Open questions in the Antlia cluster

SMITH CASTELLI, ANALIA; BASSINO, LILIA; RICHTLER, TOM; FAIFER, FAVIO; CELLONE, SERGIO

Potsdam, Alemania

Workshop; Open Problems in Galaxy Formation; 2009

We present the results of a study of the galaxy population of the central region of the Antlia cluster. The investigated sample includes 100 galaxies from the FS90 Antlia Group catalogue and 44 newly identified galaxies. These results are part of the first author´s PhD Thesis, defended last December at La Plata National University (Argentina).Antlia is the third nearest well-populated galaxy cluster after Virgo and Fornax. Despite its proximity, richness and concentration, it was practically unexplored until we began our Antlia Cluster Project (Smith Castelli et al. 2008a,b). We have studied the early-type galaxies, from giants to dwarfs, and the photometric relations they define. With that aim, we used CCD images obtained with MOSAIC-CTIO and FORS1-VLT. The membership statusof bright galaxies and a sample of faint ones has been established by means of spectra from IMACS-MAGELLAN and GMOS-GEMINI.The first colour-magnitude relation (CMR) of early-type galaxies in Antlia has been built. Confirmed cluster members and new dwarf galaxy candidates follow a well-defined CMR. Such CMR extends 11 magnitudes with no apparent change of slope or increase in thescatter towards faint luminosities. This slope is in agreement with those displayed by other clusters like Virgo, Fornax, Perseus and Coma. What would that mean?As reported in the literature, a considerable increment in the colour scatter is present in other CMRs towards the faint end. Has it a physical origin or can be accounted by photometric errors and/or background contamination?Galaxies involved in the Antlia CMR also follow a luminosity-metallicity relation, which is extended towards fainter magnitudes by Local Group dwarf galaxies. The metallicities of the Antlia galaxies were estimated by means of a colour-metallicity relation valid for globular clusters. Then, how can this match be interpreted?