We aim to review the internal structure and dynamics of the Abell 1351 cluster , shown to host a radio halo with a quite irregular shape .
Our analysis is based on radial velocity data for 135 galaxies obtained at the Telescopio Nazionale Galileo .
We combine galaxy velocities and positions to select 95 cluster galaxy members and analyse the internal dynamics of the whole cluster .
We also examine X-ray data retrieved from Chandra and XMM archives .
We measure the cluster redshift , \left < z \right > = 0.325 , the line-of-sight ( LOS ) velocity dispersion , \sigma _ { V } \sim 1500 km s ^ { -1 } , and the X-ray temperature , kT \sim 9 keV .
From both X-ray and optical data independently , we estimate a large cluster mass , in the 1–4 \times 10 ^ { 15 } h _ { 70 } ^ { -1 } M _ { \odot } range .
We attribute the extremely high value of \sigma _ { V } to the bimodality in the velocity distribution .
We find evidence of a significant velocity gradient and optical 3D substructure .
The X-ray analysis also shows many features in favour of a complex cluster structure , probably supporting an ongoing merger of substructures in Abell 1351 .
The observational scenario agrees with the presence of two main subclusters in the northern region , each with its brightest galaxy ( BCG1 and BCG2 ) , detected as the two most important X-ray substructures with a rest-frame LOS velocity difference of \Delta V _ { rf } \sim 2500 km s ^ { -1 } and probably being in large part aligned with the LOS .
We conclude that Abell 1351 is a massive merging cluster .
The details of the cluster structure allow us to interpret the quite asymmetric radio halo as a ‘ normal ’ halo plus a southern relic , strongly supporting a previous suggestion based only on inspection of radio and preliminary X-ray data .