Color--Mass-to-Light Ratio Relations for Disk Galaxies

TL;DR

This study tests and revises color--mass-to-light ratio relations for disk galaxies using multi-wavelength data, highlighting discrepancies in models and providing more consistent relations, especially in the near-infrared.

Contribution

The paper introduces revised color--mass-to-light ratio relations that improve the consistency of stellar mass estimates across different wavelengths for disk galaxies.

Findings

Many models fail to produce consistent stellar masses across bands.

The $B-V$ color is a reliable indicator of mass-to-light ratio.

Near-infrared mass-to-light ratios are weakly dependent on color.

Abstract

We combine Spitzer $3.6\mu$ observations of a sample of disk galaxies spanning over 10 magnitudes in luminosity with optical luminosities and colors to test population synthesis prescriptions for computing stellar mass. Many commonly employed models fail to provide self-consistent results: the stellar mass estimated from the luminosity in one band can differ grossly from that of another band for the same galaxy. Independent models agree closely in the optical ($V$-band), but diverge at longer wavelengths. This effect is particularly pronounced in recent models with substantial contributions from TP-AGB stars. We provide revised color--mass-to-light ratio relations that yield self-consistent stellar masses when applied to real galaxies. The $B-V$ color is a good indicator of the mass-to-light ratio. Some additional information is provided by $V-I$, but neither it nor $J-K_s$ are particularly useful for constraining the mass-to-light ratio on their own. In the near-infrared, the mass-to-light ratio depends weakly on color, with typical values of $0.6\; \mathrm{M}_{\odot}/\mathrm{L}_{\odot}$ in the $K_s$-band and $0.47\; \mathrm{M}_{\odot}/\mathrm{L}_{\odot}$ at $3.6\mu$.