Internal dynamics of Abell 2254: a merging galaxy cluster with a clumpy,
  diffuse radio emission
  We explore the internal dynamics of Abell 2254, which has been shown to host
a very clumpy and irregular radio halo. Our analysis is mainly based on
redshift data for 128 galaxies acquired at the TNG. We also use new g',r',i'
photometric data acquired at the INT and (V,i') photometric data available in
the Subaru Archive. X-ray data from the XMM-Newton Science Archive are analyzed
to study the hot gas component. We estimate the cluster redshift <z>=0.177, a
high line-of-sight (LOS) velocity dispersion, sigmaV about 1350 km/s, and X-ray
temperature T about 6.4 keV. Both our optical and X-ray analyses reveal a
complex dynamical activity. The analysis of the 2D galaxy distribution reveals
the presence of two density peaks, one at the East and the other at the West.
Using the full 3D information we detect a high LOS velocity (DeltaV about 3000
km/s), low mass group at the position of the 2D eastern peak. For the main
system we compute a velocity dispersion sigmaV about 1000-1200 km/s. In the
assumption of a bimodal system we estimate a mass M=1.5-2.9 10^15 solar
masses.The X-ray morphological analysis confirms that Abell 2254 is a
dynamically disturbed cluster. The X-ray isophotes are elongated toward the
eastern direction, in agreement with a merger in the post core-crossing phase.
A simple bimodal model finds that data are consistent with a bound, outgoing
subcluster observed a few fractions of Gyr after the core crossing. However,
both optical and X-ray analyses suggest that the main system is, at its time, a
non relaxed structure, indicating N-S as a possible direction for a past
accretion. We conclude that Abell 2254, for its mass and merging structure,
fits well among typical clusters with radio halos. We shortly discuss as the
particular irregularity of the radio halo might be linked to the complexity of
the Abell 2254 structure.
