[1012.1989] SDSS DR7 superclusters. The catalogues

Authors:  Lauri Juhan Liivamägi, Elmo Tempel, Enn Saar
Abstract:  We have constructed a supercluster catalogue for the galaxies from the SDSS survey main and Luminous Red Galaxy (LRG) samples. 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. To delineate superclusters, we calculate luminosity density fields using the B3-spline kernel of the radius of 8 Mpc/h and define regions with densities over a selected threshold as superclusters. We create two types of catalogues, one with an adaptive local threshold and a set of catalogues with different global thresholds. We present supercluster catalogues for both the SDSS main and LRG samples. We describe their properties and compare them with the supercluster catalogues for the Millennium simulation. We find that the superclusters are well-defined systems, and the properties of the superclusters of the main and LRG samples are similar. The Millennium galaxy catalogue provides similar superclusters to those observed.
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Syksy Rasanen
Posts: 119
Joined: March 02 2005
Affiliation: University of Helsinki

[1012.1989] SDSS DR7 superclusters. The catalogues

Post by Syksy Rasanen » December 16 2010

There a few claims of discrepancy between the observed distribution of structures on large scales and expectations from the [tex]\Lambda[/tex]CDM model. Issues include observed voids being too empty, filaments being too large and luminous ( http://cosmocoffee.info/viewtopic.php?t=1678&highlight= ), clusters being too large too early ( http://cosmocoffee.info/viewtopic.php?t=1660&highlight= ) and the fractal dimension being different on all scales between 1 and 100 Mpc ( http://cosmocoffee.info/viewtopic.php?t=1543&highlight= ).

One topic is the number of luminous superclusters. It has been argued in astro-ph/0603764, astro-ph/0604539 and astro-ph/0605393 that the number of luminous superclusters in observations higher than in [tex]\Lambda[/tex]CDM simulations by a factor of a few.

This paper is a new comparison of superclusters in the SDSS main survey and LRG sample with the Millennium simulation. I found it difficult to follow the various steps of the analysis to have an intuitive picture of what the superclusters here correspond to. One difference from previous analyses is that the definition of superclusters involves the overdensity relative to the local density, not the cosmic mean density.

The authors conclude that the properties of the observed and simulated catalogues are similar (if anything, the simulation has slightly more superclusters), in contrast to previous work. Since the definition of superclusters is different, the papers may not be in disagreement. However, the authors find an overall density variation, and variation of supercöluster properties on 200 [tex]h^{-1}[/tex] Mpc scales in SDSS. They say they will return to this in their next paper. I wonder if this is related to what Sylos Labini et al have discussed for some time now, see e.g. 0910.3833 and 1011.4855.

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