We present the analysis of 61 nucleated dwarf galaxies in the central regions ( \la R _ { vir } / 4 ) of the Fornax galaxy cluster .
The galaxies and their nuclei are studied as part of the Next Generation Fornax Survey ( NGFS ) using optical imaging obtained with the Dark Energy Camera ( DECam ) mounted at Blanco/CTIO and near-infrared data obtained with VIRCam at VISTA/ESO .
We decompose the nucleated dwarfs in nucleus and spheroid , after subtracting the surface brightness profile of the spheroid component and studying the nucleus using PSF photometry .
In general , nuclei are consistent with colors of confirmed metal-poor globular clusters , but with significantly smaller dispersion than other confirmed compact stellar systems in Fornax .
We find a bimodal nucleus mass distribution with peaks located at \log ( { \cal M _ { * } } / M _ { \odot } ) \simeq 5.4 and \sim 6.3 .
These two nucleus sub-populations have different stellar population properties , the more massive nuclei are older than \sim 2 Gyr and have metal-poor stellar populations ( Z \leq 0.02 Z _ { \odot } ) , while the less massive nuclei are younger than \sim 2 Gyr with metallicities in the range 0.02 < Z / Z _ { \odot } \leq 1 .
We find that the nucleus mass ( { \cal M } _ { nuc } ) vs. galaxy mass ( { \cal M } _ { gal } ) relation becomes shallower for less massive galaxies starting around 10 ^ { 8 } M _ { \odot } and the mass ratio \eta _ { n } = { \cal M } _ { nuc } / { \cal M } _ { gal } shows a clear anti-correlation with { \cal M } _ { gal } for the lowest masses , reaching 10 \% .
We test current theoretical models of nuclear cluster formation and find that they can not fully reproduce the observed trends .
A likely mixture of in-situ star formation and star-cluster mergers seem to be acting during nucleus growth over cosmic time .