A systematic search for very massive galaxies at z > 4

Motivated by the claimed discovery of a very massive galaxy (HUDF-JD2; M~5x10¹1 Msun) at extreme redshift (z = 6. 5) within the Hubble Ultra Deep Field (HUDF) (Mobasher et al. 2005), we have completed a systematic search for comparably massive galaxies with z > 4 among the 2688 galaxies in our K 4 candidates, performing aperture photometry on all images, and including marginal detections and formal non-detections in the fitting process. This led to the rejection of a further 13 galaxies to lower redshift. Moreover, subjecting HUDF-JD2 to the same analysis, we find that it lies at z ~ 2. 2, rather than the extreme redshift favoured by Mobasher et al. (2005). The 6 remaining candidates appear to be credible examples of galaxies in the redshift range z = 4 - 6, with plausible stellar ages. However, refitting with allowance for extreme values of extinction we find that, even for these objects, statistically acceptable solutions can be found at z 4 candidates are detected at 24 microns. We conclude that there is no convincing evidence for any galaxy with M > 3 x 10¹1 Msun, and z > 4 within the GOODS-South field (abridged).