Recently, it has been shown that a correlation exists between the rate of shear and the spiral arm pitch angle in disk galaxies. The rate of shear depends upon the shape of the rotation curve, which is dependent upon the mass distribution in spiral galaxies. Here, we present an imporoved correlation between shear rate and spiral arm pitch angle, by increasing the sample size. We also use an adiabatic infall code to show that the rate of shear is most strongly correlated with the central mass concentration, c_m. The spin parameter, $lambda$, and the fraction of baryons that cool, F, cause scatter in this correlation. Limiting this scatter, such that it is equal to that in the correlation between shear rate and pitch angle, and using a value of F=0.1 to 0.2, the spin parameter must be in the range 0.03<lambda<0.09 for spiral galaxies. We also derive an equation which links spiral arm pitch angle directly to c_m.
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