Comparing Dynamical and Photometric Mass Estimates of Low- and High-Redshift Galaxies: Random and Systematic Uncertainties

Abstract

We determine the importance of redshift-dependent systematic effects in the determination of stellar masses from broadband spectral energy distributions (SEDs), using high-quality kinematic and photometric data of early-type galaxies at z~1 and z~0. We find that photometric masses of z~1 galaxies can be systematically different, by up to a factor of 2, from photometric masses of z~0 galaxies with the same dynamical mass. The magnitude of this bias depends on the choice of stellar population synthesis model and the rest-frame wavelength range used in the fits. The best result, i.e., without significant bias, is obtained when rest-frame optical SEDs are fitted with models from Bruzual & Charlot. When the SEDs are extended to the rest-frame near-IR, a bias is introduced: photometric masses of the z~1 galaxies increase by a factor of 2 relative to the photometric masses of the z~0 galaxies. When we use the Maraston models, the photometric masses of the z~1 galaxies are low relative to the photometric masses of the z~0 galaxies by a factor of ~1.8. This offset occurs both for fits based on rest-frame optical SEDs and fits based on rest-frame optical+near-IR SEDs. The results indicate that model uncertainties produce uncertainties as high as a factor of 2.5 in mass estimates from rest-frame near-IR photometry, independent of uncertainties due to unknown star formation histories.

Based on observations collected at the European Southern Observatory, Chile (168.A-0485, 169.A-0458) on observations with the Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555 and in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.