The red-sequence of 72 WINGS local galaxy clusters

¹ Astronomy DepartmentUniversity of Padova, Vicolo Osservatorio 2, 35122 Padova, Italy
² INAF – Padova Astronomical Observatory, Vicolo Osservatorio 5, 35122 Padova, Italy
e-mail: bianca.poggianti@oapd.inaf.it
³ INAF – Trieste Astronomical Observatory, via Tiepolo 11, 34131 Trieste, Italy
⁴ Sterrenkundig Observatorium Vakgroep Fysica en Sterrenkunde Universeit Gent, Gent, Belgium
⁵ Centro de Estudios de Física del Cosmos de Aragón, Plaza de San Juan 1, 44001 Teruel, Spain
⁶ Centre for Astrophysics & Supercomputing, Swinburne University, Hawthorn 3122, VIC, Australia
⁷ Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101, USA
⁸ The Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁹ Departamento de Astrofisica, Universidad Complutense de Madrid, Spain

Received: 20 June 2011
Accepted: 16 September 2011

Abstract

We study the color − magnitude red sequence and blue fraction of 72 X-ray selected galaxy clusters at z = 0.04−0.07 from the WINGS survey, searching for correlations between the characteristics of the red sequence (RS) and the environment. We consider the slope and scatter of the red sequence, the number ratio of red luminous-to-faint galaxies, the blue fraction, and the fractions of ellipticals, S0s, and spirals that compose the RS. None of these quantities correlate with the cluster velocity dispersion, X-ray luminosity, number of cluster substructures, BCG prevalence over next brightest galaxies, and the spatial concentration of ellipticals. The properties of the RS, instead, depend strongly on local galaxy density. Higher density regions have a smaller RS scatter, a higher luminous-to-faint ratio, a lower blue fraction, and a lower spiral fraction on the RS. Our results clearly illustrate the prominent effect of the local density in setting the epoch when galaxies become passive and join the red sequence, as opposed to the mass of the galaxy host structure.