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%.