CLASH: Weak-Lensing Shear-and-Magnification Analysis of 20 Galaxy Clusters (1404.1375v3)

Abstract: We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19<z<0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ~25 in the radial range of 200 to 3500kpc/h. The stacked tangential-shear signal is well described by a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of $c_{200c}=4.01^{+0.35}_{-0.32}$ at $M_{200c}=1.34^{+0.10}_{-0.09} 10^{15}M_{\odot}$. We show this is in excellent agreement with Lambda cold-dark-matter (LCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is $\alpha_E=0.191^{+0.071}_{-0.068}$, which is consistent with the NFW-equivalent Einasto parameter of $\sim 0.18$. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data, and measure cluster masses at several characteristic radii. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the LCDM model.

CLASH: Weak-Lensing Shear-and-Magnification Analysis of 20 Galaxy Clusters

The analysis conducted by Umetsu et al. provides a comprehensive examination of 20 galaxy clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) using weak-lensing techniques. The paper focuses on understanding the mass distribution within these galaxy clusters by employing both shear and magnification methods, key components of gravitational lensing.

Overview and Methodology

The research utilizes a sample comprising 16 X-ray-selected clusters and 4 known for high lensing magnification properties, spanning a redshift range of 0.19 < z < 0.69. The primary data is sourced from the Suprime-Cam wide-field imager on the Subaru Telescope, allowing for high-resolution imaging necessary for accurate weak-lensing measurements.

The paper extensively adapts the shear-and-magnification analysis across this sample to reconstruct the mass distribution profiles. For each cluster, the azimuthally-averaged tangential shear and magnification bias profiles are computed to evaluate the density profile. A Bayesian approach is integrated into the analysis to account for uncertainties in redshift distributions of background galaxies, which influence the shear and magnification estimates.

Key Findings

1. Shear-Only vs. Shear + Magnification Analysis: The paper found that combining shear with magnification measurements provided a 10% improvement in statistical accuracy over shear-only methods.
2. Average Mass Distribution: The ensemble-averaged tangential shear profile from the 16 X-ray-selected clusters yielded a strong detection (signal-to-noise ratio ~25) over a radial range of 200 to 3500 kpc/h, which allowed probing of the halo profile accurately.
3. Mass Concentration Relation: The data indicates that the Navarro-Frenk-White (NFW) profile fits well, with a mean concentration parameter c_200c of 4.01 at a halo mass M_200c of 1.34 x 10^15 M_☉. This result aligns with predictions from ΛCDM simulations, particularly when accounting for CLASH X-ray selection functions and projection effects.
4. Influence of Large-Scale Structure: The mass profiles of individual clusters were reconstructed, showing consistency between observed profiles and model predictions when considering both one-halo and two-halo terms. This demonstrates the significance of surrounding large-scale structures in interpreting lensing data.
5. Consistency with Cosmological Models: The results were consistent with theoretical predictions from ΛCDM models, especially with non-radiative simulations that include baryonic effects. The calculated concentration values were marginally higher than, but statistically compatible with, certain previous numerical simulations based on dark matter.

Implications and Future Directions

The implications of this paper are substantial for cosmological inquiries, considering that galaxy clusters are pivotal for probing the universe’s structure and evaluating cosmological models. The findings validate the use of combined shear and magnification techniques as powerful tools for mass reconstruction in gravitational lensing analyses. The consistent concordance of observational results with ΛCDM predictions reaffirms current theoretical constructs of dark matter-dominated structures.

This paper sets a precedent for future works to adopt multi-probe strategies harnessing both ground-based and space-based observational capabilities for comprehensive cluster analyses. It calls for further exploration into understanding cluster dynamism, substructure impacts, and potential deviations from standard cosmological models through enlarged samples and refined methods.

The research underscores the necessity to correlate lensing data with other observational domains like X-ray and Sunyaev-Zel'dovich effect data, fostering a holistic framework toward understanding the cosmos's cold dark matter scaffolding. As computational techniques and survey capabilities evolve, analyzing larger and more diverse cluster samples will contribute to resolving persistent questions regarding dark matter’s nature and distribution.