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Tully-Fisher

Tully-Fisher. Measure rotation velocity V of spiral galaxy Assuming circular orbits and spherical symmetry, Assuming constant surface brightness, L  R 2 , and constant mass-to-light ratio, L  M , we get R  V 2 and L  V 4 , i.e. M = −10 log V + constant

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Tully-Fisher

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  1. Tully-Fisher • Measure rotation velocity V of spiral galaxy • Assuming circular orbits and spherical symmetry, • Assuming constant surface brightness, L R2, and constant mass-to-light ratio, L  M, we get R  V2 and L  V4, i.e. M = −10 log V + constant • in fact, fit M = −a log V + b • a≈ −10 for infra-red, but not for visible light (star formation?) • good correlation • cosmologicallyinteresting • dark halo → massbaryons → light Giovanelli et al., AJ113 (1997) 53 PHY306

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