We determine the importance of redshift-dependent systematic effects in the determination of stellar masses from broad band 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 (2003). 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 (2005) 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.
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