Issue |
A&A
Volume 472, Number 1, September II 2007
|
|
---|---|---|
Page(s) | 111 - 119 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20077631 | |
Published online | 26 June 2007 |
A search for ultra-compact dwarf galaxies in the Centaurus galaxy cluster *,**
1
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: [ smieske; mhilker; ajordan; mkissler] @eso.org
2
Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile e-mail: linfante@astro.puc.cl
Received:
11
April
2007
Accepted:
14
June
2007
Aims.Our aim is to extend the investigations of ultra-compact dwarf galaxies (UCD) beyond the well studied Fornax and Virgo clusters.
Methods.We measured spectroscopic redshifts of about 400 compact object candidates with 19.2 < V < 22.4 mag in the central region of the Centaurus galaxy cluster (d = 43 Mpc), using 3 pointings with VIMOS@VLT. The luminosity range of the candidates covers the bright end of the globular cluster (GC) luminosity function and the luminosity regime of UCDs in Fornax and Virgo. Within the area surveyed, our completeness in terms of slit allocation is ≈30%.
Results.We find 27 compact objects with radial velocities consistent with
them being members of Centaurus, covering an absolute magnitude
range -12.2 < MV < -10.9 mag. We do not find counterparts to the
two very large and bright UCDs in Fornax and Virgo with
MV = -13.5 mag, possibly due to survey incompleteness. The
compact objects' distribution in magnitude and space is
consistent with that of the GC population. Their kinematics and
spatial distribution indicate that they are associated more to
the central galaxies than to the overall cluster potential. The
compact objects have a mean metallicity consistent with that of
the metal-rich globular cluster sub-population. Compact objects
with high spectra exhibit solar [ α/Fe] abundances,
consistent with typical dwarf elliptical galaxy values and unlike
galactic bulge globular clusters. HST based size estimates for a
sub-sample of eight compact objects reveal the existence of one
very large object with half-light radius rh around 30 pc,
having MV = -11.6 mag (
107
). This source
shows super-solar [ α/Fe] abundances. Seven further
sources are only marginally larger than typical GCs with rh in
the range 4 to 10 pc. Those sources exhibit a large scatter in
[ α/Fe] abundances.
Conclusions.We consider the largest compact object found to be the only bona fide UCD detected in our study. In order to improve our understanding of UCDs in Centaurus, a significant increase of our survey completeness is necessary.
Key words: galaxies: clusters: individual: Centaurus / galaxies: dwarf / galaxies: fundamental parameters / galaxies: nuclei / galaxies: star clusters
© ESO, 2007
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