Multiwavelength Analysis of A1240, the Double Radio Relic Merging Galaxy Cluster Embedded in a ~80 Mpc-long Cosmic Filament

TL;DR

This study combines multiwavelength observations to analyze the merging galaxy cluster A1240, revealing its complex structure, mass distribution, and filamentary environment, and suggests it is a post-merger system approximately 1.7 billion years after collision.

Contribution

It provides a comprehensive multiwavelength analysis of A1240, including weak lensing, X-ray, and radio data, revealing its merger history and large-scale filamentary context.

Findings

A1240 consists of three mass clumps aligned in a filament.

The cluster is a post-merger system with a collision ~1.7 Gyr ago.

Embedded in an 80 Mpc filament aligned with the merger axis.

Abstract

We present a multiwavelength study of the double radio relic cluster A1240 at z=0.195. Our Subaru-based weak lensing analysis detects three mass clumps forming a ~4 Mpc filamentary structure elongated in the north-south orientation. The northern ($M_{200}=2.61_{-0.60}^{+0.51}\times10^{14} M_{\odot}$) and middle ($M_{200}=1.09_{-0.43}^{+0.34}\times10^{14} M_{\odot}$) mass clumps separated by ~1.3 Mpc are associated with A1240 and co-located with the X-ray peaks and cluster galaxy overdensities revealed by Chandra and MMT/Hectospec observations, respectively. The southern mass clump ($M_{200}=1.78_{-0.55}^{+0.44}\times10^{14} M_{\odot}$), ~1.5 Mpc to the south of the middle clump, coincides with the galaxy overdensity in A1237, the A1240 companion cluster at z=0.194. Considering the positions, orientations, and polarization fractions of the double radio relics measured by the LOFAR study, we suggest that A1240 is a post-merger binary system in the returning phase with the time-since-collision ~1.7 Gyr. With the SDSS DR16 data analysis, we also find that A1240 is embedded in the much larger-scale (~80 Mpc) filamentary structure whose orientation is in remarkable agreement with the hypothesized merger axis of A1240.