| Abstract
| - Context. 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. Aims. 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. Methods. We have observed PLCK G004.5−19.5 with GMOS on the 8.1 m-Gemini South Telescope for optical imaging and spectroscopy, and performed a strong lensing analysis. We also searched for associated radio emission in published catalogs. Results. 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 zarc = 1.601. We use LensTool to carry out a strong lensing analysis, from which we measure a median Einstein radius θE( zs = 1.6) ≃ 30″ and estimate an enclosed mass ME = 2.45 -0.47+0.45 × 10 14M⊙. By extrapolating a Navarro-Frenk-White profile, we find a total mass M500SL = 4.0 -1.0+2.1 × 10 14M⊙. We also include a constraint on the mass from previous X-ray observations, which yields a slightly higher mass, M500SL+X = 6.7 -1.3+2.6 × 10 14 M⊙, consistent with the value from strong lensing alone. Intermediate-resolution radio images from the TIFR GMRT Sky Survey at 150 MHz reveal that PLCK G004.5−19.5 hosts a powerful radio relic on scales ≲500 kpc. Emission at the same location is also detected in low-resolution images at 843 MHz and 1.4 GHz. This is one of the higher redshift radio relics known to date.
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