2017ApJ...846..120B

We present the analysis of the fundamental plane (FP) for a sample of 19 massive red-sequence galaxies (M_* 4×10¹⁰M_☉) in three known overdensities at 1.39 z 1.61 from the K-band Multi-object Spectrograph (KMOS) Cluster Survey, a guaranteed-time program with spectroscopy from the KMOS at the VLT and imaging from the Hubble Space Telescope. As expected, we find that the FP zero-point in B band evolves with redshift, from the value 0.443 of Coma to -0.10 ± 0.09, -0.19 ± 0.05, and -0.29 ± 0.12 for our clusters at z = 1.39, z = 1.46, and z = 1.61, respectively. For the most massive galaxies (logM_*/M_☉ 11) in our sample, we translate the FP zero-point evolution into a mass-to-light-ratio M/L evolution, finding ΔlogM/L_B=(-0.46±0.10)z, ΔlogM/L_B=(-0.52±0.07)z, to ΔlogM/L_B=(-0.55±0.10)z, respectively. We assess the potential contribution of the galaxy structural and stellar velocity dispersion evolution to the evolution of the FP zero-point and find it to be ∼6%-35% of the FP zero-point evolution. The rate of M/L evolution is consistent with galaxies evolving passively. Using single stellar population models, we find an average age of 2.33_–0.51^+0.86 Gyr for the logM_*/M_☉ 11 galaxies in our massive and virialized cluster at z = 1.39, 1.59_–0.62^+1.40 Gyr in a massive but not virialized cluster at z = 1.46, and 1.20_–0.47^+1.03 Gyr in a protocluster at z = 1.61. After accounting for the difference in the age of the universe between redshifts, the ages of the galaxies in the three overdensities are consistent within the errors, with possibly a weak suggestion that galaxies in the most evolved structure are older.