# A New Dissociative Galaxy Cluster Merger: RM J150822.0+575515.2

**Authors:** Rodrigo Stancioli, David Wittman, Kyle Finner, Faik Bouhrik  
**arXiv:** [2307.10174](https://arxiv.org/abs/2307.10174)  
**Date:** 2023-07-19  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.10174v1/

## Key points

- Study focuses on the discovery and characterization of a new dissociative galaxy cluster merger, RM J150822.0+575515.2 (RMJ1508)
- Researchers aim to investigate mergers that meet specific criteria: binary nature, clear dissociation between gas and galaxies/dark matter, near the plane of the sky
- Discovery method relies on optical and X-ray data, using the redMaPPer catalog as a starting point
- Selection criteria include bimodality, minimum redMaPPer richness of 120, and confirmation through archival X-ray observations
- Multiwavelength observations used to analyze merger scenario, including X-ray properties, galaxy kinematics, weak lensing analysis, simulated analogs for merger parameters reconstruction, radio observations
- Assumptions made regarding cosmological parameters: flat ΛCDM cosmology with H0 = 69.6 km s^-1 Mpc^-1 and Ωm = 0.286
- Cluster is at a redshift of z = 0.54

## Summary

This study focuses on the discovery and characterization of a new dissociative galaxy cluster merger, RM J150822.0+575515.2 (RMJ1508). The researchers aim to investigate mergers that meet specific criteria: being binary (involving only two sub-clusters), exhibiting clear dissociation between gas and galaxies/dark matter, and being near the plane of the sky for easier modeling and understanding of merger dynamics. The discovery method relies on a combination of optical and X-ray data. The redMaPPer catalog is used as a starting point, which contains approximately 25,000 clusters identified using imaging from the Sloan Digital Sky Survey (SDSS). To select for bimodality, the researchers require that the most likely brightest cluster galaxy (BCG) has a probability not exceeding 98% and that the two most likely BCGs have a projected separation of at least 1 arcmin. A minimum redMaPPer richness of 120 is also imposed. Archival X-ray observations are then searched to confirm the merging state with galaxy overdensities straddling the intracluster medium (ICM) gas. RMJ1508 satisfies all these requirements and is selected for further analysis. Multiwavelength observations, both archival and newly acquired, are utilized to elucidate the merger scenario. The paper is organized into several sections: an initial overview based on current literature; analysis of archival XMM-Newton data to derive global X-ray properties; a spectroscopic redshift survey to examine galaxy kinematics; weak lensing analysis through constructing mass maps; deriving merger parameters from simulated analogs to reconstruct the merger scenario; reporting results from radio observations; and presenting conclusions about the merger scenario. Throughout the paper, assumptions are made regarding cosmological parameters, including a flat ΛCDM cosmology with H0 = 69.6 km s^-1 Mpc^-1 and Ωm = 0.286. The cluster is at a redshift of z = 0.54, where 1 arcmin corresponds to 385 kpc. Overall, this study presents an in-depth analysis of a new dissociative galaxy cluster merger that meets specific criteria for accurate modeling and improved understanding of its dynamics. It utilizes multiwavelength observations from both archival sources as well as newly acquired ones in order to elucidate its underlying structure and characteristics such as its cosmological parameters which include H0 = 69.6 km s^-1 Mpc^-1 , Ωm = 0.286 ,and z=0 .54 .