SDSS DR7 groups, clusters and filaments

Our "multiscale probability mapping" technique combines density estimation with a shape statistic to identify local peaks in the density field. This technique takes advantage of a user-defined range of scale sizes, which are used in constructing a coarse-grained map of the underlying fine-grained galaxy distribution, from which overdense structures are then identified.

In this study we have compiled a catalogue of groups and clusters at 0.025<z<0.24 based on the Sloan Digital Sky Survey (SDSS), Data Release 7, quantifying their significance and comparing with other catalogues. Most measured velocity dispersions for these structures lie between 50 and 400km/s. A clear trend of increasing velocity dispersion with radius from 0.2 to 1Mpc/h is detected, confirming the lack of a sharp division between groups and clusters.