We present a photometric investigation of the globular cluster population of NGC 1399, the central galaxy in the Fornax cluster, in Washington C and Kron R filters within a field of 36 0 Â 36 0 , corresponding to about 200 Â 200 kpc at the Fornax distance. This is the largest area around this galaxy ever studied with CCD photometry. The cluster system of NGC 1399 is found to extend farther than 100 kpc away from the galaxy. The color distribution exhibits a pronounced bimodality. Within a radial distance of about 55 kpc, the red clusters are more strongly concentrated toward the center than the blue clusters. At larger radii, the surface density profiles of the clusters are indistinguishable and match well the distribution of the galaxy light. Over the entire radial distance range, the surface brightness profile of NGC 1399 can be very well fitted by a power law with an exponent of À1.85 and a core radius of 3>3. No steepening of the luminosity profile can be detected at large radii. We suggest that the power-law profile of NGC 1399 results from the galaxy being embedded in a large dark matter halo, which prevents the stellar density profile from steepening outward. The cluster system contains 6450 AE 700 clusters and the specific frequency is found to be 5.1 AE 1.2 in the V band. While NGC 1399 shows a pronounced color gradient the nearby comparison galaxy NGC 1404 does not show such a gradient. Using simple assumptions about the underlying population that formed during the same star formation event as the globular clusters, we present a model in which we use radially changing local specific frequencies for the red and blue subpopulations to fit the observations. We find that within 7 0 the required specific frequency of the blue clusters alone is a factor of approximately 3 larger than that of the red ones. Outside this radius, however, both populations have the same high local specific frequency of around 8 and 13 (blue and red clusters, respectively).

Context. The internal dynamics of ultra-compact dwarf galaxies (UCDs) has attracted increasing attention, with most of the UCDs studied to date located in the Virgo cluster. Aims. Our aim is to perform a comprehensive census of the internal dynamics of UCDs in the Fornax cluster, and to shed light on the nature of the interface between star clusters and galaxies. Methods. We obtained high-resolution spectra of 23 Fornax UCDs with -10.4 > M V > −13.5 mag (10 6 < M/M < 10 8 ), using FLAMES/Giraffe at the VLT. This is the largest homogeneous data set of UCD internal dynamics assembled to date. We derive dynamical M/L ratios for 15 UCDs covered by HST imaging. Results. In the M V -σ plane, UCDs with M V < −12 mag are consistent with the extrapolated Faber-Jackson relation for luminous elliptical galaxies, while most of the fainter UCDs are closer to the extrapolated globular cluster (GC) relation. At a given metallicity, Fornax UCDs have, on average, M/L ratios lower by 30-40% than Virgo UCDs, suggesting possible differences in age or dark matter content between Fornax and Virgo UCDs. For our sample of Fornax UCDs we find no significant correlation between M/L ratio and mass. We combine our data with available M/L ratio measurements of compact stellar systems with 10 4 < M/M < 10 8 M, and normalise all M/L estimates to solar metallicity. We find that UCDs (M 2 × 10 6 M ) have M/L ratios twice as large as GCs (M 2 × 10 6 M ). We argue that dynamical evolution has probably had only a small effect on the current M/L ratios of objects in the combined sample, implying that stellar population models tend to under-predict dynamical M/L ratios of UCDs and over-predict those of GCs. Considering the scaling relations of stellar spheroids, we find that UCDs align well along the "Fundamental Manifold". UCDs can be considered the small-scale end of the galaxy sequence in this context. The alignment for UCDs is especially clear for r e 7 pc, which corresponds to dynamical relaxation times that exceed a Hubble time. In contrast, globular clusters exhibit a broader scatter and do not appear to align along the manifold. Conclusions. We argue that UCDs are the smallest dynamically un-relaxed stellar systems, with M 2×10 6 M and 7 r e /pc 100. Future studies should aim at explaining the elevated M/L ratios of UCDs and the environmental dependence of their properties.

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.

We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded u, g and i-band image obtained with the DECam wide-field camera mounted on the 4meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the Next Generation Fornax Survey (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii 0.1 < r e < 2.8 kpc and average effective surface brightness values 22.0 < µ i < 28.0 mag arcsec −2 . We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters. We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of M i = −8.0 mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of > 75% at luminosities brighter than M i ≃ −15.0 mag to 0% at luminosities fainter than M i ≃ −10.0 mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below ∼100 kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.

We present a new calibration of the Stroemgren metallicity index m 1 using red giant (RG) stars in a sample of Galactic globular clusters (GGCs: M92, M13, NGC 1851, 47 Tuc) that cover a broad range in metallicity (−2.2 ≤ [Fe/H] ≤ −0.7), are marginally affected by reddening uncertainties (E(B-V ) ≤ 0.04) and for which accurate u, v, b, y Stroemgren photometry is available to well below 1 Based in part on observations collected with the 1.54m Danish telescope operated at ESO (La Silla) and with the Nordic Optical Telescope (NOT) operated at La Palma (Spain).-2the turnoff region. The main difference between the new empirical metallicityindex-color (MIC) relations and similar relations available in the literature is that we have adopted the u-y and v-y colors instead of the b-y color. These colors present a stronger sensitivity to effective temperature, and the MIC relations show a linear and well-defined slope. The net difference between photometric estimates and spectroscopic measurements, for RG stars in five GGCs: M71, NGC 288, NGC 362, NGC 6397, NGC 6752, is 0.04 ± 0.03 dex with σ = 0.11 dex. We also apply the new MIC relations to a sample of field stars for which spectroscopic metallicity (−2.4 ≤ [Fe/H] ≤ −0.5), accurate Strömgren photometry, and reddening estimates (Anthony-Twarog & Twarog 1994 are all available. We find that the difference between photometric estimates and spectroscopic measurements is on average −0.14 ± 0.01 dex, with σ = 0.17 dex. We also provide two independent sets of MIC relations based on evolutionary models that have been transformed into the observational plane by adopting either semi-empirical or theoretical color-temperature relations (CTRs). We apply the semi-empirical α−enhanced MIC relations to the nine GCs and find that the difference between photometric estimates and spectroscopic measurements is 0.04 ± 0.03 dex, with σ = 0.10 dex. A similar agreement is also found for the sample of field stars, and indeed the difference is −0.09 ± 0.03 dex, with σ = 0.19 dex. The difference between metallicity estimates based on theoretical scaled-solar and spectroscopic measurements −0.11±0.03 dex, with σ = 0.14 dex for the nine GGCs and −0.24 ± 0.03 dex, with σ = 0.15 dex for the field stars. On the whole, current findings support the evidence that new Strömgren MIC relations provide metallicity estimates with an intrinsic accuracy better than 0.2 dex.