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 (\(< r_{\rm vir}/4\)) 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-meter 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 \(9.5\gtrsim \log{\cal M}_{\star}/M_\odot \gtrsim 5.5\), reaching \(\sim\!3\) mag deeper in point-source luminosity and \(\sim\!4\) mag deeper in surface-brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that surface-brightness profiles are well represented by single-component Sérsic models with average Sérsic indices of \(\langle n\rangle_{u',g',i'}=(0.78-0.83) \pm 0.02\), and average effective radii of \(\langle r_e\rangle_{u',g',i'}\!=(0.67-0.70) \pm 0.02\) 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: i) dwarf galaxies assemble mass inside the half-mass radius up to \(\log{\cal M}_{\star}\) ~8.0, ii) isometric mass assembly in the range \(8.0 < \log{\cal M}_{\star}/M_\odot < 10.5\), and iii) massive galaxies assemble stellar mass predominantly in their halos at \(\log{\cal M}_{\star}\) ~10.5 and above.