RedMaPPer Cluster Properties from Two-Dimensional Lensing Shear Maps in the HSC-SSP Survey

TL;DR

This study uses 2D weak-lensing shear maps from the HSC-SSP survey to analyze the properties of galaxy cluster halos, revealing details about their concentration, shape, and centroid offsets, which inform models of dark matter and structure formation.

Contribution

It introduces a 2D weak-lensing analysis of a large cluster sample with elliptical NFW modeling, providing new insights into halo morphology and the concentration-mass relation.

Findings

The concentration-mass relation is steeper than traditional models.

Cluster ellipticity averages around 0.53, indicating moderate elongation.

A bimodal distribution of centroid offsets suggests diverse halo dynamical states.

Abstract

Dark matter halos are fundamental cosmological structures whose properties-such as concentration, ellipticity, and mass centroid-encode information about their formation and evolution. Concentration traces collapse time and internal structure, while ellipticity and centroid offsets reflect halo shape and dynamical state. Accurate characterization of these properties improves mass estimates and tests dark matter models. Gravitational lensing, which directly probes projected mass distributions, provides a powerful means to constrain halo structure. We present a 2D weak-lensing analysis of 299 RedMaPPer clusters using shear measurements from the HSC-SSP first-year data release. By fitting elliptical NFW models with mass priors from the RedMaPPer cluster richness-mass relation, considering the priors helps us break the mass-concentration degeneracy and tighten constraints on other parameters. The derived concentration-mass relation exhibits a slightly steeper slope than traditional weak-lensing power-law or upturn models, and agrees more closely with the results from strong lensing selected halos. More massive and lower-redshift clusters tend to have lower concentrations and appear more spherical. The halo ellipticity distribution is characterized by e=1-b/a=0.530+/-0.168, with a mean of <e>=0.505+/-0.007. We also detect a bimodal distribution in the offsets between optical centers and mass centroids: some halos are well-aligned with their brightest cluster galaxy (BCG), while others show significant displacements. These results highlight the power of 2D weak-lensing modeling in probing halo morphology and in providing key inputs for understanding and modeling systematic effects in stacked lensing analyses.