Galaxy formation and evolution

Abstract:

{abridged} We present imaging and spectroscopy of Abell 1689 (z=0.183) from GEMINI/GMOS-N and HST/ACS. We measure integrated photometry from the GMOS g' and r' 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 relation (KR), Faber-Jackson relation (FJR) and colour-magnitude relation (CMR) 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 CMR in Abell 1689 to be 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 KR & FJR 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 KR & FJR 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+inf-0.9). Thus the changes in the KR, FJR & CMR 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.

Abstract:

We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the massive cluster Abell 1689 at z = 0.183. Conducting an analysis similar to that of ATLAS3D, we extend the baseline of the kinematic morphology-density relation by an order of magnitude in projected density and show that it is possible to use existing instruments to identify slow and fast rotators beyond the local Universe. We find 4.5 +- 1.0 slow rotators with a distribution in magnitude similar to those in the Virgo cluster. The overall slow rotator fraction of our Abell 1689 sample is 0.15 +- 0.03, the same as in Virgo using our selection criteria. This suggests that the fraction of slow rotators in a cluster is not strongly dependent on its density. However, within Abell 1689, we find that the fraction of slow rotators increases towards the centre, as was also found in the Virgo cluster.