Precise Mass Determination of SPT-CL J2106-5844, the Most Massive Cluster at z > 1

Abstract

We present a detailed high-resolution weak-lensing (WL) study of SPT-CL J2106-5844 at z = 1.132, claimed to be the most massive system discovered at z > 1 in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. Based on the deep imaging data from the Advanced Camera for Surveys and Wide Field Camera 3 on-board the Hubble Space Telescope, we find that the cluster mass distribution is asymmetric, composed of a main clump and a subclump ∼640 kpc west thereof. The central clump is further resolved into two smaller northwestern and southeastern substructures separated by ∼150 kpc. We show that this rather complex mass distribution is more consistent with the cluster galaxy distribution than a unimodal distribution as previously presented. The northwestern substructure coincides with the BCG and X-ray peak while the southeastern one agrees with the location of the number density peak. These morphological features and the comparison with the X-ray emission suggest that the cluster might be a merging system. We estimate the virial mass of the cluster to be M 200c = (10.4 +3.3 −3.0 ± 1.0) × 10 14 M , where the second error bar is the systematic uncertainty. Our result confirms that the cluster SPT-CL J2106-5844 is indeed the most massive cluster at z > 1 known to date. We demonstrate the robustness of this mass estimate by performing a number of tests with different assumptions on the centroids, mass-concentration relations, and sample variance.

Multiwavelength view of SPT-CL J2106-5844. The radio galaxies and the thermal and relativistic plasmas in a massive galaxy cluster merger at z~1.13

“…Figure 9 provides a comparative view of the SZ signature of SPT-CL J2106-5844 (both model and dirty image) with the weak lensing and X-ray surface brightness distribution in the cluster. Overall, the SZ effect from SPT-CL J2106-5844 is found to be aligned with the mass distribution measured by Kim et al (2019), with the two subclusters roughly corresponding to the separate clumps in the main mass concentration within the cluster. We observe a moderate offset (> 50 kpc) between the south- .…”

“…7), which strengthens the hypothesis that SPT-CL J2106-5844 is also a merger with two distinct pressure peaks. Furthermore, the overall posterior distribution is similar to the asymmetric distributions seen in the mass and galaxy number density maps (Kim et al 2019). We tested against possible systematics to assess the reliability of this result, and checked that the two SZ components are identified independent of any prior assumptions on the gNFW parameters or point-like component, or of the specific subsets of observations employed in the modelling.…”

“…For reference, we overlay on the hardness ratio map contours from a smoothed version of the X-ray surface brightness image. The asymmetric X-ray brightness distribution hints at the disturbed dynamical state of SPT-CL J2106-5844 (Foley et al 2011;Kim et al 2019).…”

“…Together with the subsequent detection of a very luminous and extended X-ray source by Chandra, the strong SZ significance and the high velocity dispersion of the cluster members hinted at the possibility that SPT-CL J2106-5844 is an exceptionally massive cluster for its redshift. By combining the X-ray, SZ, and velocity dispersion data, Foley et al 2011 estimated the cluster mass to be M 200 = (1.27 ± 0.21) • 10 15 M , implying at the time it was the most massive 1 singular, virialized object known at z > 1 (see also Amodeo et al 2016, Schrabback et al 2018, Bulbul et al 2019, and Kim et al 2019, and the present work for further independent mass estimates for this system; we note that the assumption made in several previous studies that this system can be described by a single mass component could present a critical source of bias, given the clear evidence for two subclusters we present in this work).…”

A massive blow for ΛCDM – the high redshift, mass, and collision velocity of the interacting galaxy cluster El Gordo contradicts concordance cosmology

“…The most massive cluster at z > 1 is SPT-CL J2106-5844, with z = 1.132 +0.002 −0.003 and mass M200 = (1.27 ± 0.21) × 10 15 M (Foley et al 2011). This was confirmed by the more recent study of Kim et al (2019), which gives a slightly lower mass estimate of M200 = 1.04 +0.33 −0.30 × 10 15 M . Their figure 6 shows two weak lensing peaks, indicating the system is likely a merger product.…”