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Description
We measure the relation between galaxy luminosity and disk circular velocity (the Tully-Fisher [TF] relation), in the g, r, i, and z bands, for a broadly selected sample of galaxies from the Sloan Digital Sky Survey, with the goal of providing well-defined observational constraints for theoretical models of galaxy formation. The input sample of 234 galaxies has a roughly flat distribution of absolute magnitudes in the range -18.5>M_r_>-22, and our only morphological selection is an isophotal axis ratio cut b/a<=0.6 to allow accurate inclination corrections. Long-slit spectroscopy from the Calar Alto and MDM observatories yields usable Halpha rotation curves for 162 galaxies (69%), with a representative color and morphology distribution. We define circular velocities V_80_ by evaluating the rotation curve at the radius containing 80% of the i-band light.
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