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

We present stellar population models to calculate the mass-to-light ratio (ϒ(*)) based on galaxies' colors ranging from GALEX far-UV to Spitzer IRAC1 at 3.6 mu m. We present a new composite bulge+disk ϒ(*) 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 ϒ(*); however, a reasonable bulge+disk model plus total color only introduces 5% more uncertainty. Full bulge+disk ϒ(*) prescriptions applied to the baryonic Tully-Fisher relation improve the linearity of the correlation, increase the slope, and reduce the total scatter by 4%.