The sizes of galaxy halos in galaxy cluster Abell 1689

The multiple images observed in the galaxy cluster Abell 1689 provide strong constraints not only on the mass distribution of the cluster, but also on the ensemble properties of the cluster galaxies. Using parametric strong-lensing models for the cluster, and by assuming well-motivated scaling laws between the truncation radius s and the velocity dispersion sigma of a cluster galaxy, we are able to derive the sizes of the dark matter halos of cluster galaxies. For the scaling law expected for galaxies in the cluster environment (s proportional to sigma), we obtain s = 64(-14)(+15) (sigma/220 km s(-1)) kpc. For the scaling law used for galaxies in the field with s proportional to sigma(2), we find s = 66(-16)(+18) (sigma/220 km s(-1))(2) kpc. Compared to halos of field galaxies, the cluster galaxy halos in Abell 1689 are strongly truncated.