PPT Slide
So: we hypothesise that these red things are elliptical galaxies that formed the bulk of their stars around half a Gyr before we observe them (zɰ). Control surveys such as the ESO imaging survey are not finding objects with colours like these: once again our cluster region is very significantly overdense. They all seem to lie within a volume of around one cubic proper Mpc.
We may have been lucky to catch them at an age of only half a Gyr: during the next Gyr or so passive evolution will decrease their brightness by two or more magnitudes, making them very hard to see (and also diminishing the contrast of the H-band peak).
These would be the most distant elliptical galaxies yet seen.