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 ($< r_m vir/4$) 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 $9.5gtrsim logcal M_star/M_odot gtrsim 5.5$, 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 S'ersic models with average S'ersic indices of $langle n angle_u',g',i'=(0.78-0.83) pm 0.02$, and average effective radii of $langle r_e angle_u',g',i'!=(0.67-0.70) pm 0.02$ 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 $logcal M_star$ ~8.0, ii) isometric mass assembly in the range $8.0 < logcal M_star/M_odot < 10.5$, and iii) massive galaxies assemble stellar mass predominantly in their halos at $logcal M_star$ ~10.5 and above