor in ideally spherically symmetric structures, orbits are not circular, rotation field has a very complicated structure, and mass distribution does not have axial symmetry – axial symmetry is clearly broken by bars and spiral structure.
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The models are only slightly more accurate than would be a dimensional analysis, which states that the amount of electro- magnetic energy radiated by a galaxy should be given by L=αDc Vc2 / (Gμ), where Vc is some characteristic velocity derived from Doppler image, Dc is its radial size estimated based on the spatial range of the luminous stuff, μ is some mass-to-light ratio derived on population analysis ground, and α is some unknown dimensionless factor related to the particular geometry of mass distribution and of rotation field. All parameters apart from α can be estimated from measurements.
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The approximation should improve when one distinguishes spherical and disk-like subcomponents, further, one can add a width to the disk, and so on. But it would be hard to treat these models seriously when dynamics and stability of a galaxy is concerned (especially when maximal disk model is used which treats on equal footing flat and spheroidal internal mass components).
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Without realistic modeling such difficult problems as structural stability, cannot be answered.
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Aside from the Electromagnetic paragraph (only included to show they have a way of modelling it), Carl, I think you've pointed out before, the importance of getting the model right before making any conclusions about Galaxy Rotation Curves. I think Steven may have, also. It certainly is complex and dependent on the shapes of the Galaxies, matter densities etc.
Lots more work to do in this area, it seems.
Cheers