Rotation curve spiral galaxies

The second is using the Tully-Fisher relationship, which provides a direct relationship between the absolute luminosity of a spiral galaxy and its maximum rotation speed. Since the maximum rotation speed can be directly estimated by observation, one can estimate the absolute luminosity since we measure directly the apparent luminosity, the inverse-square law allows us to estimate the distance to the object concerned. For the present discussion, it is important to understand that, at optical wavelengths, estimates of maximum rotation speeds are generally extrapolations from rotation curve measurements. 

The process of estimating the global redshift component and estimating the dynamical center is termed the process of folding the rotation curve. Because of the very noisy nature of the data, this process is very far from trivial, especially if one is interested in accurate dynamical studies of spiral galaxies. 

Persic, M., Salucci, P, Stel, F 1996. The universal rotation curve of spiral galaxies - I. The dark matter connection, MNRAS281, 27 Erratum ibid. 283, 1102(1996)... 

These considerations suggest that dynamical studies of bulge-dominated spirals can be wrong not only in their assessment of the visible M/L ratios but also in their inferences about dark halos. NIR imaging effectively probes the mass distribution due to lower extinction and to the more direct link to the stellar mass. When coupled with accurate rotation curves, NIR brightness profiles should provide the best means to determine the mass distribution in disk galaxies. 

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