We report on multi-object spectroscopy in the red spectral region of 37 candidate star clusters in an \sim 8 \times 8 arcmin ^ { 2 } field centered on the giant early-type radio galaxy NGC 1316 ( Fornax A ) , the brightest galaxy in the Fornax cluster .
Out of this sample , 24 targets are found to be genuine star clusters associated with NGC 1316 , and 13 targets are Galactic foreground stars .
For the star cluster sample , we measure a mean heliocentric velocity v _ { hel } = 1698 \pm 46 km s ^ { -1 } and a velocity dispersion \sigma = 227 \pm 33 km s ^ { -1 } within a galactocentric radius of 24 kpc .
Partly responsible for the velocity dispersion is a significant rotation in the star cluster system , with a mean velocity of \sim 175 \pm 70 km s ^ { -1 } along a position angle of \sim 6 \hbox { $ { } ^ { \circ } $ } \pm 18 \hbox { $ { } ^ { \circ } $ } .
Using the projected mass estimator and assuming isotropic orbits , the estimated total mass is ( 6.6 \pm 1.7 ) \times 10 ^ { 11 } M _ { \odot } within a radius of 24 kpc .
The mass is uncertain by about a factor of two , depending on the orbital assumptions .
The implied \cal { M } / L _ { B } ratio is in the range 3 – 6 .
Four star clusters in our sample are exceptionally luminous ( M _ { V } < -12.3 ) .
This means that ( 1 ) at least this many clusters in NGC 1316 are up to an order of magnitude more luminous than the most luminous star cluster in our Galaxy or M 31 , and ( 2 ) that the S/N ratio of their spectra allows us to measure line strengths with good accuracy .
By comparing the measured colours and equivalent widths of H \alpha and the Ca ii triplet ( \lambda \lambda 8498 , 8542 , 8662 Å ) absorption lines for those bright star clusters in our sample with those of single-burst population models ( the Bruzual & Charlot 1996 models ) , we find that they are coeval with an age of 3.0 \pm 0.5 Gyr .
Their metallicities are found to be solar to within \pm 0.15 dex .
We discuss the properties of the main body of NGC 1316 and conclude they are consistent with having hosted a major merger 3 Gyr ago as well .
The presence of intermediate-age globular clusters in NGC 1316 shows once again that globular clusters with near-solar metallicity do form during galactic mergers , and , moreover , that they can survive disruption processes taking place during the merger ( e.g. , dynamical friction , tidal disruption ) , as well as evaporation .
In this respect , NGC 1316 provides a hitherto “ missing ” evolutionary link between young merger remnants of age \sim 0.5 Gyr such as NGC 3597 , NGC 3921 and NGC 7252 on one side , and older giant ellipticals featuring bimodal colour distributions on the other side .