| 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 \hbox{$(5{-}15)\,h_{70}^{-1}$}(5−15)h70-1 Mpc filaments are detected, and we estimate the global size of SCL2243 to be \hbox{$45\times15\times50\,h_{70}^{-1}$}45×15×50h70-1 Mpc, making it one of the largest superclusters known at intermediate redshifts. Weak lensing yields \hbox{$r_{200}=(2.06\pm0.13)\,h_{70}^{-1}$}r200=(2.06±0.13)h70-1 Mpc and M200 = (1.54 ± 0.29) × 10 15 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) × 10 15 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/ ρcrit = 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.
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