GALAXY GROUPS IN THE 2MASS REDSHIFT SURVEY

A galaxy group catalog is constructed from the 2MASS Redshift Survey (2MRS) with the use of a halo-based group finder. The halo mass associated with a group is estimated using a "GAP" method based on the luminosity of the central galaxy and its gap with other member galaxies. Tests using mock samples show. that this method is reliable, particularly for poor systems containing only a few members. On average, 80% of all the groups have completeness >0.8, and about 65% of the groups have zero contamination. Halo masses are estimated with a typical uncertainty of. similar to 0.35 dex. The application of the group finder to the 2MRS gives 29,904 groups from a total of 43,246 galaxies at z <= 0.08, with 5286 groups having two or more members. Some basic properties of this group catalog is presented, and comparisons are made with other group. catalogs in overlap regions. With a depth to z similar to 0.08 and uniformly covering about 91% of the whole sky, this group catalog provides a useful database to study galaxies in the local cosmic web, and to reconstruct the mass distribution in the local universe.