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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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