The Centaurus cluster of galaxies - II. The bimodal velocity structure

Abstract

The bimodal velocity distribution of the galaxies in the Centaurus cluster (⁠|$\alpha=12^\text h47^\text m,\enspace \delta=-41^\circ$|⁠) is discussed. The mean heliocentric velocities and line-of-sight dispersions of the two main cluster components, within 3○ of the cluster centre, are 3041, |$586\enspace\text {km}\enspace \text s^{-1}$| (denoted Cen 30) and 4570, |$262\enspace\text {km}\enspace \text s^{-1}$| (denoted Cen 45) respectively. Cen 30 is dominant, having about 2.5×the population of Cen 45. Each of the two major components has a large elliptical galaxy lying at its dynamical centre; NGC 4696 in Cen 30 and NGC 4709 in Cen 45.