52 research outputs found
Intra-cluster globular clusters around NGC 1399 in Fornax?
Aims. We investigate whether the globular clusters (GCs) in the recently published sample of GCs in the Fornax cluster by Bergond and coworkers are indeed intra-cluster objects. Methods. We combine their catalogue of radial velocity measurements with our CTIO MOSAIC photometry in the Washington system and analyse the relation of metal-poor and metal-rich GCs with their host galaxies. Results. The metal-rich GCs appear to be kinematically associated with their respective host galaxies. The vast majority of the metal-poor GCs found in between the galaxies of the Fornax cluster have velocities that are consistent with their being members of the very extended NGC 1399 GC system. We find that when the sample is restricted to the most accurate velocity measurements, the GC velocity dispersion profile can be described with a mass model derived for the NGC 1399 GC system, within 80kpc. We identify one "vagrant" GC whose radial velocity suggests that it is not bound to any galaxy unless its orbit has a very large apogalactic distance.Facultad de Ciencias Astronómicas y Geofísica
VLT Spectroscopy of Globular Cluster Systems, I. The Photometric and Spectroscopic Dataset
We present Lick line-index measurements of extragalactic globular clusters in
seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585, 5846, and 7192)
with different morphological types (E-S0) located in field and group/cluster
environments. High-quality spectra were taken with the FORS2 instrument at
ESO's Very Large Telescope. About 50% of our data allow an age resolution dt/t
~ 0.3 and a metallicity resolution ~0.25-0.4 dex, depending on the absolute
metallicity. Globular cluster candidates are selected from deep B, V, R, I, K
FORS2/ISAAC photometry with 80-100% success rate inside one effective radius.
Using combined optical/near-infrared colour-colour diagrams we present a method
to efficiently reduce fore-/background contamination down to <10%. We find
clear signs for bi-modality in the globular cluster colour distributions of NGC
1380, 3115, and 3585. The colour distributions of globular clusters in NGC
2434, 3379, 5846, and 7192 are consistent with a broad single-peak
distribution. For the analysed globular cluster systems the slopes of projected
radial surface density profiles, of the form Sigma(R) ~ R^-Gamma, vary between
~0.8 and 2.6. Using globular clusters as a tracer population we determine total
dynamical masses of host galaxies out to large radii (~1.6 - 4.8 Reff). For the
sample we find masses in the range ~8.8*10^10 Msolar up to ~1.2*10^12 Msolar.
The line index data presented here will be used in accompanying papers of this
series to derive ages, metallicities and abundance ratios. A compilation of
currently available high-quality Lick index measurements for globular clusters
in elliptical, lenticular, and late-type galaxies is provided and will serve to
augment the current data set. [abridged]Comment: A&A accepted, 42 page
The Chemistry of Extragalactic Globular Clusters
We present preliminary results of VLT/FORS spectroscopy of globular clusters
in nearby early-type galaxies. Our project aims at studying the chemistry and
determine the ages of globular cluster (sub-)populations. First results
indicate that the different galaxies host from little to significant
intermediate-age populations, and that the latter have alpha-element over iron
ratios closer to solar than the old population that show an alpha-element
enhancement similar to the diffuse stellar light.Comment: 4 pages (incl 2 figures) to appear in the proceedings of
"Extragalactic Globular Cluster Systems", ed.M.Kissler-Patig, Springer; see
also related contributions by T.H.Puzia and M.Hempel et a
Remarks on the properties of elliptical galaxies in modified Newtonian dynamics
Two incorrect arguments against MOND in elliptical galaxies could be that the
equivalent circular velocity curves tend to become flat at much larger
accelerations than in spiral galaxies, and that the Newtonian dark matter halos
are more concentrated than in spirals. Here, we compare published scaling
relations for the dark halos of elliptical galaxies to the scaling relations
expected for MONDian phantom halos. We represent the baryonic content of
galaxies by spherical profiles, and their corresponding MONDian phantom halos
by logarithmic halos. We then derive the surface densities, central densities,
and phase space densities and compare them with published scaling relations. We
conclude that it is possible to get flat circular velocity curves at high
acceleration in MOND, and that this happens for baryonic distributions
described by Jaffe profiles in the region where the circular velocity curve is
flat. Moreover, the scaling relations of dark halos of ellipticals are
remarkably similar to the scaling relations of phantom halos of MOND.Comment: Accepted for publication in A and
The globular cluster systems of NGC 3258 and NGC 3268 in the Antlia cluster
The Antlia galaxy cluster is the third nearest galaxy cluster after Virgo and Fornax. We used the wide-field MOSAIC camera of the 4-m CTIO telescope to search in the brightest cluster galaxies for globular cluster systems, which were detected in the two larger ellipticals - NGC 3258 and NGC 3268. These galaxies each contain several thousand clusters; NGC 3258 more than NGC 3268. The color distributions of the globular cluster systems are clearly bimodal. The peak colors agree with those of other ellipticals. The radial number density profiles of the globular cluster systems are indistinguishable for the two galaxies and no difference in the distribution of red and blue clusters - as observed in other elliptical galaxies - can be seen. The light profile of NGC 3268 appears to be similar to that of NGC 1399, the central galaxy of the Fornax cluster. NGC 3258 has a light profile which is steeper at large radii. Both galaxies exhibit color gradients, becoming bluer outwards. In NGC 3268, the color and morphology in the inner 3″ indicate the presence of an inner dusty disk. The globular cluster systems closely trace the galaxy light in the studied radial regime. The elongation of the cluster systems of both galaxies is approximately aligned at large radii with the connecting axis of the two galaxies. We find specific frequencies within a radial range of 4′ of SN - 3.0 ± 2.0 for NGC 3268 and SN = 6.0 ± 2.5 for NGC 3258. As a byproduct resulting from surveying our wide-field frames, we describe a strange absorption feature in the Antlia spiral galaxy NGC 3269, which we argue might be a tiny galactic dust cloud projected onto NGC 3269.Facultad de Ciencias Astronómicas y Geofísica
The paucity of globular clusters around the field elliptical NGC 7507
Context. There is strong evidence that globular cluster systems (GCSs) of massive galaxies are largely assembled by infall/accretion processes. Therefore, we expect the GCSs of isolated elliptical galaxies to be poor. Although not completely isolated, NGC 7507 is a massive field elliptical galaxy with an apparently very low dark matter content. Aims. We determine the richness, the colour distribution, and the structural properties of the GCS of NGC 7507. Methods. We performed wide-field Washington photometry with data obtained with the MOSAIC II camera at the 4m-Blanco telescope (CTIO, Chile). Results. The GCS is very poor with SN ≈ 0.6. We identify three subpopulations with peaks at (C - T1) colours of 1.21, 1.42, and 1.72. The bluest population may represent the old, metal-poor component. This interpretation is supported by its shallow density profile. The red population is more concentrated, resembling the galaxy light. The intermediate-colour population is strongly peaked in colour, and we interpret this population as the signature of a starburst whose age depends on the metallicity, but should be quite old, since no signatures of a merger are identifiable. In addition, we find a main sequence in the stellar foreground population, which we attribute to the Sagittarius dwarf tidal stream. Conclusions. The extrordinarily poor GCS of NGC 7507, a massive elliptical galaxy, is an illustration of how important the environmental conditions are for producing rich GCSs.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
The dark matter halo of NGC 1399 - CDM or MOND?
Context: Central galaxies in galaxy clusters may be key discriminants in the competition between the cold dark matter (CDM) paradigm and modified Newtonian dynamics (MOND).
Aims: We investigate the dark halo of NGC 1399, the central galaxy of the Fornax cluster, out to a galactocentric distance of 80 kpc.
Methods: The data base consists of 656 radial velocities of globular clusters obtained with MXU/VLT and GMOS/Gemini, which is the largest sample so far for any galaxy. We performed a Jeans analysis for a non-rotating isotropic model.
Results: An NFW halo with the parameters rs = 50 kpc and gs = 0.0065 M⊙/pc3 provides a good description of our data, fitting well to the X-ray mass. More massive halos are also permitted that agree with the mass of the Fornax cluster as derived from galaxy velocities. We compare this halo with the expected MOND models under isotropy and find that additional dark matter on the order of the stellar mass is needed to get agreement. A fully radial infinite globular cluster system would be needed to change this conclusion.
Conclusions: Regarding CDM, we cannot draw firm conclusions. To really constrain a cluster wide halo, more data covering a larger radius are necessary. The MOND result appears as a small-scale variant of the finding that MOND in galaxy clusters still needs dark matter.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
VLT Spectroscopy of Globular Clusters in Low Surface Brightness Dwarf Galaxies
We present VLT/FORS2 spectroscopic observations of globular clusters (GCs) in
five low surface brightness (LSB) dwarf galaxies: KK211 and KK221, which are
both dwarf spheroidal satellites (dSph) of NGC 5128, dSph KK84 located close to
the isolated S0 galaxy NGC 3115, and two isolated dwarf irregular (dIrr)
galaxies UGC 3755 and ESO 490-17. Our sample is selected from the Sharina et
al. (2005) database of Hubble Space Telescope WFPC2 photometry of GC candidates
in dwarf galaxies. For objects with accurate radial velocity measurements we
confirm 26 as genuine GCs out of the 27 selected candidates from our WFPC2
survey. Lick absorption line indices in the spectra of confirmed GCs and the
subsequent comparison with SSP model predictions show that all confirmed GCs in
dSphs are old, except GC KK211-3-149 (6 +/- 2 Gyr), which we consider to be the
nucleus of KK211. GCs in UGC 3755 and ESO 490-17 show a large spread in ages
ranging from old objects (t > 10 Gyr) to clusters with ages around 1 Gyr. Most
of our sample GCs have low metallicities [Z/H] <= -1. Two relatively metal-rich
clusters with [Z/H] ~ -0.3 are likely to be associated with NGC 3115. Our
sample GCs show in general a complex distribution of alpha-element enhancement
with a mean [alpha/Fe]=0.19 +/-0.04 derived with the chi2 minimization
technique and 0.18+/-0.12 dex computed with the iterative approach. These
values are slightly lower than the mean [alpha/Fe]=0.29+/-0.01 for typical
Milky Way GCs. We compare other abundance ratios with those of Local Group GCs
and find indications for systematic differences in N and Ca abundance. The
specific frequencies, S_N, of our sample galaxies are in line with the
predictions of a simple mass-loss model for dwarf galaxies and compare well
with S_N values found for dwarf galaxies in nearby galaxy clusters.Comment: accepted for publication in Ap
Intra-cluster globular clusters around NGC 1399 in Fornax?
Aims. We investigate whether the globular clusters (GCs) in the recently published sample of GCs in the Fornax cluster by Bergond and coworkers are indeed intra-cluster objects. Methods. We combine their catalogue of radial velocity measurements with our CTIO MOSAIC photometry in the Washington system and analyse the relation of metal-poor and metal-rich GCs with their host galaxies. Results. The metal-rich GCs appear to be kinematically associated with their respective host galaxies. The vast majority of the metal-poor GCs found in between the galaxies of the Fornax cluster have velocities that are consistent with their being members of the very extended NGC 1399 GC system. We find that when the sample is restricted to the most accurate velocity measurements, the GC velocity dispersion profile can be described with a mass model derived for the NGC 1399 GC system, within 80kpc. We identify one "vagrant" GC whose radial velocity suggests that it is not bound to any galaxy unless its orbit has a very large apogalactic distance.Facultad de Ciencias Astronómicas y Geofísica
The globular cluster system of NGC1316. I. Wide-field photometry in the Washington system
NGC 1316 (Fornax A) is a prominent merger remnant in the outskirts of the
Fornax cluster. The cluster system has not yet been studied in its entirety. We
therefore present a wide-field study of the globular cluster system of NGC
1316, investigating its properties in relation to the global morphology of NGC
1316. We used the MOSAIC II camera at the 4-m Blanco telescope at CTIO in the
filters Washington C and Harris R. We identify globular cluster candidates and
study their color distribution and the structural properties of the system. In
an appendix, we also make morphological remarks, present color maps, and
present new models for the brightness and color profiles of the galaxy. The
cluster system is well confined to the optically visible outer contours of NGC
1316. The color distribution of the entire sample is unimodal, but the color
distribution of bright subsamples in the bulge shows two peaks that, by
comparison with theoretical Washington colors with solar metallicity,
correspond to ages of about 2 Gyr and 0.8 Gyr, respectively. We also find a
significant population of clusters in the color range 0.8 < C-R < 1.1 which
must be populated by clusters younger than 0.8 Gyr, unless they are very
metal-poor. The color interval 1.3 < C-R < 1.6 hosts the bulk of
intermediate-age clusters which show a surface density profile with a sharp
decline at about 4 arcmin. The outer cluster population shows an unimodal color
distribution with a peak at C-R=1.1, indicating a larger contribution of old,
metal-poor clusters. Their luminosity function does not show the expected
turn-over, so the fraction of younger clusters is still significant. Cluster
formation in NGC 1316 has continued after an initial burst, presumably related
to the main merger. A toy model with two bursts of ages 2 Gyr and 0.8 Gyr is
consistent with photometric properties and dynamical M/L-values.Comment: 19 pages, to appear in Astronomy and Astrophysics, abstract abridged,
format slightly different from the printed versio
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