paper

Being WISE II: Reducing the Influence of Star Formation History on the Mass-to-Light Ratio of Quiescent Galaxies

arXiv:1608.07584 · doi:10.3847/0004-637X/832/2/198

Abstract

Stellar population synthesis models can now reproduce the photometry of old stellar systems (age 2 Gyr) in the near-infrared (NIR) bands at 3.4 and 4.6m (WISE W1 W2 or IRAC 1 2). In this paper we derive stellar mass-to-light ratios for these and optical bands, and confirm that the NIR M/L shows dramatically reduced sensitivity to both age and metallicity compared to optical bands, and further, that this behavior leads to significantly more robust stellar masses for quiescent galaxies with [Fe/H] > -0.5 regardless of star formation history (SFH). We then use realistic early-type galaxy SFHs and metallicity distributions from the EAGLE simulations of galaxy formation to investigate two methods to determine the appropriate M/L for a galaxy: 1) We show that the uncertainties introduced by an unknown SFH can be largely removed using a spectroscopically inferred luminosity-weighted age and metallicity for the population to select the appropriate single stellar population (SSP) equivalent M/L. Using this method, the maximum systematic error due to SFH on the M/L of an early-type galaxy is 4 at 3.4 m and typical uncertainties due to errors in the age and metallicity create scatter of 13. The equivalent values for optical bands are more than 2-3 times greater, even before considering uncertainties associated with internal dust extinction. 2) We demonstrate that if the EAGLE SFHs and metallicities accurately reproduce the true properties of early-type galaxies, the use of an iterative approach to select a mass dependent M/L can provide even more accurate stellar masses for early-type galaxies, with typical uncertainties 9.

15 pages, 11 figures. Accepted for publication in ApJ

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