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.
Highlights
Radio relics, known as cluster radio shocks, refer to megaparsec-scale diffuse synchrotron radio emission features observed in the outskirts of merging galaxy clusters
We reduced the MMT/Hectospec observations with the HSRED v2.1 pipeline12 provided by the Telescope Data Center (TDC) at SAO, originally written by Richard Cool
Because some residue from the krypton light leak is still evident in the TDC-cleaned spectra, we provided a list of masked regions for the residual to estimate redshifts more reliably
Summary
Known as cluster radio shocks, refer to megaparsec-scale diffuse synchrotron radio emission features observed in the outskirts of merging galaxy clusters. With deep Very Large Array (VLA) observations at 20 cm (1.4 GHz) and 90 cm (325 MHz), Bonafede et al (2009) confirmed the presence of the two radio relics in A1240 and firmly detected a spectral index flattening toward the cluster outskirts in the northern relic, which is consistent with our expectation if the relic traces the merger shock traveling to the north.
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