Hubble Space Telescope Combined Strong and Weak Lensing Analysis of the CLASH Sample: Mass and Magnification Models and Systematic Uncertainties (1411.1414v4)

Abstract: We present results from a comprehensive lensing analysis in HST data, of the complete CLASH cluster sample. We identify new multiple-images previously undiscovered allowing improved or first constraints on the cluster inner mass distributions and profiles. We combine these strong-lensing constraints with weak-lensing shape measurements within the HST FOV to jointly constrain the mass distributions. The analysis is performed in two different common parameterizations (one adopts light-traces-mass for both galaxies and dark matter while the other adopts an analytical, elliptical NFW form for the dark matter), to provide a better assessment of the underlying systematics - which is most important for deep, cluster-lensing surveys, especially when studying magnified high-redshift objects. We find that the typical (median), relative systematic differences throughout the central FOV are $\sim40\%$ in the (dimensionless) mass density, $\kappa$, and $\sim20\%$ in the magnification, $\mu$. We show maps of these differences for each cluster, as well as the mass distributions, critical curves, and 2D integrated mass profiles. For the Einstein radii ($z_{s}=2$) we find that all typically agree within $10\%$ between the two models, and Einstein masses agree, typically, within $\sim15\%$. At larger radii, the total projected, 2D integrated mass profiles of the two models, within $r\sim2\arcmin$, differ by $\sim30\%$. Stacking the surface-density profiles of the sample from the two methods together, we obtain an average slope of $d\log (\Sigma)/d\log(r)\sim-0.64\pm0.1$, in the radial range [5,350] kpc. Lastly, we also characterize the behavior of the average magnification, surface density, and shear differences between the two models, as a function of both the radius from the center, and the best-fit values of these quantities.

Overview of the Hubble Space Telescope Combined Strong and Weak Lensing Analysis of the CLASH Sample

The paper presents a meticulous lensing analysis of the complete Cluster Lensing And Supernova survey with Hubble (CLASH) cluster sample, emphasizing the significance of unveiling mass distributions and magnification maps based on Hubble Space Telescope (HST) data. The essence of this research resides in integrating both strong-lensing (SL) and weak-lensing (WL) constraints to meticulously refine the mass models of 25 galaxy clusters. This work is notably centered on addressing model systematics by employing two different modelling parameterizations, highlighting the implications for deep, cluster-lensing surveys, especially those probing the magnified high-redshift Universe.

Key Numerical Findings and Implications

A notable achievement of the analysis is the identification of numerous new multiple-image systems, allowing enhanced constraints on the mass profiles of the observed clusters. The findings underline that systematic differences in mass density ($\kappa$) and magnification ($\mu$) maps, when examined through distinct models, manifest typical median discrepancies of approximately 40% and 20%, respectively, across the field-of-view (FOV). The paper further reveals that Einstein radii for $z_s = 2$ agree within 10% between models, highlighting a minor discrepancy in total masses enclosed within these radii, estimated at around 15%.

Interestingly, the authors present the critical interpretation that such differences stem from inherent model degeneracies, specifically the ellipticity degeneracy, which cannot be readily broken by current SL and WL data alone. They speculate that external constraints on magnification or relative magnifications among multiple images might offer resolution pathways for certain degeneracies. The findings explicitly emphasize that the mass profiles derived from these models play pivotal roles in assessing concentration-mass (c-M) relations and other cosmological parameters, with direct repercussions for structure formation studies in the $\Lambda$CDM paradigm.

Theoretical and Practical Implications

The paper extends its implications by addressing systematic uncertainties, a vital aspect for lensing models used in magnification studies of high-redshift galaxies or for predicting lensed volumes. With the onset of campaigns like the Hubble Frontier Fields (HFF), understanding these systematics becomes increasingly vital for reliable magnification estimates, reflected in this research’s insights into differences between parametrizations such as Light-Traces-Mass (LTM) and PIEMDeNFW.

The future developments speculated by the authors dwell on aligning lensing models with independent mass profile measurements from wider-field WL analyses or contrasting them against numerical simulations, revisiting the overall statistical properties of the CLASH sample. The paper’s suggestion of correspondence between two different methods to probe systematics sets a standard for upcoming examinations in lensing, particularly with upcoming deep-field surveys.

Future Directions

As a comprehensive analysis, this research opens pathways for the community to build upon these CLASH lens models, leveraging updated spectroscopic redshifts and potential additional HST data. It paves the way for continual refinement of mass and magnification predictions, crucial for understanding high-redshift galaxy clusters and the underlying cosmic structure. The release of these refined models to the public domain through the Mikulski Archive for Space Telescopes (MAST) exemplifies the collaborative spirit intended to propel this research's utility within the astronomical community.

In summation, the insights gained from this thorough analysis provide a crucial stepping stone for subsequent studies aimed at harnessing the immense potential of cluster lenses in cosmological research, notably enhancing the reliability of lensing models amidst a landscape of burgeoning observational data. The paper stands as a testament to precision cosmology, embracing both innovation in method and collaboration in utility.