87 research outputs found
The Surface Brightness and Colour-Magnitude Relations for Fornax Cluster Galaxies
We present BVI photometry of 190 galaxies in the central region of the Fornax
Cluster observed with the Michigan Curtis Schmidt Telescope. The cluster
members exhibit a strong surface brightness-magnitude relation in our data:
both giant and dwarf ellipticals decrease in surface brightness as luminosity
decreases. However the surface brightness-magnitude relation is no longer a
reliable method for determining cluster membership at surface brightnesses
fainter than 22 mag/sq.arcsec. The newly discovered ultra-compact dwarf
galaxies (UCDs) lie well off the normal surface brightness-magnitude relation.
We present the colour-magnitude relation for a sample of 113 cluster galaxies
as a function of morphological type. The UCDs also lie off the locus of this
relation. Their mean V-I colours are redder than dwarf galaxies of similar
luminosity, but similar to those of globular clusters associated with NGC 1399.
The location of the UCDs on both surface brightness and colour-magnitude plots
supports the hypothesis that they are the remnants of tidally stripped
nucleated dwarf elliptical galaxies.Comment: 14 pages, 8 figures. accepted for publication to MNRAS,
low-resolution version of some images, changes made in response to referee's
repor
Galaxy Disruption Caught in the Act
Direct evidence of stellar material from galaxy disruption in the
intra-cluster medium (ICM) relies on challenging observations of individual
stars, planetary nebulae and diffuse optical light. Here we show that the
ultra-compact dwarf galaxies (UCDs) we have discovered in the Fornax Cluster
are a new and easy-to-measure probe of disruption in the ICM. We present
spectroscopic observations supporting the hypothesis that the UCDs are the
remnant nuclei of tidally ``threshed'' dwarf galaxies. Deep optical imaging of
the cluster has revealed a 43-kpc long arc of tidal debris, flanking a
nucleated dwarf elliptical (dE,N) cluster member. We may be witnessing galaxy
threshing in action.Comment: 2 pages, 2 figures, to be published in "IAU Symposium 217, Recycling
Intergalactic and Interstellar Matter", ASP Conf. Serie
Compact Stellar Systems around NGC 1399
We have obtained spectroscopic redshifts of colour-selected point sources in
four wide area VLT-FLAMES fields around the Fornax Cluster giant elliptical
galaxy NGC 1399, identifying as cluster members 30 previously unknown faint
(-10.5<M_g'<-8.8) compact stellar systems (CSS), and improving redshift
accuracy for 23 previously catalogued CSS.
By amalgamating our results with CSS from previous 2dF observations and
excluding CSS dynamically associated with prominent (non-dwarf) galaxies
surrounding NGC 1399, we have isolated 80 `unbound' systems that are either
part of NGC 1399's globular cluster (GC) system or intracluster GCs. For these
unbound systems, we find (i) they are mostly located off the main stellar locus
in colour-colour space; (ii) their projected distribution about NGC 1399 is
anisotropic, following the Fornax Cluster galaxy distribution, and there is
weak evidence for group rotation about NGC 1399; (iii) their
completeness-adjusted radial surface density profile has a slope similar to
that of NGC 1399's inner GC system; (iv) their mean heliocentric recessional
velocity is between that of NGC 1399's inner GCs and that of the surrounding
dwarf galaxies, but their velocity dispersion is significantly lower; (v)
bright CSS (M_V<-11) are slightly redder than the fainter systems, suggesting
they have higher metallicity; (vi) CSS show no significant trend in
colour index with radial distance from NGC 1399.Comment: 13 pages (including supplementary table), 13 figures, 5 tables.
Accepted for publication in MNRA
A large population of ultra-compact dwarfs and bright intracluster globulars in the Fornax cluster
All the previously cataloged ultracompact dwarf (UCD) galaxies in the Fornax and Virgo clusters have 17.5 < b(J) < 20. Using the 2dF spectrograph on the Anglo-Australian Telescope, we have carried out a search for fainter UCDs in the Fornax Cluster. In the magnitude interval 19.5 < b(J) < 21.5, we have found 54 additional compact cluster members within a projected radius of 0 degrees.9 (320 kpc) of the cluster center, all of which meet our selection and observational criteria to be UCDs. These newly identified objects, however, overlap in luminosity and spatial distribution with objects classified as globular clusters (GCs) belonging to the central cluster galaxy NGC 1399; in fact, about half of the objects in our sample are included in recent catalogs of NGC 1399/Fornax GCs. The numbers, luminosity function, and spatial distributions of our compact object sample are consistent with being the bright tail of the Fornax cluster-wide GC population. Yet, our present larger sample of intergalactic compact objects forms a dynamically distinct population from both the NGC1399 GCs and the nucleated dwarf ellipticals in Fornax. This supports the interpretation that the UCDs, which populate the bright tail of the GC luminosity function, are, in some respects, a separate class of objects, at least to the extent that they have experienced a distinct dynamical history and origin, which differs from the bulk of the NGC1399 GCs. Correcting for our spectroscopic incompleteness, we estimate that there are similar to 105 +/- 13 of these brighter compact cluster objects down to b(J) < 21.5 in the central region of the Fornax, and hence these UCDs/globulars outnumber other galaxy types in this space. The differences in their dynamics and distribution compared to dwarf ellipticals (dEs) may be consistent with a threshing or tidal destruction origin, if they have come from a subpopulation of dE galaxies on initial orbits that rendered them susceptible to such processes
SDSSJ150634.27+013331.6: the second compact elliptical galaxy in the NGC5846 group
We report the discovery of the second compact elliptical (cE) galaxy
SDSSJ150634.27+013331.6 in the nearby NGC5846 group by the Virtual Observatory
(VO) workflow . This object (M_B = -15.98 mag, R_e = 0.24 kpc) becomes the
fifth cE where the spatially-resolved kinematics and stellar populations can be
obtained. We used archival HST WFPC2 images to demonstrate that its light
profile has a two-component structure, and integrated photometry from GALEX,
SDSS, UKIDSS, and Spitzer to build the multi-wavelength SED to constraint the
star formation history (SFH). We observed this galaxy with the PMAS IFU
spectrograph at the Calar-Alto 3.5m telescope and obtained two-dimensional maps
of its kinematics and stellar population properties using the full-spectral
fitting technique. Its structural, dynamical and stellar population properties
suggest that it had a massive progenitor heavily tidally stripped by NGC5846.Comment: 5 pages, 4 figure, 1 table. Accepted to MNRAS Letter
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