The centaurus group and the outer halo of NGC 5128: Are they dynamically connected?

NGC 5128, a giant elliptical galaxy only similar to 4 Mpc away, is the dominant member of a galaxy group of over 80 probable members. The Centaurus group provides an excellent sample for a kinematic comparison between the halo of NGC 5128 and its surrounding satellite galaxies. A new study, presented here, shows no kinematic difference in rotation amplitude, rotation axis, or velocity dispersion between the halo of NGC 5128, determined from over similar to 340 of its globular clusters, and those of the Centaurus group as a whole. These results suggest NGC 5128 could be behaving in part as the inner component to the galaxy group, and could have begun as a large initial seed galaxy, gradually built up by minor mergers and satellite accretions, consistent with simple cold dark matter models. The masses and mass-to-light ratios in the B band, corrected for projection effects, are determined to be (1.3 +/- 0.5); 10(12) M-circle dot and 52 +/- 22 M-circle dot L-circle dot(-1) for NGC 5128 out to a galactocentric radius of 45 kpc and ( 9.2 +/- 3.0); 10(12) M-circle dot and 153 +/- 50 M-circle dot L-circle dot(-1) for the Centaurus group, consistent with previous studies.