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Globular Cluster Systems in Nearby Dwarf Galaxies: I. HST/ACS Observations and Dynamical Properties of Globular Clusters at Low Environmental Density
Iskren Y. Georgiev, Thomas H. Puzia, Michael Hilker +1
We investigate the old globular cluster (GC) population of 68 faint (Mv>-16 mag) dwarf galaxies located in the halo regions of nearby (<12 Mpc) loose galaxy groups and in the field…
High M/L ratios of UCDs: a variation of the IMF?
S. Mieske, J. Dabringhausen, P. Kroupa +2
Various studies have established that the dynamical M/L ratios of ultra-compact dwarf galaxies (UCDs) tend to be at the limit or beyond the range explicable by standard stellar pop…
Compact stellar systems in the Fornax cluster: a UV perspective
Steffen Mieske, Michael Hilker, Dominik J. Bomans +4
In recent years, increasing evidence for chemical complexity and multiple stellar populations in massive globular clusters (GCs) has emerged, including extreme horizontal branches…
The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database
Steffen Mieske, Michael Hilker, Andres Jordan +9
We have obtained high-resolution spectra of 23 ultra-compact dwarf galaxies (UCDs) in the Fornax cluster with -10.4>M_V>-13.5 mag (10^6<M/M_*<10^8), using FLAMES/Giraffe at the VLT…
The early-type dwarf galaxy population of the Hydra I cluster
I. Misgeld, S. Mieske, M. Hilker
We analyse the properties of the early-type dwarf galaxy population in the Hydra I cluster. We investigate the galaxy luminosity function (LF), the colour-magnitude relation (CMR),…
Comparing CN and CH Line Strengths in a Homogeneous Spectroscopic Sample of 8 Galactic Globular Clusters
Andrea Kayser, Michael Hilker, Eva K. Grebel +1
Our work focuses on the understanding of the origin of CNO-anomalies, which have been detected in several Galactic globular clusters (GCs). This study is based on a homogeneous dat…
Structural Properties of Ultra-Compact Dwarf Galaxies in the Fornax and Virgo Clusters
E. A. Evstigneeva, M. J. Drinkwater, C. Y. Peng +6
We present a detailed analysis of two-band HST/ACS imaging of 21 ultra-compact dwarf (UCD) galaxies in the Virgo and Fornax Clusters. The aim of this work is to test two formation…
Old globular clusters in magellanic-type dwarf irregular galaxies
Iskren Y. Georgiev, Paul Goudfrooij, Thomas H. Puzia +1
We present a study of the old globular clusters (GC) using archival F606W and F814W HST/ACS images of 19 Magellanic-type dwarf Irregular (dIrr) galaxies found in nearby (2 - 8 Mpc)…
From star clusters to dwarf galaxies: The properties of dynamically hot stellar systems
J. Dabringhausen, M. Hilker, P. Kroupa
(Abridged) Objects with radii of 10 to 100 pc and masses in the range from 10^6 to 10^8 M_sun have been discovered during the past decade. These so-called ultra compact dwarf galax…
The dark matter halo of NGC 1399 - CDM or MOND?
T. Richtler, Y. Schuberth, M. Hilker +3
Central galaxies in galaxy clusters may be key discriminants in the competition between the cold dark matter (CDM) paradigm and modified Newtonian dynamics (MOND). We investigate t…
Stroemgren metallicity calibration: the m1, b-y relation
A. Calamida, G. Bono, P. B. Stetson +15
We performed a new calibration of the Stroemgren metallicity index m1 based on the b-y color of cluster red giant stars. The current Metallicity-Index-Color relation is not linear…
A flat faint end of the Fornax cluster galaxy luminosity function
Steffen Mieske, Michael Hilker, Leopoldo Infante +1
We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population (M_V>-17 mag), based on a wide field imaging study of the central cluster area in V a…
Stroemgren photometry of Galactic Globular Clusters. I. New Calibrations of the metallicity index
A. Calamida, G. Bono, P. B. Stetson +15
We present a new calibration of the Stroemgren metallicity index m1 using red giant (RG) stars in 4 globular clusters (GCs:M92,M13,NGC1851,47Tuc) with metallicity ranging from [Fe/…
A search for ultra-compact dwarf galaxies in the Centaurus galaxy cluster
S. Mieske, M. Hilker, A. Jordan +2
Aim: To extend the investigations of ultra-compact dwarf galaxies (UCDs) beyond the well studied Fornax and Virgo clusters. Methods: We measured spectroscopic redshifts of about 40…
Metallicity distribution of Omega Cen Red Giants based on the Stroemgren m1 metallicity index
A. Calamida, G. Bono, L. M. Freyhammer +6
We adopted uvby Stroemgren photometry to investigate the metallicity distribution of Omega Cen Red Giant (RG) stars. We provided a new empirical calibration of the Stroemgren m1 =…
Dynamical masses of ultra-compact dwarf galaxies in Fornax
M. Hilker, H. Baumgardt, L. Infante +3
Aims. We determine masses and mass-to-light ratios of five ultra-compact dwarf galaxies and one dwarf elliptical nucleus in the Fornax cluster from high resolution spectroscopy. Me…
Internal Properties of Ultra-Compact Dwarf Galaxies in the Virgo Cluster
E. A. Evstigneeva, M. D. Gregg, M. J. Drinkwater +1
We present new imaging and spectroscopic observations of six ultra-compact dwarf (UCD) galaxies in the Virgo Cluster, along with re-analysed data for five Fornax Cluster UCDs. Thes…
Medium resolution spectroscopy in Omega Centauri: abundances of 400 subgiant and turn-off region
Andrea Kayser, Michael Hilker, Tom Richtler +1
Medium resolution spectra of more than 400 subgiant and turn-off region stars in Omega Centauri were analysed. The observations were performed at the VLT/Paranal with FORS2/MXU. In…
The early-type dwarf galaxy population of the Fornax cluster
S. Mieske, M. Hilker, L. Infante +1
AIMS: We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population, based on a wide field imaging study of the central cluster area in V and I. We…
Ultra-Compact Stellar Systems in the Fornax Galaxy Cluster
P. Firth, M. J. Drinkwater, E. A. Evstigneeva +6
Our VLT (FLAMES) observations near NGC1399 investigate the connection between ultra-compact dwarf galaxies (UCDs), NGC1399 globular clusters and intra-cluster globulars. We have un…
An I-band calibration of the SBF method at blue colours
S. Mieske, M. Hilker, L. Infante
The surface brightness fluctuation (SBF) method is a powerful tool to derive distances to galaxies for which single stars cannot be resolved. Up to now, the method has been calibra…
Multi-colour Imaging of Ultra-compact Objects in the Fornax Cluster
A. M. Karick, M. D. Gregg, M. J. Drinkwater +2
Ultra-compact dwarf galaxies (UCDs) are a new type of galaxy we have discovered in the central region of the Fornax and Virgo clusters. Unresolved in ground-based imaging, UCDs hav…
UCDs - a mixed bag of objects
Michael Hilker
The name "Ultra-Compact Dwarf Galaxy" (UCD) was invented for a new type of astronomical object that has been discovered in cores of nearby galaxy clusters a decade ago. UCDs resemb…
Dynamics of the NGC 4636 Globular Cluster System - An extremely dark matter dominated galaxy?
Y. Schuberth, T. Richtler, B. Dirsch +4
We present the first dynamical study of the globular cluster system of NGC 4636. This giant elliptical galaxy is claimed to be extremely dark matter dominated, according to X-ray o…