The Evolution of Rest-frame K-band Properties of Early-type Galaxies

We measure the evolution of the rest-frame K-band Fundamental Plane from z = 1 to the present by using IRAC imaging of a sample of early-type galaxies in the Chandra Deep Field-South at z ∼ 1 with accurately measured dynamical masses. We find that M/LK evolves as ∆ ln (M/LK) = (−1.18± 0.10)z, which is slower than in the B-band (∆ ln (M/LB) = (−1.46 ± 0.09)z). In the B-band the evolution has been demonstrated to be strongly mass dependent. In the K-band we find a weaker trend: galaxies more massive than M = 2 × 10M⊙ evolve as ∆ ln (M/LK) = (−1.01 ± 0.16)z; less massive galaxies evolve as ∆ ln (M/LK) = (−1.27± 0.11)z. As expected from stellar population models the evolution in M/LK is slower than the evolution in M/LB. However, when we make a quantitative comparison, we find that the single burst Bruzual-Charlot models do not fit the results well, unless large dust opacities are allowed at z = 1. Models with a flat IMF fit better, Maraston models with a different treatment of AGB stars fit best. These results show that the interpretation of rest-frame near-IR photometry is severely hampered by model uncertainties and therefore that the determination of galaxy masses from rest-frame near-IR photometry may be harder than was thought before. Subject headings: cosmology: observations—galaxies: evolution—galaxies: formation