SIMBAD references

A galaxy's stellar mass-to-light ratio (M_*/L) is a useful tool for converting luminosity to stellar mass (M_*). However, the practical utility of M_*/L inferred from stellar population synthesis (SPS) models is limited by mismatches between the real and assumed models for star-formation history (SFH) and dust geometry, both of which vary within galaxies. Here, we measure spatial variations in M_*/L and their dependence on color, SFH, and dust across the disk of M31, using a map of M_*^CMD derived from color-magnitude diagrams of resolved stars in the Panchromatic Hubble Andromeda Treasury survey. First, we find comparable scatter in M_*/L for the optical and mid-IR, contrary to the common idea that M_*/L is less variable in the IR. Second, we confirm that M_*/L is correlated with color for both the optical and mid-IR and report color versus M_*/L relations (CMLRs) in M31 for filters used in the Sloan Digital Sky Survey and Widefield Infrared Survey Explorer. Third, we show that the CMLR residuals correlate with recent SFH, such that quiescent regions are offset to higher M_*/L than star-forming regions at a fixed color. The mid-IR CMLR, however, is not linear due to the high scatter of M_*/L in star-forming regions. Finally, we find a flatter optical CMLR than any SPS-based CMLRs in the literature. We show that this is an effect of dust geometry, which is typically neglected but should be accounted for when using optical data to map M_*.