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Chan, Jeffrey C. C.; Beifiori, Alessandra; Mendel, J. Trevor; Saglia, Roberto P.; Bender, Ralf; Fossati, Matteo; Galametz, Audrey; Wegner, Michael; Wilman, David J.; Cappellari, Michele; Davies, Roger L.; Houghton, Ryan C. W.; Prichard, Laura J.; Lewis, Ian J.; Sharples, Ray and Stott, John P. (2016): Sizes, colour gradients and resolved stellar mass distributions for the massive cluster galaxies in XMMUJ2235-2557 at z=1.39. In: Monthly Notices of the Royal Astronomical Society, Vol. 458, No. 3: pp. 3181-3209

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We analyse the sizes, colour gradients and resolved stellar mass distributions for 36 massive and passive galaxies in the cluster XMMUJ2235-2557 at z = 1.39 using optical and near-infrared Hubble Space Telescope (HST) imaging. We derive light-weighted Sersic fits in five HST bands (i(775), z(850), Y-105, J(125), H-160), and find that the size decreases by similar to 20 per cent going from i(775) to H-160 band, consistent with recent studies. We then generate spatially resolved stellarmassmaps using an empirical relationship between M-*/L-H160 and (z(850) - H-160) and use these to derive mass-weighted Sersic fits: the mass-weighted sizes are similar to 41 per cent smaller than their rest-frame r-band counterparts compared with an average of similar to 12 per cent at z similar to 0. We attribute this evolution to the evolution in the M-*/L-H160 and colour gradient. Indeed, as expected, the ratio of mass-weighted to light-weighted size is correlated with the M-*/L gradient, but is also mildly correlated with the mass surface density and mass-weighted size. The colour gradients (del(z -H)) are mostly negative, with a median value of similar to 0.45 mag dex(-1), twice the local value. The evolution is caused by an evolution in age gradients along the semimajor axis (a), with del(age) = dlog (age)/dlog (a) similar to-0.33, while the survival of weaker colour gradients in old, local galaxies implies that metallicity gradients are also required, with del(Z) = dlog (Z)/dlog (a) similar to-0.2. This is consistent with recent observational evidence for the inside-out growth of passive galaxies at high redshift, and favours a gradual mass growth mechanism, such as minor mergers.

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