Merging groups and clusters of galaxies from the SDSS data. The catalogue of groups and potentially merging systems

TL;DR

This paper presents a new catalogue of galaxy groups and clusters from SDSS data, identifying merging systems and analyzing their properties to aid cosmological studies.

Contribution

It introduces a modified friends-of-friends method for flux-limited surveys and identifies merging systems and substructures within galaxy groups.

Findings

Catalogue of 88,662 galaxy groups with at least two members

Identification of 4,983 potential merging systems

Observation that mass-to-light ratio increases with group richness

Abstract

Galaxy groups and clusters are the main tools used to test cosmological models and to study the environmental effect of galaxy formation. This work provides a catalogue of galaxy groups and clusters, as well as potentially merging systems based on the SDSS main galaxy survey. We identified galaxy groups and clusters using the modified friends-of-friends (FoF) group finder designed specifically for flux-limited galaxy surveys. The FoF group membership is refined by multimodality analysis to find subgroups and by using the group virial radius and escape velocity to expose unbound galaxies. We look for merging systems by comparing distances between group centres with group radii. The analysis results in a catalogue of 88662 galaxy groups with at least two members. Among them are 6873 systems with at least six members which we consider to be more reliable groups. We find 498 group mergers with up to six groups. We performed a brief comparison with some known clusters in the nearby Universe, including the Coma cluster and Abell 1750. The Coma cluster in our catalogue is a merging system with six distinguishable subcomponents. In the case of Abell 1750 we find a clear sign of filamentary infall toward this cluster. Our analysis of mass-to-light ratio (M/L) of galaxy groups reveals that M/L slightly increases with group richness.