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 ) .
The colour–magnitude relation ( CMR ) and the relation between luminosity and mean effective surface brightness for galaxies in the central region of Antlia have been previously studied in Paper I of the present series .
Now we confirm 22 early-type galaxies as Antlia members , using GEMINI–GMOS and MAGELLAN–MIKE spectra .
Among them , 15 are dEs from the FS90 Antlia Group catalogue , 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 M _ { B } = -10.1 ~ { } ( B _ { T } = 22.6 ) mag .
With these new data , we built an improved CMR in the Washington photometric system , i.e .
integrated T _ { 1 } magnitudes versus ( C - T _ { 1 } ) 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 .
Size and position , with respect to massive galaxies , of the dSph candidates are estimated and compared to Local Group couterparts .