The Multiplicity Function of groups of galaxies from CRoNaRio catalogues

The projected multiplicity function of galaxies gives (per square degree) the density of galaxy aggregates formed by N members. We use the CRoNaRio matched catalogues to derive the low N (N<15) multiplicity function from D-POSS data. The van Albada (1982) algorithm was implemented and used to identify candidate groups in the CRoNaRio catalogues. In absence of redshift surveys complete down to the magnitude limit of the DPOSS material and covering a wide enough area, the performances of the algorithm were tested on realistically simulated catalogues. The application to a set of 13 CRoNaRio catalogues allowed us to derive a multiplicity function as accurate as those available in literature obtained from redshift surveys.