J/A+A/574/A21 Isolated elliptical galaxies and GC (Richtler+, 2015)
Isolated elliptical galaxies and their globular cluster systems.
II. NGC 7796 - globular clusters, dynamics, companion.
Richtler T., Salinas R., Lane R.R., Hilker M., Schirmer M.
<Astron. Astrophys., 574, A21-21 (2015)>
=2015A&A...574A..21R 2015A&A...574A..21R
ADC_Keywords: Galaxies, nearby ; Clusters, globular
Keywords: galaxies: elliptical and lenticular, cD -
galaxies: individual: NGC 7796 - galaxies: kinematics and dynamics -
galaxies: star clusters: general - galaxies: stellar content
Abstract:
Rich globular cluster systems, particularly the metal-poor part of
them, are thought to be the visible manifestations of long-term
accretion processes. The invisible part is the dark matter halo, which
may show some correspondence to the globular cluster system. It is
therefore interesting to investigate the globular cluster systems of
isolated elliptical galaxies, which supposedly have not experienced
extended accretion. We investigate the globular cluster system of the
isolated elliptical NGC 7796, present new photometry of the galaxy,
and use published kinematical data to constrain the dark matter
content. Deep images in B and R, obtained with the VIsible MultiObject
Spectrograph (VIMOS) at the VLT, form the data base. We performed
photometry with DAOPHOT and constructed a spherical photometric model.
We present isotropic and anisotropic Jeans-models and give a
morphological description of the companion dwarf galaxy. The globular
cluster system has about 2000 members, so it is not as rich as those
of giant ellipticals in galaxy clusters with a comparable stellar
mass, but richer than many cluster systems of other isolated
ellipticals. The colour distribution of globular clusters is bimodal,
which does not necessarily mean a metallicity bimodality. The
kinematic literature data are somewhat inconclusive. The velocity
dispersion in the inner parts can be reproduced without dark matter
under isotropy. Radially anisotropic models need a low stellar
mass-to-light ratio, which would contrast with the old age of the
galaxy. A MONDian model is supported by X-ray analysis and previous
dynamical modelling, but better data are necessary for a confirmation.
The dwarf companion galaxy NGC 7796-1 exhibits tidal tails, multiple
nuclei, and very boxy isophotes. NGC 7796 is an old, massive isolated
elliptical galaxy with no indications of later major star formation
events as seen frequently in other isolated ellipticals. Its
relatively rich globular cluster system shows that isolation does not
always mean a poor cluster system. The properties of the dwarf
companion might indicate a dwarf-dwarf merger.
Description:
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* Sorry, but there are no data that should be available at CDS, *
* contrary to what announced in the paper *
* *
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(End) Patricia Vannier [CDS] 05-Mar-2015