2014A&A...562A..43S

The recent discovery of a large number of galaxy clusters using the Sunyaev-Zel'dovich (SZ) effect has opened a new era on the study of the most massive clusters in the Universe. Multiwavelength analyses are required to understand the properties of these new sets of clusters, which are a sensitive probe of cosmology. We aim for a multiwavelength characterization of PLCK G004.5-19.5, one of the most massive X-ray validated SZ effect-selected galaxy clusters discovered by the Planck satellite. We have observed PLCK G004.5-19.5 with GMOS on the 8.1m-Gemini South Telescope for optical imaging and spectroscopy, and performed a strong lensing analysis. We also searched for associated radio emission in published catalogs. An analysis of the optical images confirms that this is a massive cluster, with a dominant central galaxy and an accompanying red sequence of galaxies, plus a 14''-long strong lensing arc. Longslit spectroscopy of six cluster members shows that the cluster is at z=0.516±0.002. We also targeted the strongly lensed arc, and found z_arc=1.601. We use LensTool to carry out a strong lensing analysis, from which we measure a median Einstein radius θ_E(z_s=1.6)≃30'' and estimate an enclosed mass M_E=2.45_–0.47^+0.45x10¹⁴M_☉. By extrapolating a Navarro-Frenk-White profile, we find a total mass M₅₀₀^SL=4.0_–1.0^+2.1x10¹⁴M_☉. We also include a constraint on the mass from previous X-ray observations, which yields a slightly higher mass, M₅₀₀^SL+X=6.7_–1.3^+2.6x10¹⁴M_☉, consistent with the value from strong lensing alone. Intermediate-resolution radio images from the TIFR GMRT Sky Survey at 150MHz reveal that PLCK G004.5-19.5 hosts a powerful radio relic on scales ≲500kpc. Emission at the same location is also detected in low-resolution images at 843MHz and 1.4GHz. This is one of the higher redshift radio relics known to date.