Line-of-sight Elongation and Hydrostatic Mass Bias of the Frontier Fields Galaxy Cluster Abell 370

Keiichi Umetsu; Shutaro Ueda; Bau-Ching Hsieh; Mario Nonino; I-Non Chiu; Masamune Oguri; Sandor M. Molnar; Anton M. Koekemoer; Sut-Ieng Tam

doi:10.3847/1538-4357/ac7a9e

paper

Line-of-sight Elongation and Hydrostatic Mass Bias of the Frontier Fields Galaxy Cluster Abell 370

arXiv:2203.03647 · doi:10.3847/1538-4357/ac7a9e

Abstract

We present a detailed weak-lensing and X-ray study of the Frontier Fields galaxy cluster Abell 370, one of the most massive known lenses on the sky, using wide-field BRz Subaru/Sprime-Cam and Chandra X-ray observations. By combining two-dimensional (2D) shear and azimuthally averaged magnification constraints derived from Subaru data, we perform a lensing mass reconstruction in a free-form manner, which allows us to determine both radial structure and 2D morphology of the cluster mass distribution. In a triaxial framework assuming a Navarro-Frenk-White density profile, we constrain the intrinsic structure and geometry of the cluster halo by forward modeling the reconstructed mass map. We obtain a halo mass $M_{200} = (1.54 \pm 0.29) \times 1 0^{15} h^{- 1} M_{⊙}$ , a halo concentration $c_{200} = 5.27 \pm 1.28$ , and a minor-major axis ratio $q_{a} = 0.62 \pm 0.23$ with uninformative priors. Using a prior on the line-of-sight alignment of the halo major axis derived from binary merger simulations constrained by multi-probe observations, we find that the data favor a more prolate geometry with lower mass and lower concentration. From triaxial lens modeling with the line-of-sight prior, we find a spherically enclosed gas mass fraction of $f_{gas} = (8.4 \pm 1.0) %$ at $0.7 h^{- 1}$ Mpc $\sim 0.7 r_{500}$ . When compared to the hydrostatic mass estimate from Chandra observations, our triaxial weak-lensing analysis yields spherically enclosed mass ratios of $1 - b \equiv M_{HE} / M_{WL} = 0.56 \pm 0.09$ and $0.51 \pm 0.09$ at $0.7 h^{- 1}$ Mpc with and without using the line-of-sight prior, respectively. Since the cluster is in a highly disturbed dynamical state, this represents the likely maximum level of hydrostatic bias in galaxy clusters.

Version accepted by ApJ; 26 pages (main body) + 8 pages (appendices and references), 20 figures, 9 tables

Line-of-sight Elongation and Hydrostatic Mass Bias of the Frontier Fields Galaxy Cluster Abell 370

Abstract

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