SDSS DR7 superclusters

Morphology

¹ Tartu Observatory, 61602 Tõravere, Estonia
e-mail: maret@aai.ee
² Institute of Physics, Tartu University, Tähe 4, 51010 Tartu, Estonia
³ Observatori Astronòmic, Universitat de València, Apartat de Correus 22085, 46071 València, Spain
⁴ Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, Finland

Received: 24 January 2011
Accepted: 2 May 2011

Abstract

Aims. We study the morphology of a set of superclusters drawn from the SDSS DR7.

Methods. We calculate the luminosity density field to determine superclusters from a flux-limited sample of galaxies from SDSS DR7 and select superclusters with 300 and more galaxies for our study. We characterise the morphology of superclusters using the fourth Minkowski functional V₃, the morphological signature (the curve in the shapefinder’s K₁-K₂ plane) and the shape parameter (the ratio of the shapefinders K₁/K₂). We investigate the supercluster sample using multidimensional normal mixture modelling. We use Abell clusters to identify our superclusters with known superclusters and to study the large-scale distribution of superclusters.

Results. The superclusters in our sample form three chains of superclusters; one of them is the Sloan Great Wall. Most superclusters have filament-like overall shapes. Superclusters can be divided into two sets; more elongated superclusters are more luminous, richer, have larger diameters and a more complex fine structure than less elongated superclusters. The fine structure of superclusters can be divided into four main morphological types: spiders, multispiders, filaments, and multibranching filaments. We present the 2D and 3D distribution of galaxies and rich groups, the fourth Minkowski functional, and the morphological signature for all superclusters.

Conclusions. Widely different morphologies of superclusters show that their evolution has been dissimilar. A study of a larger sample of superclusters from observations and simulations is needed to understand the morphological variety of superclusters and the possible connection between the morphology of superclusters and their large-scale environment.