Hubble flow around Fornax cluster of galaxies^⋆

¹ Université de Nice – Sophia Antipolis, Observatoire de la Côte d’Azur Laboratoire Cassiopée, UMR 6202, BP-4229, 06304 Nice Cedex 4, France
e-mail: phiruzi@gmail.com
² Special Astrophysical Observatory of the Russian Academy of Sciences Laboratory of Extragalactic Astrophysics and Cosmology Nizhnij Arkhyz, 369167, Karachay-Cherkessia, Russia
³ Université de Lyon, Université Lyon 1, CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, 69622 Villeurbanne, France

Received: 26 October 2010
Accepted: 1 June 2011

Abstract

Aims. This work aims to provide a new mass estimate for the Fornax cluster and the Fornax-Eridanus complex, avoiding methods like the virial or fits of the X-ray emission profile, which assume that the system is in equilibrium. This is probably not the case for Fornax, because it is still in process of formation.

Methods. Our mass estimate is based on determination of the zero-velocity surface, which, in the context of the spherical infall model, permits an evaluation of the total mass inside such a surface. The zero-velocity surface radius R₀ was estimated either by a running median procedure or by fitting the data to the velocity field expected from the spherical model, including effects of the cosmological constant. The velocity field in a region within 20 Mpc of the Fornax center was mapped using a list of 109 galaxies whose distances have an average accuracy of 0.31 mag in their distance modulus.

Results. Our analysis indicates that the mass of the Fornax cluster itself is  [0.40−3.32] × 10¹⁴   M_⊙ inside a radius of  [2.62−5.18] Mpc while the mass inside  [3.88−5.60] Mpc, corresponding to the Fornax-Eridanus complex, is  [1.30−3.93] × 10¹⁴   M_⊙.