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| Paper: |
Evolution and Formation of Early-Types in Clusters: Old Disk Galaxies |
| Volume: |
230, Galaxy Disks and Disk Galaxies |
| Page: |
581 |
| Authors: |
Franx, M.; van Dokkum, P. G. |
| Abstract: |
Old disk galaxies can be found in large numbers in rich clusters, in the form of S0 galaxies. The S0 galaxies and ellipticals form a homogeneous population in rich clusters, and they have evolved slowly between z=0.8 and z=0. This has generally been interpreted as evidence that they are very old. On the other hand, recent evidence suggests that many early-type galaxies in rich clusters have been transformed from spirals since z ≈ 0.5-0.8. We explore models for the evolution of early-type galaxies which incorporate the morphological evolution explicitly, and we show that the homogeneity, slow evolution, and morphological transformations can be brought into agreement. Due to the morphological evolution the sample of early-type galaxies at high redshift is only a subsample of the sample of early-type galaxies at low redshift. This can produce a bias, as the early-types at high redshift are the oldest early-types at low redshift. This `progenitor bias' results into an overestimate of the mean formation redshift if simple models without morphological transformations are used. The correction to the mean formation redshift can be constrained from the scatter in the color-magnitude relation, and the scatter in the M/L ratios. We find that the derived formation redshifts lie between 3 and 6.5 in an open universe, corresponding to the maximal and minimal correction. |
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