SDSS DR7 superclusters. The catalogues

TL;DR

This paper constructs and analyzes supercluster catalogues from SDSS data, comparing observed and simulated superclusters, and assessing their properties and uncertainties using density fields and thresholds.

Contribution

It introduces new supercluster catalogues using adaptive and global density thresholds, and compares observed superclusters with Millennium simulation data.

Findings

Superclusters are well-defined systems with similar properties in SDSS and Millennium data.

Adaptive thresholds produce supercluster samples independent of distance from observer.

Uncertainty estimates for density fields are derived using bootstrap methods.

Abstract

We have constructed a set of supercluster catalogues for the galaxies from the SDSS survey main and luminous red galaxy (LRG) flux-limited samples. To delineate superclusters, we calculated luminosity density fields using the B3-spline kernel of the radius of 8 Mpc/h for the main sample and 16 Mpc/h for the LRG sample and define regions with densities over a selected threshold as superclusters, while utilising almost the whole volume of both samples. We created two types of catalogues, one with an adaptive local threshold and a set of catalogues with different global thresholds. We describe the supercluster catalogues and their general properties. Using smoothed bootstrap, we find uncertainty estimates for the density field and use these to attribute confidence levels to the catalogue objects. We have also created a test catalogue for the galaxies from the Millennium simulation to compare the simulated and observed superclusters and to clarify the methods we use. We find that the superclusters are well-defined systems, and the properties of the superclusters of the main and LRG samples are similar. We also show that with adaptive local thresholds we get a sample of superclusters, the properties of which do not depend on their distance from the observer. The Millennium galaxy catalogue superclusters are similar to those observed.