The early-type dwarf galaxy population of the Fornax cluster

Free access article

Issue		A&A Volume 463, Number 2, February IV 2007


Page(s)		503 - 512
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20066300

A&A 463, 503-512 (2007)
DOI: 10.1051/0004-6361:20066300

The early-type dwarf galaxy population of the Fornax cluster

S. Mieske¹, M. Hilker², L. Infante³, and C. Mendes de Oliveira⁴

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
    e-mail: smieske@eso.org
² Argelander Institut für Astronomie, Abteilung Sternwarte, Auf dem Hügel 71, 53121 Bonn, Germany
    e-mail: mhilker@astro.uni-bonn.de
³ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
    e-mail: linfante@astro.puc.cl
⁴ Instituto de Astronomia, Geofísica, e Ciências Atmosféricas, Departamento de Astronomia, Universidade de São Paulo, Rua do Matáo 1226, Cidade Universitãria, 05508-900 São Paulo, SP, Brazil
    e-mail: oliveira@astro.iag.usp.br

(Received 25 August 2006 / Accepted 17 October 2006 )

Abstract
Aims.We analyse the photometric properties of the early-type Fornax cluster dwarf-galaxy population ( $M_{\rm V}>-17$ mag), based on a wide-field imaging study of the central cluster area in V and I bandpasses. We used the instrument/telescope combination IMACS/Magellan at Las Campanas Observatory, providing much larger light-collecting area and better image resolution than previous wide-field imaging surveys.
Methods.We created a fiducial sample of Fornax cluster dwarf ellipticals (dEs) in the following three steps. (1) To verify cluster membership, we measured I-band surface brightness fluctuations (SBF) distances to candidate dEs known from previous surveys. (2) We re-assessed morphological classifications for those candidate dEs that are too faint for SBF detection. (3) We searched for new candidate dEs in the size-luminosity regime close to the resolution limit of previous surveys.
Results.(1) We confirm cluster membership for 28 candidate dEs in the range $-16.6<M_{\rm V}<-10.1$ mag by means of SBF measurement. We find no SBF background galaxy. (2) Of 51 other candidate dEs in the range $-13.2<M_{\rm V}<-8.6$ mag, 2/3 are confirmed as probable cluster members by morphological re-assessment, while 1/3 are re-classified as probable background objects. (3) We find 12 new dE candidates in the range $-12.3<M_{\rm V}<-8.8$ mag, two of which are directly confirmed via SBF measurement. The resulting fiducial dE sample follows a well-defined surface brightness-magnitude relation, showing that Fornax dEs are about 40% larger than Local Group dEs. The sample also defines a colour-magnitude relation that appears slightly shallower than that of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax has a very flat faint end slope $\alpha \simeq -1.1 \pm 0.1$ . We discuss these findings in the context of structure-formation theories.
Conclusions.The SBF method is a very powerful tool to help constrain the faint end of the galaxy luminosity function in nearby galaxy clusters. For the Fornax cluster, morphological cluster memberships - if performed at sufficient resolution - are very reliable.

Key words: galaxies: clusters: individual: Fornax cluster -- galaxies: dwarf -- galaxies: fundamental parameters -- galaxies: luminosity function, mass function -- techniques: photometric

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