Precise weak lensing constraints from deep high-resolution $K_{\mathrm{s}}$ images: VLT/HAWK-I analysis of the super-massive galaxy cluster RCS2$J$232727.7$-$020437 at $z=0.70$

Abstract

We demonstrate that deep good-seeing VLT/HAWK-I $K_{\mathrm{s}}$ images complemented with $g$+$z$-band photometry can yield a sensitivity for weak lensing studies of massive galaxy clusters at redshifts \mbox{$0.7\lesssim z\lesssim 1.1$}, 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 $K_{\mathrm{s}}$ 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$J$232727.7$-$020437 (\mbox{$z=0.699$}), combining deep VLT/\mbox{HAWK-I} $K_{\mathrm{s}}$ images (point spread function with a 0\farcs35 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 $10.1\ddot{I}ƒ$. We constrained the cluster mass to \mbox{$M_{200c}/(10^{15}{\mathrm{M}}_{\odot })=2.06_{-0.26}^{+0.28}(stat.)\pm 0.12(sys.)$} 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 \mbox{$z\gtrsim 0.7$} 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.

17 pages, 14 figures, 1 table. Matches the version published in A&A. Includes minor changes to the text and corrections from the language editor