Internal dynamics of the radio-halo cluster A2219: A multi-wavelength analysis

We present the results of the dynamical analysis of the rich, hot, and X-ray very luminous galaxy cluster A2219, containing a powerful diffuse radio-halo. Our analysis is based on new redshift data for 27 galaxies in the cluster region, measured from spectra obtained at the TNG, with the addition of other 105 galaxies recovered from reduction of CFHT archive data in a cluster region of ~$5\arcmin$ radius (~$ 0.8$ h-1 Mpc $ \;$at the cluster distance) centered on the cD galaxy. The investigation of the dynamical status is also performed using X-ray data stored in the Chandra archive. Further, valuable information comes from other bands – optical photometric, infrared, and radio data – which are analyzed and/or discussed, too. We find that A2219 appears as a peak in the velocity space at $z=0.225$, and select 113 cluster members. We compute a high value for the line-of-sight velocity dispersion, $\sigma_{\rm v}= 1438^{+109}_{-86}$ km s-1, consistent with the high average X-ray temperature of 10.3 keV. If dynamical equilibrium is assumed, the virial theorem leads to $M\sim2.8\times 10^{15}$ $h^{-1} \ M_{\odot} \;$for the global mass within the virial region. However, further investigation based on both optical and X-ray data shows significant signs of a young dynamical status. In fact, we find strong evidence for the elongation of the cluster in the SE-NW direction coupled with a significant velocity gradient, as well as for the presence of substructure both in optical data and X-ray data. Moreover, we point out the presence of several active galaxies. We discuss the results of our multi-wavelength investigation suggesting a complex merging scenario where the main, original structure is subject to an ongoing merger with a few clumps aligned in a filament in the foreground oriented in an oblique direction with respect to the line-of-sight. Our conclusion supports the view of the connection between extended radio emission and merging phenomena in galaxy clusters.