Stellar Mass-to-light Ratios: Composite Bulge+Disk Models and the Baryonic Tully-Fisher Relation

We present stellar population models to calculate the mass-to-light ratio ($\Upsilon_*$) based on galaxy's colors ranging from $GALEX$ FUV to Spitzer IRAC1 at 3.6$\mu$m. We present a new composite bulge+disk $\Upsilon_*$ model that considers the varying contribution from bulges and disks based on their optical and near-IR colors. Using these colors, we build plausible star formation histories and chemical enrichment scenarios based on the star formation rate-stellar mass and mass-metallicity correlations for star-forming galaxies. The most accurate prescription is to use the actual colors for the bulge and disk components to constrain $\Upsilon_*$; however, a reasonable bulge+disk model plus total color only introduces 5% more uncertainty. Full bulge+disk $\Upsilon_*$ prescriptions applied to the baryonic TF relation improves the linearity of the correlation, increases the slope and reduces the total scatter by 4%.