CLASH: PRECISE NEW CONSTRAINTS ON THE MASS PROFILE OF THE GALAXY CLUSTER A2261

Abstract

We precisely constrain the inner mass profile of A2261 (z = 0.225) for the first time and determine that this cluster
\nis not “overconcentrated” as found previously, implying a formation time in agreement with ΛCDM expectations.
\nThese results are based on multiple strong-lensing analyses of new 16-band Hubble Space Telescope imaging
\nobtained as part of the Cluster Lensing and Supernova survey with Hubble. Combining this with revised weaklensing
\nanalyses of Subaru wide-field imaging with five-band Subaru + KPNO photometry, we place tight new
\nconstraints on the halo virial mass Mvir = (2.2 ± 0.2) × 1015 M h−1
\n70 (within rvir ≈ 3 Mpc h−1
\n70 ) and concentration
\ncvir = 6.2 ± 0.3 when assuming a spherical halo. This agrees broadly with average c(M, z) predictions from recent
\nΛCDM simulations, which span 58. Our most significant systematic uncertainty is halo elongation
\nalong the line of sight (LOS). To estimate this, we also derive a mass profile based on archival Chandra X-ray
\nobservations and find it to be ∼35% lower than our lensing-derived profile at r2500 ∼ 600 kpc. Agreement can
\nbe achieved by a halo elongated with a ∼2:1 axis ratio along our LOS. For this elongated halo model, we find
\nMvir = (1.7 ± 0.2) × 1015 M h−1
\n70 and cvir = 4.6 ± 0.2, placing rough lower limits on these values. The need
\nfor halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic
\nerrors in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec
\nspectroscopic redshifts and find that these tend to lower Mvir further by ∼7% and increase cvir by ∼5%.
\nKe