Sizes, colour gradients and resolved stellar mass distributions for the massive cluster galaxies in XMMUJ2235-2557 at z = 1.39

• Published in: Monthly notices of the Royal Astronomical Society 2016-05, Vol.458 (3), p.3181-3209
• Main Authors: 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, Stott, John P.
• Format: Article
• Language: English
• Subjects: Age; Astrophysics; Color; Colour; Correlation; Correlation analysis; Evolution; Galactic clusters; Galaxies; Optics; Red shift; Spectrum analysis; Star & galaxy formation; Stellar mass; Telescopes
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw502

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 Sérsic fits in five HST bands (i 775, z 850, Y 105, J 125, H 160), and find that the size decreases by ∼20 per cent going from i 775 to H 160 band, consistent with recent studies. We then generate spatially resolved stellar mass maps using an empirical relationship between $M_{{\ast }}/L_{H_{160}}$ and (z 850 − H 160) and use these to derive mass-weighted Sérsic fits: the mass-weighted sizes are ∼41 per cent smaller than their rest-frame r-band counterparts compared with an average of ∼12 per cent at z ∼ 0. We attribute this evolution to the evolution in the $M_{{\ast }}/L_{H_{160}}$ 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 (∇ z − H ) are mostly negative, with a median value of ∼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 ∇age = dlog (age)/dlog (a) ∼− 0.33, while the survival of weaker colour gradients in old, local galaxies implies that metallicity gradients are also required, with ∇ Z  = dlog (Z)/dlog (a) ∼− 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.