Galaxy populations in the Antlia cluster - III. Properties of faint
  early-type galaxies
  (Abridge) We present a new analysis of the early-type galaxy population in
the central region of the Antlia cluster, focusing on the faint systems like
dwarf ellipticals (dE) and dwarf spheroidals (dSph). We confirm 22 early-type
galaxies as Antlia members, using GEMINI-GMOS and MAGELLAN-MIKE spectra. Among
them, 2 belong to the rare type of compact ellipticals (cE), and 5 are new
faint dwarfs that had never been catalogued before. In addition, we present 16
newly identified low surface brightness galaxy candidates, almost half of them
displaying morphologies consistent with being Antlia's counterparts of Local
Group dSphs, that extend the faint luminosity limit of our study down to MB =
-10.1 (BT = 22.6) mag. We built an improved CMR in the Washington photometric
system, i.e. integrated T1 magnitudes versus (C - T1) colours, which extends
\sim 4 mag faintwards the limit of spectroscopically confirmed Antlia members.
When only confirmed early-type members are considered, this relation extends
over 10 mag in luminosity with no apparent change in slope or increase in
colour dispersion towards its faint end. The intrinsic colour scatter of the
relation is compared with those reported for other clusters of galaxies; we
argue that it is likely that the large scatter of the CMR, usually reported at
faint magnitudes, is mostly due to photometric errors along with an improper
membership/morphological classification. The distinct behaviour of the
luminosity versus mean effective surface brightness relation at the bright and
faint ends is analyzed, while it is confirmed that dE galaxies on the same
relation present a very similar effective radius, regardless of their colour.
The projected spatial distribution of the member sample confirms the existence
of two groups in Antlia, each one dominated by a giant elliptical galaxy and
with one cE located close to each giant.
