We present a study of the nearby post-merger giant elliptical galaxy , NGC 5128 ( Centaurus A ) , in which we use the properties of its globular cluster ( GC ) and planetary nebula ( PN ) systems to constrain its evolution .
Using photometric and spectroscopic data for 215 GCs presented in Paper I , we study trends in age , metallicity , and kinematics for the GC system .
We confirm that the GC metallicity distribution is bimodal , and show that these two sub-populations have different properties .
Using spectral line index measurements of the brightest clusters , the metal-poor GCs have old ages like the Milky Way globular clusters , while the metal-rich GCs have H \beta line-strengths that could be interpreted as a mean age of \sim 5 ^ { +3 } _ { -2 } Gyr .
Both populations appear to have [ Mg/Fe ] ratios consistent with that of the Galactic GC system , although this quantity is not very well-constrained .
The kinematics of the metal-rich GCs are similar to those of the planetary nebulae , exhibiting significant rotation about a misaligned axis , while the metal-poor GCs have a higher velocity dispersion and show a weaker kinematic correlation with the field stars .
The total gravitating mass of NGC 5128 derived from the GCs is in excellent agreement with the value derived from stellar ( PN ) kinematics .
We suggest that these and other data support a picture in which the main body of NGC 5128 was formed 3–8 Gyr ago by the dissipational merger of two unequal-mass disk galaxies supplemented by the continual accretion of both gas-rich and gas-poor satellites .