We present a comprehensive high spatial-resolution imaging study of globular clusters ( GCs ) in NGC 1399 , the central giant elliptical cD galaxy in the Fornax galaxy cluster , conducted with the Advanced Camera for Surveys ( ACS ) aboard the Hubble Space Telescope ( HST ) .
Using a novel technique to construct drizzled PSF libraries for HST/ACS data , we accurately determine the fidelity of GC structural parameter measurements from detailed artificial star cluster experiments and show the superior robustness of the GC half-light radius , r _ { h } , compared with other GC structural parameters , such as King core and tidal radius .
The measurement of r _ { h } for the major fraction of the NGC 1399 GC system reveals a trend of increasing r _ { h } versus galactocentric distance , R _ { gal } , out to about 10 kpc and a flat relation beyond .
This trend is very similar for blue and red GCs which are found to have a mean size ratio of r _ { h,red } / r _ { h,blue } = 0.82 \pm 0.11 at all galactocentric radii from the core regions of the galaxy out to \sim 40 kpc .
This suggests that the size difference between blue and red GCs is due to internal mechanisms related to the evolution of their constituent stellar populations .
Modeling the mass density profile of NGC 1399 shows that additional external dynamical mechanisms are required to limit the GC size in the galaxy halo regions to r _ { h } \approx 2 pc .
We suggest that this may be realized by an exotic GC orbit distribution function , an extended dark matter halo , and/or tidal stress induced by the increased stochasticity in the dwarf halo substructure at larger galactocentric distances .
We compare our results with the GC r _ { h } distribution functions in various galaxies and find that the fraction of extended GCs with r _ { h } \geq 5 pc is systematically larger in late-type galaxies compared with GC systems in early-type galaxies .
This is likely due to the dynamically more violent evolution of early-type galaxies .
We match our GC r _ { h } measurements with radial velocity data from the literature and split the resulting sample at the median r _ { h } value into compact and extended GCs .
We find that compact GCs show a significantly smaller line-of-sight velocity dispersion , \langle \sigma _ { cmp } \rangle = 225 \pm 25 km s ^ { -1 } , than their extended counterparts , \langle \sigma _ { ext } \rangle = 317 \pm 21 km s ^ { -1 } .
Considering the weaker statistical correlation in the GC r _ { h } -color and the GC r _ { h } - R _ { gal } relations , the more significant GC size-dynamics relation appears to be astrophysically more relevant and hints at the dominant influence of the GC orbit distribution function on the evolution of GC structural parameters .