Precise weak lensing constraints from deep high-resolution K_s images: VLT/HAWK-I analysis of the super-massive galaxy cluster RCS2 J 232727.7−020437 at z = 0.70^★

¹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
e-mail: schrabba@astro.uni-bonn.de
² Gemini Observatory, Southern Operations Center, Casilla 603, LaSerena, Chile
³ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
⁴ Université Paris Diderot, AIM, Sorbonne Paris Cité, CEA, CNRS, 91191 Gif-sur-Yvette, France
⁵ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 CA Leiden, The Netherlands
⁶ Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁷ Department of Physics, University of California, Davis, CA 95616, USA
⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA
⁹ Center for Cosmology and Astro-Particle Physics, The Ohio State University, 191 W. Woodruff Ave, Columbus, OH 43210, USA
¹⁰ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
¹¹ Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA
¹² Department of Physics and Astronomy, Tufts University, 574 Boston Avenue, Medford, MA 02155, USA
¹³ Department of Physics and Astronomy, York University, 4700 Keele St., Toronto, Ontario MJ3 1P3, Canada
¹⁴ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA

Received: 7 August 2017
Accepted: 26 October 2017

Abstract

We demonstrate that deep good-seeing VLT/HAWK-I K_s images complemented with g + z-band photometry can yield a sensitivity for weak lensing studies of massive galaxy clusters at redshifts 0.7 ≲ z ≲ 1.1, which is almost identical to the sensitivity of HST/ACS mosaics of single-orbit depth. Key reasons for this good performance are the excellent image quality frequently achievable for K_s imaging from the ground, a highly effective photometric selection of background galaxies, and a galaxy ellipticity dispersion that is noticeably lower than for optically observed high-redshift galaxy samples. Incorporating results from the 3D-HST and UltraVISTA surveys we also obtained a more accurate calibration of the source redshift distribution than previously achieved for similar optical weak lensing data sets. Here we studied the extremely massive galaxy cluster RCS2 J232727.7−020437 (z = 0.699), combining deep VLT/HAWK-I K_s images (point spread function with a 0.′′35 full width at half maximum) with LBT/LBC photometry. The resulting weak lensing mass reconstruction suggests that the cluster consists of a single overdensity, which is detected with a peak significance of 10.1σ. We constrained the cluster mass to M_200c/(10¹⁵ M_⊙) = 2.06_−0.26^+0.28(stat.) ± 0.12(sys.) assuming a spherical Navarro, Frenk & White model and simulation-based priors on the concentration, making it one of the most massive galaxy clusters known in the z ≳ 0.7 Universe. We also cross-checked the HAWK-I measurements through an analysis of overlapping HST/ACS images, yielding fully consistent estimates of the lensing signal.