183 research outputs found
Large-scale study of the NGC 1399 globular cluster system in Fornax
We present a Washington C and Kron-Cousins R photometric study of the
globular cluster system of NGC 1399, the central galaxy of the Fornax cluster.
A large areal coverage of 1 square degree around NGC 1399 is achieved with
three adjoining fields of the MOSAIC II Imager at the CTIO 4-m telescope.
Working on such a large field, we can perform the first indicative
determination of the total size of the NGC 1399 globular cluster system. The
estimated angular extent, measured from the NGC 1399 centre and up to a
limiting radius where the areal density of blue globular clusters falls to 30
per cent of the background level, is 45 +/- 5 arcmin, which corresponds to 220
- 275 kpc at the Fornax distance. The bimodal colour distribution of this
globular cluster system, as well as the different radial distribution of blue
and red clusters, up to these large distances from the parent galaxy, are
confirmed. The azimuthal globular cluster distribution exhibits asymmetries
that might be understood in terms of tidal stripping of globulars from NGC
1387, a nearby galaxy. The good agreement between the areal density profile of
blue clusters and a projected dark-matter NFW density profile is emphasized.Comment: 9 pages, 9 figures. Accepted for publication in A&
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
S_N=3.0+-2.0 for NGC 3268 and S_N=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.Comment: 12 pages, accepted for publication in the A&
The globular cluster system of NGC 1316 : I. Wide-field photometry in the Washington system
Context. NGC 1316 (Fornax A) is a prominent merger remnant in the outskirts of the Fornax cluster. The bulge stellar population of NGC 1316 has a strong intermediate-age component. Studies of its globular cluster system may help to further refine its probably complex star formation history. Aims. 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. Methods. We used the MOSAIC II camera at the 4-m Blanco telescope at CTIO in the filters Washington C and Harris R. We identified globular cluster candidates and studied their color distribution and the structural properties of the system. In an appendix, we also remark on the morphology, present color maps, and present new models for the brightness and color profiles of the galaxy. Results. The cluster system is well confined to the optically visible outer contours of NGC 1316. There are about 640 cluster candidates down to R = 24 mag. The color distribution of the entire sample is unimodal, but the color distribution of bright subsamples in the bulge shows two peaks that, compared 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′. The outer cluster population shows an unimodal color distribution with a peak at C-R = 1.1, indicating a higher contribution of old, metal-poor clusters. However, their luminosity function does not show the expected turn-over, so the fraction of younger clusters is still significant. We find a pronounced concentration of blue cluster candidates in the area of Schweizer's L1-structure. Conclusions. Cluster formation in NGC 1316 has continued after an initial burst that is 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. In this model, the older, metal-rich pre-merger population has an age of 7 Gyr, contributes 90% of the bulge mass and 70% of the luminosity. Its properties are consistent with spiral galaxies, where star-bursts were triggered by major/minor mergers and/or close encounters.Instituto de AstrofĂsica de La Plat
The globular cluster system of NGC 1316. II - The extraordinary object SH2
SH2 has been described as an isolated HII-region, located about 6.5 arcmin
south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the
outskirts of the Fornax cluster of galaxies. We give a first, preliminary
description of the stellar content and environment of this remarkable object.
We used photometric data in the Washington system and HST photometry from the
Hubble Legacy Archive for a morphological description and preliminary aperture
photometry. Low-resolution spectroscopy provides radial velocities of the
brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not
a normal HII-region, ionized by very young stars. It contains a multitude of
star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is
striking. SH2 seems to be connected to an intermediate-age massive globular
cluster with a similar radial velocity, which itself is the main object of a
group of fainter clusters. Metallicity estimates from emission lines remain
ambiguous. The present data do not yet allow firm conclusions about the nature
or origin of SH2. It might be a dwarf galaxy that has experienced a burst of
extremely clustered star formation. We may witness how globular clusters are
donated to a parent galaxy.Comment: 5 pages, to appear in A&A, format slightly different from the printed
versio
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