Early-type galaxies at z = 1.3. I. The Lynx supercluster: cluster and
  groups at z=1.3. Morphology and color-magnitude relation
  We confirm the detection of 3 groups in the Lynx supercluster, at z~1.3, and
give their redshifts and masses. We study the properties of the group galaxies
as compared to the central clusters, RXJ0849+4452 and RXJ0848+4453, selecting
89 galaxies in the clusters and 74 galaxies in the groups. We morphologically
classify galaxies by visual inspection, noting that our early-type galaxy (ETG)
sample would have been contaminated at the 30% -40% level by simple automated
classification methods (e.g. based on Sersic index). In luminosity selected
samples, both clusters and groups show high fractions of Sa galaxies. The ETG
fractions never rise above ~50% in the clusters, which is low compared to the
fractions observed in clusters at z~1. However, ETG plus Sa fractions are
similar to those observed for ETGs in clusters at z~1. Bulge-dominated galaxies
visually classified as Sas might also be ETGs with tidal features or merger
remnants. They are mainly red and passive, and span a large range in
luminosity. Their star formation seems to have been quenched before
experiencing a morphological transformation. Because their fraction is smaller
at lower redshifts, they might be the spiral population that evolves into ETGs.
For mass-selected samples, the ETG fraction show no significant evolution with
respect to local clusters, suggesting that morphological transformations occur
at lower masses and densities. The ETG mass-size relation shows evolution
towards smaller sizes at higher redshift in both clusters and groups, while the
late-type mass-size relation matches that observed locally. The group ETG red
sequence shows lower zero points and larger scatters than in clusters, both
expected to be an indication of a younger galaxy population. The estimated age
difference is small when compared to the difference in age at different galaxy
masses.
