Clash: Precise New Constraints on the Mass Profile of the Galaxy Cluster A2261

We precisely constrain the inner mass profile of A2261 (z = 0.225) for the first time and determine that this cluster not “overconcentrated” as found previously, implying a formation time in agreement with ΛCDM expectations. results are based on multiple strong-lensing analyses of new 16-band Hubble Space Telescope imaging as part of the Cluster Lensing and Supernova survey with Hubble. Combining this with revised weaklensing of Subaru wide-field imaging with five-band Subaru + KPNO photometry, we place tight new on the halo virial mass Mvir = (2.2 ± 0.2) × 1015 M h−1 70 (within rvir ≈ 3 Mpc h−1 70 ) and concentration = 6.2 ± 0.3 when assuming a spherical halo. This agrees broadly with average c(M, z) predictions from recent ΛCDM simulations, which span 58. Our most significant systematic uncertainty is halo elongation the line of sight (LOS). To estimate this, we also derive a mass profile based on archival Chandra X-ray and find it to be ∼35% lower than our lensing-derived profile at r2500 ∼ 600 kpc. Agreement can achieved by a halo elongated with a ∼2:1 axis ratio along our LOS. For this elongated halo model, we find = (1.7 ± 0.2) × 1015 M h−1 70 and cvir = 4.6 ± 0.2, placing rough lower limits on these values. The need halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec redshifts and find that these tend to lower Mvir further by ∼7% and increase cvir by ∼5%.