Toward Understanding Rich Superclusters

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Abstract
We present a morphological study of the two richest superclusters from the 2dFGRS (SCl 126, the Sloan Great Wall, and SCl 9, the Sculptor supercluster). We use Minkowski functionals, shapefinders, and galaxy group information to study the substructure of these superclusters as formed by different populations of galaxies. We compare the properties of grouped and isolated galaxies in the core region and in the outskirts of superclusters. The fourth Minkowski functional V3 and the morphological signature K1-K2 show a crossover from low-density morphology (outskirts of supercluster) to high-density morphology (core of supercluster) at mass fraction mf ≈ 0.7. The galaxy content and the morphology of the galaxy populations in supercluster cores and outskirts are different. The core regions contain a larger fraction of early-type, red galaxies and richer groups than the outskirts of superclusters. In the core and outskirt regions the fine structure of the two prominent superclusters as delineated by galaxies from different populations also differs. The values of the fourth Minkowski functional V3 show that in the supercluster SCl 126 the population of early-type, red galaxies is more clumpy than that of late-type, blue galaxies, especially in the outskirts of the supercluster. On the contrary, in the supercluster SCl 9, the clumpiness of the spatial distribution of galaxies of different type and color is quite similar in the outskirts of the supercluster, while in the core region the clumpiness of the late-type, blue galaxy population is larger than that of the early-type, red galaxy population. Our results suggest that both local (group/cluster) and global (supercluster) environments are important in forming galaxy morphologies and colors (and determining the star formation activity). The differences between the superclusters indicate that these superclusters have different evolutional histories.
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