Recent work has suggested that mid-IR wavelengths are optimal for estimating the mass-to-light ratios of stellar populations and hence the stellar masses of galaxies .
We compare stellar masses deduced from spectral energy distribution ( SED ) models , fitted to multi-wavelength optical-NIR photometry , to luminosities derived from WISE photometry in the W 1 and W 2 bands at 3.6 and 4.5 \mu m for non-star forming galaxies .
The SED derived masses for a carefully selected sample of low redshift ( z \leq 0.15 ) passive galaxies agree with the prediction from stellar population synthesis models that M _ { * } / L _ { W 1 } \simeq 0.6 for all such galaxies , independent of other stellar population parameters .
The small scatter between masses predicted from the optical SED and from the WISE measurements implies that random errors ( as opposed to systematic ones such as the use of different IMFs ) are smaller than previous , deliberately conservative , estimates for the SED fits .
This test is subtly different from simultaneously fitting at a wide range of optical and mid-IR wavelengths , which may just generate a compromise fit : we are directly checking that the best fit model to the optical data generates an SED whose M _ { * } / L _ { W 1 } is also consistent with separate mid-IR data .
We confirm that for passive low redshift galaxies a fixed M _ { * } / L _ { W 1 } = 0.65 can generate masses at least as accurate as those obtained from more complex methods .
Going beyond the mean value , in agreement with expectations from the models , we see a modest change in M _ { * } / L _ { W 1 } with SED fitted stellar population age but an insignificant one with metallicity .