Strong lensing analysis of PLCK G004.5-19.5, a Planck-discovered cluster hosting a radio relic at z = 0.52

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 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^+0.45 × 10¹⁴ M_⊙. By extrapolating a Navarro-Frenk-White profile, we find a total mass M₅₀₀^SL = 4.0_-1.0^+2.1 × 10¹⁴ M_⊙. 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^+2.6 × 10¹⁴ 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.

Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), Comisión Nacional de Investigación Científica y Tecnológica (CONICYT, Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).