Panoramic Views of Cluster-Scale Assemblies Explored by Subaru   Wide-Field Imaging
  We have started PISCES project; a panoramic imaging and spectroscopic survey of distant clusters on Subaru. It exploits the unique wide-field imaging capability of Suprime-Cam, which provides a 34'x27' field of view corresponding to a physical area of 16x13Mpc^2 at z~1. We plan to target 15 clusters in total at 0.4<z<1.3. In this paper, we report on our first results concerning the inner structures and large-scale structures of two distant clusters at z=0.55 and 0.83 together with the earlier results on a z=0.41 cluster. The photometric redshift technique has been applied to multi-color data in order to efficiently remove most of the foreground/background galaxies so as to isolate the cluster member candidates. We have found large-scale filamentary structures around the clusters, extending out to >5Mpc from the cores, as well as complex inner structures. The galaxy distributions in the inner regions of the clusters look similar to the X-ray intensity maps, suggesting that most of the optical structures trace physically bound systems. We also compared the structures of the three clusters with those of model clusters in a numerical simulation (N-body + semi-analytic model) by parameterising the shapes of the iso-density contours of galaxies, and found a broad agreement. Our results provide good evidence that cluster-scale assembly takes place along filaments during hierarchical clustering, while the structures found here need to be confirmed spectroscopically in the near future. 
Tadayuki Kodama (National Astronomical Observatory of Japan) and the   PISCES team