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Beifiori, Alessandra, Mendel, J. Trevor, Chan, Jeffrey C. C., Saglia, Roberto P., Bender, Ralf, Cappellari, Michele, Davies, Roger L., Galametz, Audrey, Houghton, Ryan C. W., Prichard, Laura J., Smith, Russell, Stott, John P., Wilman, David J., Lewis, Ian J., Sharples, Ray and Wegner, Michael (2017): The KMOS Cluster Survey (KCS). I. The Fundamental Plane and the Formation Ages of Cluster Galaxies at Redshift 1.4 < Z < 1.6. In: Astrophysical Journal, Vol. 846, No. 2, 120

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We present the analysis of the fundamental plane (FP) for a sample of 19 massive red-sequence galaxies (M-star > 4 x 10(10) M-circle dot) 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(star)/M-circle dot > 11) in our sample, we translate the FP zero-point evolution into a mass-to-light-ratio M/ L evolution, finding Delta logM/L-B =(-0.46 +/- 0.10) z, Delta logM/L-B =(-0.52 +/- 0.07) z, to Delta logM/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 similar to 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(star)/M-circle dot > 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.

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