We report the photometric properties of 16 dwarf galaxies , 15 of which are newly identified , in the Western halo of the nearby giant elliptical galaxy NGC 5128 .
All candidates are found at projected distances \sim 100 - 225 kpc from their giant host , with luminosities -10.82 \leq M _ { V } / { mag } \leq -7.42 and effective radii 4 \arcsec \la r _ { eff } \la 17 \arcsec ( or 75 \la r _ { eff } / { pc } \la 300 at the distance of NGC 5128 ) .
We compare to other low-mass dwarf galaxies in the local universe and find them to populate the faint/compact extension of the size-luminosity relation that was previously not well-sampled by dwarf galaxies in the Centaurus A system , with optical colors similar to compact stellar systems like globular clusters and ultra-compact dwarf galaxies despite having much more diffuse morphologies .
From optical u ^ { \prime } g ^ { \prime } r ^ { \prime } i ^ { \prime } z ^ { \prime } photometry , stellar masses are estimated to be 5.17 \leq \log { \cal M } _ { \star } / M _ { \odot } \leq 6.48 , with colors that show them to fall redward of the dwarf galaxy mass-metallicity relation .
These colors suggest star formation histories that require some mechanism that would give rise to extra metal enrichment such as primordial formation within the halos of their giant galaxy hosts , non-primordial star formation from previously enriched gas , or extended periods of star formation leading to self-enrichment .
We also report the existence of at least two sub-groups of dwarf candidates , each subtending \la 15 \arcmin on the sky , corresponding to projected physical separations of 10 - 20 kpc .
True physical associations of these groups , combined with their potentially extended star formation histories , would imply that they may represent dwarf galaxy groups in the early stage of interaction upon infall into a giant elliptical galaxy halo in the very nearby universe .