# LoCuSS: First Results from Strong-lensing Analysis of 20 Massive Galaxy Clusters at z~0.2

**Authors:** Johan Richard, Graham P. Smith, Jean-Paul Kneib, Richard Ellis, Alastair J. R. Sanderson, Liuyi Pei, Thomas Targett, David Sand, Mark Swinbank, Helmut Dannerbauer, Pasquale Mazzotta, Marceau Limousin, Eiichi Egami, Eric Jullo, Victoria Hamilton-Morris, Sean Moran  
**arXiv:** [0911.3302](https://arxiv.org/abs/0911.3302)  
**Date:** 2009-11-17  
**Summary page:** https://www.summarizepaper.com/en/paper/0911.3302v2/

## Key points

- Statistical analysis of 20 strong lensing clusters from the LoCuSS survey
- Utilization of Hubble Space Telescope imaging and Keck-I telescope spectroscopic observations
- Investigation of mass distribution and substructures within the clusters
- Measurement of total cluster mass and fraction associated with substructures within 250 kpc radius
- Comparison with baryon distribution in cores traced by old stellar populations and X-ray emitting intracluster medium
- Distribution of Einstein radii follows a log-normal distribution with peak at <log(RE(z=2))> = 1.16 +/- 0.28
- X-ray/lensing mass discrepancy (<M_SL/M_X>) of 1.3 at a 3 sigma significance level, greater in clusters with larger substructure fractions indicating departures from hydrostatic equilibrium
- Correlation between cluster substructure fraction and slope of gas density profile on small scales suggesting connection between cluster-cluster mergers and gas cooling processes
- Cluster-cluster mergers play important role in shaping properties of cluster cores, potentially disturbing cool cores
- No evidence to support recent claims challenging Cold Dark Matter (CDM) paradigm based on large Einstein radius clusters
- Insights into understanding evolution of strong lensing clusters and influence of cluster-cluster mergers on their properties

## Summary

In this study, the authors present a statistical analysis of 20 strong lensing clusters from the Local Cluster Substructure Survey (LoCuSS). They utilize high-resolution Hubble Space Telescope imaging and follow-up spectroscopic observations using the Keck-I telescope to investigate the mass distribution and substructures within these clusters. The researchers employ detailed parameterized models to measure the total cluster mass and fraction of that mass associated with substructures within a radius of less than 250 kiloparsecs (kpc). They compare these measurements with the distribution of baryons in the cores, as traced by old stellar populations and the X-ray emitting intracluster medium. The main findings of this analysis include several significant results. Firstly, they observe that the distribution of Einstein radii follows a log-normal distribution with a peak at <log(RE(z=2))> = 1.16 +/- 0.28. Secondly, they detect an X-ray/lensing mass discrepancy (<M_SL/M_X>) of 1.3 at a 3 sigma significance level which is found to be greater in clusters with larger substructure fractions indicating departures from hydrostatic equilibrium. Furthermore, there is a correlation between cluster substructure fraction and the slope of gas density profile on small scales suggesting a connection between cluster-cluster mergers and gas cooling processes within these systems. Overall, these results support the notion that cluster-cluster mergers play an important role in shaping the properties of cluster cores leading to departures from hydrostatic equilibrium and potentially disturbing cool cores. Importantly, this study does not provide evidence to support recent claims challenging the Cold Dark Matter (CDM) paradigm based on large Einstein radius clusters. In summary, this research provides valuable insights into understanding how strong lensing clusters evolve and highlights the influence of cluster-cluster mergers on their properties. These findings contribute to our understanding of galaxy cluster formation and dynamics within CDM framework.