A Puzzling Merger in A3266: The Hydrodynamic Picture from XMM-Newton

Using a mosaic of nine XMM-Newton observations, we study the hydrodynamic state of the merging cluster of galaxies Abell 3266. The high signal-to-noise ratio of spectroscopic data of XMM-Newton allows us to determine the thermodynamic conditions of the intracluster medium on ~50 kpc scales. High statistical quality X-ray data reveal the presence of an extended region of low-entropy gas (LEG) running northeast from the primary cluster core along the nominal merger axis. The LEG is a major feature distinguishing the merger event in A3266 from other clusters. The mass of the low-entropy gas is ~1.3×10¹³ M_solar. We test the possibility that the origin of the observed low-entropy gas is related either to the disruption of a preexisting cooling core in Abell 3266 or to the stripping of gas from an infalling subcluster. We find that the low-entropy gas has a metallicity 1.5-2 times higher than the bulk of the cluster, yet lower than one-half the solar value typical for the cool cores. In addition, both the radial pressure and entropy profiles, as well as the iron abundance of Abell 3266, do not resemble those in other known cool core clusters (e.g., Abell 478). Thus, we conclude that our observations favor a scenario in which the low-entropy region corresponds to subcluster gas stripped from its dark matter halo. In this scenario the subcluster would be falling onto the core of A3266 from the foreground, having a velocity component in the observer plane toward the southwest. The arguments based on both velocity dispersion and gas mass measurements suggest a mass ratio in the merger of 1:10.