Mass, light and colour of the cosmic web in the supercluster SCL2243-0935 (z = 0.447)^⋆,⋆⋆

¹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
e-mail: mischa@astro.uni-bonn.de
² Isaac Newton Group of Telescopes, Calle Alvarez Abreu 70, 38700 Santa Cruz de La Palma, Spain
³ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 Leiden, The Netherlands
⁴ Department of Physics and Astronomy, 6224 Agricultural Road, University of British Columbia, Vancouver, Canada

Received: 17 December 2010
Accepted: 31 March 2011

Abstract

Aims. In archival 2.2 m MPG-ESO/WFI data we discovered several mass peaks through weak gravitational lensing, forming a possible supercluster at redshift 0.45. Through wide-field imaging and spectroscopy we aim to identify the supercluster centre, confirm individual member clusters, and detect possible connecting filaments.

Methods. Through multi-colour imaging with CFHT/Megaprime and INT/WFC we identify a population of early-type galaxies and use it to trace the supercluster network. EMMI/NTT multi-object spectroscopy is used to verify the initial shear-selected cluster candidates. We use weak gravitational lensing to obtain mass estimates for the supercluster centre and the filaments.

Results. We identified the centre of the SCL2243-0935 supercluster, MACS J2243-0935, which was found independently by Ebeling et al. (2001, 2010). We found 13 more clusters or overdensities embedded in a large filamentary network. Spectroscopic confirmation for about half of them is still pending. Three  Mpc filaments are detected, and we estimate the global size of SCL2243 to be  Mpc, making it one of the largest superclusters known at intermediate redshifts. Weak lensing yields  Mpc and M₂₀₀ = (1.54 ± 0.29) × 10¹⁵   M_⊙ for MACS J2243 with M/L = 428 ± 82, very similar to results from size-richness cluster scaling relations. Integrating the weak lensing surface mass density over the supercluster network (defined by increased i-band luminosity or g − i colours), we find (1.53 ± 1.01) × 10¹⁵   M_⊙ and M/L = 305 ± 201 for the three main filaments, consistant with theoretical predictions. The filaments’ projected dimensionless surface mass density κ varies between 0.007 − 0.012, corresponding to ρ/ρ_crit = 10 − 100 depending on location and de-projection. The greatly varying density of the cosmic web is also reflected in the mean colour of galaxies, e.g.  ⟨ g − i ⟩  = 2.27 mag for the supercluster centre and 1.80 mag for the filaments.

Conclusions. SCL2243 is significantly larger and much more richly structured than other known superclusters such as A901/902 or MS0302 studied with weak lensing before. It is a text-book supercluster with little contamination along the line of sight, making it a perfect sandbox for testing new techniques probing the cosmic web.