THE FUNDAMENTAL PLANE OF MASSIVE QUIESCENT GALAXIES OUT TO Z ∼ 2

The Fundamental Plane (FP) of early-type galaxies, relating the effective radius, velocity dispersion, and surface brightness, has long been recognized as a unique tool for analyzing galaxy structure and evolution. With the discovery of distant quiescent galaxies and the introduction of high sensitivity near-infrared spectrographs, it is now possible to explore the FP out to z similar to 2. In this Letter we study the evolution of the FP out to z similar to 2 using kinematic measurements of massive quiescent galaxies (M-* > 10(11)M(circle dot)). We find preliminary evidence for the existence of an FP out to z similar to 2. The scatter of the FP, however, increases from z similar to 0 to z similar to 2, even when taking into account the larger measurement uncertainties at higher redshifts. We find a strong evolution of the zero point from z similar to 2 to z similar to 0 : Delta log(10) M/L-g alpha (-0.49 +/- 0.03)z. In order to assess whether our spectroscopic sample is representative of the early-type galaxy population at all redshifts, we compare their rest-frame g - z colors with those from a larger mass complete sample of quiescent galaxies. At z > 1 we find that the spectroscopic sample is bluer. We use the color offsets to estimate a mass-to-light ratio (M/L) correction. The implied FP zero point evolution after correction is significantly smaller: Delta log(10) M/L-g alpha (-0.39 +/- 0.02)z. This is consistent with an apparent formation redshift of z(form) = 6.62(-1.44)(+3.19) for the underlying population, ignoring the effects of progenitor bias. A more complete spectroscopic sample is required at z similar to 2 to properly measure the M/L evolution from the FP evolution.