Revisiting the globular cluster systems of NGC3258 and NGC3268

We present a photometric study of NGC3258 and NGC3268 globular cluster systems (GCSs) with a wider spatial coverage than previous works. This allowed us to determine the extension of both GCSs, and obtain new values for their populations. In both galaxies, we found the presence of radial colour gradients in the peak of the blue globular clusters. The characteristics of both GCSs point to a large evolutionary history with a substantial accretion of satellite galaxies.Instituto de Astrofísica de La Plat

The merger remnant NGC3610 and its globular cluster system: a large-scale study

We present a photometric study of the prototypemerger remnant NGC3610 and its globular cluster (GC) system, based on new GEMINI/GMOS and ACS/HST archival images. Thanks to the large FOV of our GMOS data, larger than previous studies, we are able to detect a ‘classical’ bimodal GC colour distribution, corresponding to metal-poor and metalrich GCs, at intermediate radii and a small subsample of likely young clusters of intermediate colours, mainly located in the outskirts. The extent of the whole GC system is settled as about 40 kpc. The GC population is quite poor, about 500± 110members that corresponds to a low total specific frequency SN ∼ 0.8. The effective radii of a cluster sample are determined, including those of two spectroscopically confirmed young and metal-rich clusters, that are in the limit between GC and UCD sizes and brightness. The large-scale galaxy surface-brightness profile can be decomposed as an inner embedded disc and an outer spheroid, determining for both larger extents than earlier research (10 kpc and 30 kpc, respectively). We detect boxy isophotes, expected in merger remnants, and show a wealth of fine-structure in the surfacebrightness distribution with unprecedented detail, coincidentwith the outer spheroid. The lack of symmetry in the galaxy colour map adds a new piece of evidence to the recent merger scenario of NGC3610.Facultad de Ciencias Astronómicas y Geofísica

Globular cluster systems in low-luminosity early-type galaxies near the Fornax cluster centre

We present a photometric study of the globular cluster systems (GCSs) of the Fornax cluster galaxies NGC 1374, NGC 1379 and NGC 1387. The data consist of images from the wide-field MOSAIC imager of the Cerro Tololo Inter-American Observatory (CTIO) 4-m telescope, obtained with Washington C and Kron-Cousins R filters. The images cover a field of 36 × 36 arcmin2, corresponding to 200 × 200 kpc2 at the Fornax distance. Two of the galaxies, NGC 1374 and NGC 1379, are low-luminosity ellipticals while NGC 1387 is a low-luminosity lenticular. Their cluster systems are still embedded in the cluster system of NGC 1399. Therefore, the use of a large field is crucial and some differences to previous work can be explained by this. The colour distributions of all GCSs are bimodal. NGC 1387 presents a particularly distinct separation between red and blue clusters and an overproportionally large population of red clusters. The radial distribution is different for blue and red clusters, red clusters being more concentrated towards the respective galaxies. The different colour and radial distributions point to the existence of two globular cluster subpopulations in these galaxies. Specific frequencies are in the range SN = 1.4-2.4, smaller than the typical values for elliptical galaxies. These galaxies might have suffered tidal stripping of blue globular clusters by NGC 1399.Facultad de Ciencias Astronómicas y Geofísica

CCD photometry in the region of NGC 6994: the remains of an old open cluster

We present the results of BV(RI)KC CCD photometry down to V=21 mag in the region of NGC 6994. To our knowledge, no photometry has previously been reported for this object and we find evidences that it is a poor and sparse old open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the 3 arcmin originally assigned to it. We obtain a color excess EB-V = 0.07 ± 0.02 mag by means of the BVIC technique. Based on the theoretical isochrones from VandenBerg (1985) that are in better agreement with our data, we estimate for this cluster a distance from the Sun of 620 pc (V0 - MV = 9 ± 0.25 mag) and an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus, the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at about 350 pc below the Galactic plane. According to these results, NGC 6994 belongs to the old open cluster population located in the outer disk and at large distances from the Galactic plane, and must have suffered significant individual dynamical evolution, resulting in mass segregation and evaporation of low mass stars.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Globular cluster systems as tracers of the evolutionary history in NGC 3258 and NGC 3268

We present a new photometric study of NGC 3258 and NGC 3268 globular cluster systems (GCSs), using images in filters B, C, V, R, I and z', obtained from four different telescopes. The wide spatial coverage allows us to estimate the whole extension of both GCSs more precisely than in previous works, and new values for the richness of GC subpopulations. We find differences in the azimuthal distribution between blue (metal-poor) and red (metal-rich) globular clusters (GCs), and confirm that radial profiles flatten towards the centre of the galaxies. In both cases we detected a radial gradient in the colour peak of blue GCs which might be related to the construction of the GCSs. We analyse the similarities and differences in both GCSs, in the context of the possible evolutionary histories of the host galaxies. We also obtain photometric metallicities for a large number of GC candidates around NGC 3258, by applying multicolour-metallicity relations. These results confirm the bimodal metallicity distribution.Instituto de Astrofísica de La Plat

CCD photometry in the region of NGC 6994: the remains of an old open cluster

We present the results of BV(RI)KC CCD photometry down to V=21 mag in the region of NGC 6994. To our knowledge, no photometry has previously been reported for this object and we find evidences that it is a poor and sparse old open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the 3 arcmin originally assigned to it. We obtain a color excess EB-V = 0.07 ± 0.02 mag by means of the BVIC technique. Based on the theoretical isochrones from VandenBerg (1985) that are in better agreement with our data, we estimate for this cluster a distance from the Sun of 620 pc (V0 - MV = 9 ± 0.25 mag) and an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus, the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at about 350 pc below the Galactic plane. According to these results, NGC 6994 belongs to the old open cluster population located in the outer disk and at large distances from the Galactic plane, and must have suffered significant individual dynamical evolution, resulting in mass segregation and evaporation of low mass stars.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Footprints in the sand: What can globular clusters tell us about NGC 4753 past?

NGC 4753 is a bright (Mv~-22.3) lenticular galaxy. It is a very interesting target to test different theories of formation of lenticular galaxies, due to its low-density environment and complex structure. We perform the first comprehensive study of NGC4753 globular cluster system (GCS), using Gemini/GMOS and CTIO/MosaicII images. Our results indicate a rather poor GCS of ~1000 members. Its azimuthal distribution follows the shape of the galaxy bulge. The GC colour distribution is peculiar, presenting an intermediate subpopulation in addition to blue and red ones. This intermediate subgroup can be explained by a single stellar population with an age of 1.53 Gyr and 0.5 − 1 Zo. The GC specific frequency Sn = 1.3 +/- 0.15 is surprisingly low for a galaxy of its class. The GC luminosity function (GCLF) is also peculiar, with an excess of bright GCs compared to the expected gaussian distribution. The underlying galaxy body has significant substructure, with remnants of spiral arms, dust filaments, and isophote twisting. This, and the fact that NGC4753 hosted two type Ia SNe, support the possibility that the intermediate GC subpopulation may have originated during a recent merger, 1-3 Gyr ago.Instituto de Astrofísica de La Plat

Globular cluster systems as tracers of the evolutionary history in NGC 3258 and NGC 3268

We present a new photometric study of NGC 3258 and NGC 3268 globular cluster systems (GCSs), using images in filters B, C, V, R, I and z', obtained from four different telescopes. The wide spatial coverage allows us to estimate the whole extension of both GCSs more precisely than in previous works, and new values for the richness of GC subpopulations. We find differences in the azimuthal distribution between blue (metal-poor) and red (metal-rich) globular clusters (GCs), and confirm that radial profiles flatten towards the centre of the galaxies. In both cases we detected a radial gradient in the colour peak of blue GCs which might be related to the construction of the GCSs. We analyse the similarities and differences in both GCSs, in the context of the possible evolutionary histories of the host galaxies. We also obtain photometric metallicities for a large number of GC candidates around NGC 3258, by applying multicolour-metallicity relations. These results confirm the bimodal metallicity distribution.Instituto de Astrofísica de La Plat

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 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 Astrofísica de La Plat