The mass of the Centaurus A group of galaxies

The mass M and the radius R-h of the Centaurus A group are estimated from t he positions and radial velocities of 30 probable cluster members. For an a ssumed distance of 3.9 Mpc, it is found that R-h similar to 640 kpc. The ve locity dispersion in the Cen A group is 114 +/- 21 km s(-1). From this valu e and R-h = 640 kpc, the virial theorem yields a total mass of 1.4 x 10(13) M. for the Cen A group. The projected mass method gives a mass of 1.8 x 10 (13) M.. These values suggest that the Cen A group is about 7 times as mass ive as the Local Group. The Cen A mass-to-light ratio is found to be M/L-B = 155-200 (M/L).. The cluster has a zero-velocity radius R-0 = 2.3 Mpc.