The dynamical state of galaxy clusters containing wide-angle tailed (WAT) radio galaxies is explored. These galaxies produce twin jets of plasma which abruptly decollimate and bend into a V-shape morphology. A likely mechanism for the bending of the jets is ram pressure from the hot ICM (intracluster medium). The dynamical state of the cluster is related to the bending problem in that either the WAT galaxy should have a substantial peculiar motion with respect to the cluster, or the ICM is in motion because of the ongoing formation of the cluster. The dynamics of clusters is probed using the radial velocities and positions of cluster member galaxies, and the surface brightness distribution of X-rays produced by the hot (10^7 K) cluster gas. The radial velocities are obtained through multifiber spectroscopy. The X-ray observations are made with the ROSAT X-ray satellite. Diagnostics for substructure (i.e., artifacts of merger) are both created and culled from the literature. The effectiveness of these diagnostics are analyzed by applying them to N-body simulations of cluster-subcluster mergers. A battery of complementary tests is recommended. Next, these diagnostics are applied to WAT clusters. Several likely cases of non-relaxed clusters are identified. The distribution of WAT peculiar velocities is found to be narrow and centered on zero. The X-ray images show that WAT clusters appear to have more X-ray substructure than a comparison sample of clusters. Overlays with radio and optical images reveal X-ray peaks coincident with the WATs in all cases. A strong correlation is found between the bending direction of the WAT and elongations of X-ray emission in the immediate vicinity of the WAT. Some WAT clusters appear to be undergoing a major merger, but the majority are in a subtler, unrelaxed state. The X-ray elongation correlation, combined with the small peculiar velocities has possible implications for WAT bending: (1) WATs are being bent by the motion of the gas, not the host galaxy, or (2) WATs are bent by the motion of the galaxy but a much lower velocity is required for ram pressure bending than has been theorized. The first option has the additional implication that WAT clusters are in the process of hierarchical formation.
- Pub Date:
- January 1995
- Physics: Astronomy and Astrophysics