A large population of ultra-compact dwarf galaxies in the Hydra I cluster

Misgeld, I.; Mieske, S.; Hilker, M.; Richtler, T.; Georgiev, Iskren Y.; Schuberth, Y.

doi:10.1051/0004-6361/201116728

Cited by 67 publications

(71 citation statements)

References 89 publications

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“…The most tjerabko@eso.org pavel@astro.uni-bonn.de massive known old UCDs have magnitudes of M V ≈ −14. The presence of UCDs has been reported also in other galaxy clusters, for example Virgo (Drinkwater et al 2004), Coma (Price et al 2009), Centaurus (Mieske et al 2007), Hydra I (Misgeld et al 2011), and Perseus (Penny et al 2012), or in massive intermediate-redshift clusters (e.g. Zhang & Bell 2017).…”

Section: Introductionmentioning

confidence: 76%

The formation of ultra compact dwarf galaxies and massive globular clusters

Jeřabková

Kroupa

Dabringhausen

et al. 2017

A&A

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The stellar initial mass function (IMF) has been described as being invariant, bottom-heavy, or top-heavy in extremely dense starburst conditions. To provide usable observable diagnostics, we calculate redshift dependent spectral energy distributions of stellar populations in extreme star-burst clusters, which are likely to have been the precursors of present day massive globular clusters (GCs) and of ultra compact dwarf galaxies (UCDs). The retention fraction of stellar remnants is taken into account to assess the mass to light ratios of the ageing star-burst. Their redshift dependent photometric properties are calculated as predictions for James Webb Space Telescope (JWST) observations. While the present day GCs and UCDs are largely degenerate concerning bottom-heavy or top-heavy IMFs, a metallicity-and density-dependent top-heavy IMF implies the most massive UCDs, at ages <100 Myr, to appear as objects with quasar-like luminosities with a 0.1-10% variability on a monthly timescale due to core collapse supernovae.

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Section: Introductionmentioning

confidence: 76%

The formation of ultra compact dwarf galaxies and massive globular clusters

Jeřabková

Kroupa

Dabringhausen

et al. 2017

A&A

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“…It is interesting to consider the occurrence of PNe with velocities smaller than 1500 km s −1 in which range two GCs are also found (1293 km s −1 and 1570 km s −1 , Misgeld et al 2011). These are deviations of partly more than 3σ for a Gaussian distribution centered on NGC 3311, corresponding to a probability of 0.1% or less.…”

Section: Comparison Of Globular Cluster Velocities With Planetary Nebmentioning

confidence: 99%

“…We merged two VIMOS programmes, using multi-slit masks with the medium resolution grism. Details of the observations, data reduction, and derivation of radial velocities are described by Misgeld et al (2011). The VLT/FORS1 images in the V-band that provide the photometric model of NGC 3311, are discussed in Misgeld et al (2008).…”

Section: Observations and Datamentioning

confidence: 99%

The dark halo of the Hydra I galaxy cluster: core, cusp, cosmological?

Richtler

Salinas

Misgeld³

et al. 2011

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Context. Some galaxy clusters exhibit shallow or even cored dark matter density profiles in their central regions rather than the predicted steep or cuspy profiles, conflicting with the standard understanding of dark matter. NGC 3311 is the central cD galaxy of the Hydra I cluster (Abell 1060). Aims. We use globular clusters around NGC 3311, combined with kinematical data of the galaxy itself, to investigate the dark matter distribution in the central region of Hydra I. Methods. Radial velocities of 118 bright globular clusters, based on VLT/VIMOS mask spectroscopy, are used to calculate velocity dispersions which are well defined out to 100 kpc. NGC 3311 is the most distant galaxy for which this kind of study has been performed. We also determine the velocity dispersions of the stellar component from long-slit spectroscopy of NGC 3311 acquired with VLT/FORS1 out to 20 kpc. We present a new photometric model for NGC 3311, based on deep VLT/FORS1 images in the V-band. We search for a dark halo that, in the context of a spherical Jeans model, can reproduce the kinematical data. We also compare the radial velocity distributions of globular clusters and planetary nebulae. Results. The projected stellar velocity dispersion rises from a central low value of about 185 km s −1 to 350 km s −1 at a radius of 20 kpc. The globular cluster dispersion rises as well from 500 km s −1 at 10 kpc to about 800 km s −1 at 100 kpc, comparable to the velocity dispersion of the cluster galaxies. A dark matter halo with a core (Burkert halo) closely reproduces the velocity dispersions of stars and globular clusters simultaneously under isotropy. The central stellar velocity dispersions predicted by cosmological NFW halos do not agree well with those observed, while the globular clusters allow a wide range of halo parameters. A suspected radial anisotropy of the stellar population found in merger simulations aggravates the disagreement with observations. A slight tangential anisotropy would enable the data to be more accurately reproduced. However, we find discrepancies with previous kinematical data that we cannot resolve, which may indicate a more complicated velocity pattern. Conclusions. Although one cannot conclusively demonstrate that the dark matter halo of NGC 3311 has a core rather than a cusp, a core seems to be most consistent with the present data. A more complete coverage of the velocity field and a more thorough analysis of the anisotropy is required to reach firm conclusions.

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“…), we focus on the kinematic properties, discuss the implications for the mass profile of NGC 3311, and explore possible formation histories of the massive star clusters observed by Misgeld et al (2011). In the current paper, we present the spatial map of the stellar population parameters, ages, and abundances out to large radii.…”

Section: Introductionmentioning

confidence: 99%

The Hydra I cluster core

Barbosa

Arnaboldi

Coccato

et al. 2016

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Context. The history of the mass assembly of brightest cluster galaxies may be studied by mapping the stellar populations at large radial distances from the galaxy centre, where the dynamical times are long and preserve the chemodynamical signatures of the accretion events. Aims. We provide extended and robust measurements of the stellar population parameters in NGC 3311, the cD galaxy at the centre of the Hydra I cluster, and out to three effective radii. We wish to characterize the processes that drove the build-up of the stellar light at all these radii. Methods. We obtained the spectra from several regions in NGC 3311 covering an area of ∼3 arcmin 2 in the wavelength range 4800 λ(Å) 5800, using the FORS2 spectrograph at the Very Large Telescope in the Mask exchange unit (MXU) mode. We measured the equivalent widths of seven absorption-features defined in the Lick/IDS system, which were modelled by single stellar populations, to provide luminosity-weighted ages, metallicities, and alpha element abundances. Results. The trends in the Lick indices and the distribution of the stellar population parameters indicate that the stars of NGC 3311 may be divided in two radial regimes, one within and the another beyond one effective radius, R e = 8.4 kpc, similar to the distinction between the inner galaxy and the external halo derived from the NGC 3311 velocity dispersion profile. The inner galaxy (R ≤ R e ) is old (age ∼14 Gyr), has negative metallicity gradients and positive alpha element gradients. The external halo is also very old, but has a negative age gradient. The metal and element abundances of the external halo both have a large scatter, indicating that stars from a variety of satellites with different masses have been accreted. The region in the extended halo associated with the off-centred envelope at 0• < PA < 90• has higher metallicity with respect to the symmetric external halo. Conclusions. The different stellar populations in the inner galaxy and extended halo reflect the dominance of in situ stars in the former and the accreted origin for the large majority of the stars in the latter. The low value of the velocity dispersion in the inner galaxy indicates that its stars are bound to the galaxy's gravitational potential, and the abundances and gradients suggest that the inner galaxy is formed in an outside-in scenario of merging gas-rich lumps, reminiscent of the first phase of galaxy formation. The external halo has a higher velocity dispersion, it is dynamically hotter than the galaxy and its stars are gravitationally driven by the cluster's gravitational potential. The stars in the external halo were removed from their parent galaxies, either disks with truncated star formation, or the outer regions of early-type galaxies. Late mass accretion at large radii is now coming from the tidal stripping of stars from dwarfs and S0 galaxies. These results provide supporting evidence for the recent theoretical models of formation of massive ellipticals as a two-phase process.

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A large population of ultra-compact dwarf galaxies in the Hydra I cluster

Cited by 67 publications

References 89 publications

The formation of ultra compact dwarf galaxies and massive globular clusters

The formation of ultra compact dwarf galaxies and massive globular clusters

The dark halo of the Hydra I galaxy cluster: core, cusp, cosmological?

The Hydra I cluster core

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