The Next Generation Fornax Survey (NGFS). II. The Central Dwarf Galaxy Population

We present a photometric study of the dwarf galaxy population in the core region (≲r _vir/4) of the Fornax galaxy cluster based on deep u‧g‧i‧ photometry from the Next Generation Fornax Cluster Survey. All imaging data were obtained with the Dark Energy Camera mounted on the 4 m Blanco telescope at the Cerro Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities -17 ≲ M _g‧ ≲ -8 mag, corresponding to typical stellar masses of 9.5≳ {log}{{ \mathcal M }}_\star /{M}_⊙ ≳ 5.5, reaching ∼3 mag deeper in point-source luminosity and ∼4 mag deeper in surface brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that the dwarf galaxy surface-brightness profiles are well represented by single-component Sérsic models with average Sérsic indices of < n{> }_{u^\prime ,g^\prime ,i^\prime} =(0.78{--}0.83)+/- 0.02 and average effective radii of < {r}_e{> }_{u^\prime ,g^\prime ,i^\prime} =(0.67{--}0.70)+/- 0.02 {kpc}. Color-magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass-metallicity relation reveals that the average faint dwarf galaxy is likely older than ∼5 Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: (1) dwarf galaxies assemble mass inside the half-mass radius up to {log}{{ \mathcal M }}_\star ≈ 8.0, (2) isometric mass assembly occurs in the range 8.0 ≲ {log}{{ \mathcal M }}_\star /{M}_⊙ ≲ 10.5, and (3) massive galaxies assemble stellar mass predominantly in their halos at {log}{{ \mathcal M }}_\star ≈ 10.5 and above.