ALBERT

Beschreibung: 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, 〈 z 〉 = 0.325, the line-of-sight (LOS) velocity dispersion, V  ~ 1500 km s –1 , and the X-ray temperature, kT  ~ 9 keV. From both X-ray and optical data independently, we estimate a large cluster mass, in the 1–4 $\times 10^{15}\;h_{70}^{-1}\;\rm{M}_{{\odot }} \;$ range. We attribute the extremely high value of 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 V rf  ~ 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.

Beschreibung: We analyse the dynamical state of Abell 1914, a merging cluster hosting a radio halo, quite unusual for its structure. Our study considers spectroscopic data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo. We select 89 cluster members from spatial and velocity distributions. We also use photometry Canada–France–Hawaii Telescope archives. We compute the mean cluster redshift, 〈 z 〉 = 0.168, and the velocity dispersion which shows a high value, V = 1210 ${^{+ 125}_{- 110}}$  km s –1 . From the 2D analysis we find that Abell 1914 has a north-east (NE)–south-west (SW) elongated structure with two galaxy clumps, that mostly merge in the plane of the sky. Our best but very uncertain estimate of the velocity dispersion of the main system is V , main  ~ 1000 km s –1 . We estimate a virial mass M sys  = 1.4–2.6 x 10 15 h ${^{- 1}_{70}}$ M for the whole system. We study the merger through a simple two-body model and find that data are consistent with a bound, outgoing substructure observed just after the core crossing. By studying the 2D distribution of the red galaxies, photometrically selected, we show that Abell 1914 is contained in a rich large-scale structure, with two close companion galaxy systems, known to be at z  ~ 0.17. The system at SW supports the idea that the cluster is accreting groups from a filament aligned in the NE–SW direction, while that at NW suggests a second direction of the accretion (NW–SE). We conclude that Abell 1914 well fits among typical clusters with radio haloes. We argue that the unusual radio emission is connected to the complex cluster accretion and suggest that Abell 1914 resembles the well-known nearby merging cluster Abell 754 for its particular observed phenomenology.