Multiwavelength Analysis of A1240, the Double Radio-relic Merging Galaxy Cluster Embedded in an ∼80 Mpc-long Cosmic Filament

Abstract

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 an ∼4 Mpc filamentary structure elongated in a north–south orientation. The northern ( M 200 = 2.61 − 0.60 + 0.51 × 10 14 M ⊙ ) and middle ( M 200 = 1.09 − 0.43 + 0.34 × 10 14 M ⊙ ) mass clumps separated by ∼1.3 Mpc are associated with A1240 and colocated 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 × 10 14 M ⊙ ), ∼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 postmerger binary system in the returning phase with a time since collision of ∼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.