The evolution of rest-frame K-band properties of early-type galaxies from z=1 to the present

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 similar to 1 with accurately measured dynamical masses. We find that M/L-K evolves as Delta 1n (M/L-K) = (-1.18 +/- 0.10)z, which is slower than in the B band [Delta 1n (M/L-B) = (-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 x 10(11) M-circle dot evolve as Delta 1n (M/L-K) = (-1.01 +/- 0.16)z; less massive galaxies evolve as Delta 1n (M/L-K) = (-1.27 +/- 0.11)z. As expected from stellar population models, the evolution in M/L-K is slower than the evolution in M/L-B. 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.