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.

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