We provide flux-and volume-limited galaxy group and cluster catalogues based on the spectroscopic sample of the galaxies of SDSS data release 10. We used a modified friends-of-friends method with a variable linking length in the transverse and radial directions to identify as many realistic groups as possible. The flux-limited catalogue incorporates galaxies down to m r = 17.77 mag. It includes 588 193 galaxies and 82 458 groups. The volume-limited catalogues are complete for absolute magnitudes down to M r,lim = −18.0, −18.5, −19.0, −19.5, −20.0, −20.5, and −21.0; the completeness is achieved within different spatial volumes. Our analysis shows that flux-and volume-limited group samples are well compatible, especially for the larger groups/clusters. Dynamical mass estimates based on radial velocity dispersions and group extent in the sky were added to the extracted groups.

Context. Groups form the most abundant class of galaxy systems. They act as the principal drivers of galaxy evolution and can be used as tracers of the large-scale structure and the underlying cosmology. However, the detection of galaxy groups from galaxy redshift survey data is hampered by several observational limitations. Aims. We improve the widely used friends-of-friends (FoF) group finding algorithm with membership refinement procedures and apply the method to a combined dataset of galaxies in the local Universe. A major aim of the refinement is to detect subgroups within the FoF groups, enabling a more reliable suppression of the fingers-of-God effect. Methods. The FoF algorithm is often suspected of leaving subsystems of groups and clusters undetected. We used a galaxy sample built of the 2MRS, CF2, and 2M++ survey data comprising nearly 80 000 galaxies within the local volume of 430 Mpc radius to detect FoF groups. We conducted a multimodality check on the detected groups in search for subgroups. We furthermore refined group membership using the group virial radius and escape velocity to expose unbound galaxies. We used the virial theorem to estimate group masses. Results. The analysis results in a catalogue of 6282 galaxy groups in the 2MRS sample with two or more members, together with their mass estimates. About half of the initial FoF groups with ten or more members were split into smaller systems with the multimodality check. An interesting comparison to our detected groups is provided by another group catalogue that is based on similar data but a completely different methodology. Two thirds of the groups are identical or very similar. Differences mostly concern the smallest and largest of these other groups, the former sometimes missing and the latter being divided into subsystems in our catalogue.

Context. Galaxy groups and clusters are the main tools used to test cosmological models and to study the environmental effect of galaxy formation. Aims. This work provides a catalogue of galaxy groups and clusters, as well as potentially merging systems based on the SDSS main galaxy survey. Methods. 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. Results. The analysis results in a catalogue of 88 662 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.