We present imaging and spectroscopy of Abell 1689 ( z=0.183 ) from the GMOS multi-object spectrograph on the Gemini-North telescope and the Advanced Camera for Surveys ( ACS ) on the Hubble Space Telescope ( HST ) .
We measure integrated photometry from the GMOS g ^ { \prime } and r ^ { \prime } images ( for 531 galaxies ) and surface photometry from the HST F625W image ( for 43 galaxies ) as well as velocities and velocity dispersions from the GMOS spectra ( for 71 galaxies ) .
We construct the Kormendy , Faber–Jackson and colour-magnitude relations for early-type galaxies in Abell 1689 using this data and compare them to those of the Coma cluster .
We measure the intrinsic scatter of the colour–magnitude relation in Abell 1689 to be \sigma _ { \textrm { \tiny CMR } } = 0.054 \pm 0.004 mag which places degenerate constraints on the ratio of the assembly timescale to the time available ( \beta ) and the age of the population .
Making the assumption that galaxies in Abell 1689 will evolve into those of Coma over an interval of 2.26 Gyr breaks this degeneracy and limits \beta to be > 0.6 and the age of the red sequence to be > 5.5 Gyr ( formed at z > 0.55 ) .
Without corrections for size evolution but accounting for magnitude cuts and selection effects , the Kormendy and Faber–Jackson relations are inconsistent and disagree at the 2 \sigma level regarding the amount of luminosity evolution in the last 2.26 Gyr .
However , after correcting for size evolution the Kormendy and Faber–Jackson relations show similar changes in luminosity ( 0.22 \pm { 0.11 } mag ) that are consistent with the passive evolution of the stellar populations from a single burst of star formation 10.2 \pm { 3.3 } Gyr ago ( z = 1.8 \pm _ { 0.9 } ^ { \infty } ) .
Thus the changes in the Kormendy , Faber–Jackson and colour-magnitude relations of Abell 1689 relative to Coma all agree and suggest old galaxy populations with little or no synchronisation in the star formation histories .
Furthermore , the weak evidence for size evolution in the cluster environment in the last 2.26 Gyr places interesting constraints on the possible mechanisms at work , favouring harassment or secular processes over merger scenarios .