We present the study of the internal dynamics of the intriguing galaxy cluster Abell 1703 , a system hosting a probable giant radio halo whose dynamical status is still controversial .
Our analysis is based on unpublished spectroscopic data acquired at the Italian Telescopio Nazionale Galileo and data publicly available in the literature .
We also use photometric data from the Sloan Digital Sky Survey .
We select 147 cluster members and compute the cluster redshift \left < z \right > \sim 0.277 and the global line-of-sight velocity dispersion \sigma _ { v } \sim 1300 km s ^ { -1 } .
We infer that Abell 1703 is a massive cluster : M _ { 200 } \sim 1 - 2 \times 10 ^ { 15 } M _ { \odot } .
The results of our study disagree with the picture of an unimodal , relaxed cluster as suggested by previous studies based on the gravitational lensing analysis and support the view of a perturbed dynamics proposed by recent works based on Chandra X-ray data .
The first strong evidence of a dynamically disturbed cluster comes from the peculiarity of the BCG velocity with respect to the first moment of the velocity distribution of member galaxies .
Moreover , several statistical tests employed to study the cluster galaxies kinematics find significant evidence of substructure , being Abell 1703 composed by at least two or three subclumps probably caught after the core-core passage .
In this observational scenario , the suspected existence of a radio halo in the centre of this cluster is not surprising and well agrees with the theoretical models describing diffuse radio sources in clusters .