The multiplicity function of galaxies

¹ INAF - Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
² Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Twelve Quays House, Birkenhead CH41 1LD, UK
³ Università di Napoli Federico II, via Cinthia, 80126 Napoli, Italy
⁴ INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
⁵ Department of Physics and Astronomy, Johns Hopkins University, Baltimore – MD, USA

Corresponding author: E. Puddu, puddu@na.astro.it

Received: 21 November 2002
Accepted: 4 February 2003

Abstract

The multiplicity function (MF) of groups and clusters of galaxies is determined using galaxy catalogues extracted from a set of Digitized Palomar Sky Survey (DPOSS) plates. The two different types of structures (of low and high richness) were identified using two different algorithms: a modified version of the van Albada method for groups, and a peak finding algorithm for larger structures. In a 300 deg² area up to , we find 2944 groups and 179 clusters. Our MF covers a wide range of richnesses, from 2 to 200, and the two MFs derived by the two algorithms match smoothly without the need for additional conditions or normalisations. The resulting multiplicity function, of slope , strongly resembles a power law.