The stellar Mass–to–Light ratio in disc galaxies

Abstract

The mass and distribution of baryons in galaxies is closely related to the inferred structure of the dark halo. A robust estimate of the baryon content requires knowledge of the typical mass–to–light (M/L) ratio of the stellar component. Various arguments favour a low M*/LI < 1 for late–type spirals. We show that “bottom-light” Initial Mass Functions (IMFs) favoured by recent literature do yield so low M/L ratios, for Sbc/Sc discs. We also predict the stellar M/L ratio, and hence the zero–point of the Tully–Fisher relation, to vary significantly with Hubble disc type. Finally, we provide colour–M/L relations to derive the stellar M/L ratio from the observed photometry, for different IMFs.