Stellar M/L ratios and spiral galaxy dynamics

We present a simple technique to estimate mass-to-light (M/L) ratios of stellar populations in local universe galaxies based on two broadband photometry measurements, i.e. a color-M/L relation. The method is significantly better than using a fixed M/L, even in the near-IR. The main uncertainty sterns from the assumed stellar IMF, which results in a zero-point uncertainty of the color-M/L relation. We constrain the zero-point using maximum disk rotation curve limits. We apply the color-M/L relation to the Tully-Fisher relation and show there is a universal stellar mass Tully-Fisher relation, independent of observed passband. We also apply the relation to galaxy rotation curves, but have to conclude that the current data is insufficient to constrain dark matter profile shapes across the full range of galaxy luminosities.