A new Compact Elliptical galaxy in the Antlia cluster confirmed through GEMINI-GMOS spectroscopy

SMITH CASTELLI, A. V.; FAIFER, F.; BASSINO, L. P.; RICHTLER, T.; CELLONE, S. A.

Bonn

Workshop; Tidal Dwarf Galaxies: Ghosts from structure formation; 2009

Argelander-Institut für Astronomie

Compact elliptical (cE) galaxies are low luminosity systems that display notorious high surface brightness in comparison with ellipticals of the same luminosity (Nieto & Prugniel 1987) and correspondingly small sizes (Choi et al. 2002; Graham 2002). They constitute a very rare group, as only five objects have been confirmed as such, in addition to the prototype M32 (see Graham 2002 for an alternative interpretation). The known examples are all companions of larger galaxies. They are M32 itself, a satellite of the M31 (Andromeda) spiral galaxy, NGC 4486B close to M87 in the Virgo cluster (Sandage & Binggeli 1984; Davidge 1991), NGC 5846A close to the giant elliptical NGC 5846 (Davidge 1991; Mahdavi, Trentham & Tully 2005), A496cE close to the cluster dominant (cD) galaxy of the cluster Abell 496 (Chilingarian et al. 2007), and two objects in the Abell 1689 cluster (CGA1689,1 and CGA1689,2;Mieske et al. 2005). Some effort has been made to find more examples of these very rare objects in nearby clusters or groups, such as Fornax (Drinkwater et al. 2001) and Leo (Ziegler & Bender 1998). However, all the examined candidates have been rejected as cE galaxies. As the questions related to their origin and role in the framework of galaxy evolution remain still open, it would be of great interest to find more objects and study them in relation to their environment.In this contribution we report the discovery of a new cE galaxyin the Antlia cluster. From GEMINI-GMOS spectra, we have calculated an heliocentric radial velocity of 2900 km s-1,confirming its membership to Antlia. This is the seventh cE galaxy confirmed up to now. It has a projected diameter size of 4.8 kpc, <mu_eff>=18.4 mag arcsec-2 (R band), MR=-17.2 mag, and it is located at a projected distance of ~8 kpc from NGC 3258, a giant elliptical galaxy. It is the only cE showing clear evidence of interaction with its bright companion. Thespectrum of this galaxy displays very similar features to that of the halo of NGC 3258, which reinforces the classification of FS90 110 as a cE galaxy. Our future work will be aimed to analyse the spectrum of this galaxy in comparison with those of other confirmed cE galaxies, ?normal? dwarf ellipticals and the halo of NGC 3258.