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).

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 study the kinematics and dynamics of the globular cluster system of NGC 1399, the brightest elliptical galaxy near the center of the Fornax cluster of galaxies. The observational data consists of medium-resolution spectra, obtained at the Very Large Telescope with FORS2 and the Mask Exchange Unit (MXU). Our sample comprises 468 radial velocities in the magnitude range 20 < m R < 23. This is the largest sample of globular cluster velocities around any galaxy obtained so far. Typical velocity uncertainties are 50 km s À1 , significantly improving on earlier samples. The radial range is 2 0 < r < 9 0 , corresponding to 11 kpc to 50 kpc of galactocentric distance. The shape of the velocity distribution of the sample is compatible with being a Gaussian distribution. However, under moderate error selection, a slight asymmetry is visible between high and low radial velocities. We find bright clusters with radial velocities below 800 km s À1 , while they are not found at the corresponding highvelocity side above 2000 km s À1 . There is the possibility that unbound clusters and/or objects in the foreground contaminate the NGC 1399 cluster sample. Under strong error selection, practically no objects are found with velocities lower than 800 km s À1 or higher than 2000 km s À1 . Since the extreme velocities influence the velocity dispersion considerably, uncertainty regarding the exact value of the dispersion remains. With the above velocity limits, we derive a projected velocity dispersion for the total sample of 274 AE 9 km s À1 which within the uncertainties remains constant over the entire radial range. Without any velocity restriction, it increases to 325 km s À1 . Guided by the bimodal color distribution of clusters, we distinguish between red clusters (CÀR > 1:6) and blue clusters (CÀR < 1:6), and find velocity dispersions for these groups of 255 AE 13 and 291 AE 14 km s À1 , respectively, again radially constant. Any possible rotation of either of these cluster populations is below the detection limit, with the exception of a weak signature of rotation for the blue clusters more distant than 6 0 . Spherical models point to a circular velocity of 419 AE 30 km s À1 , assuming isotropy for the red clusters. This value is constant out to 40 kpc. The inferred dark halo potential can be well represented by a logarithmic potential. A halo of the NFW type also provides a good fit to the observations. The orbital structure of the clusters can only be weakly constrained. It is consistent with isotropy for the red clusters and a slight tangential bias for the blue clusters. Some mass profiles derived from X-ray analyses do not agree with a constant circular velocity within our radial range, irrespective of its exact value. Interpreting the extreme low radial velocities as space velocities of bound clusters near their pericentric distances would require an extension of the cluster system of at least 200 kpc. Implications for formation scenarios of the cluster system are briefly commented on.

In this paper, we present deep high‐quality photometry of globular cluster systems (GCSs) belonging to five early‐type galaxies, covering a range of mass and environment. Photometric data were obtained with the Gemini North and Gemini South telescopes in the filter passbands g′, r′ and i′. The combination of these filters with good seeing conditions allows an excellent separation between globular cluster (GC) candidates and unresolved field objects. In fact, our previously published spectroscopic data indicate a contamination level of only ∼10 per cent in our sample of GC candidates. Bimodal GC colour distributions are found in all five galaxies. Most of the GCSs appear bimodal even in the (g′−r′) versus (r′−i′) plane. A population of resolved/marginally resolved GC and ultracompact dwarf candidates was found in all the galaxies. A search for the so‐called ‘blue tilt’ in the colour–magnitude diagrams reveals that NGC 4649 clearly shows this phenomenon, although no conclusive evidence was found for the other galaxies in the sample. This ‘blue tilt’ translates into a mass–metallicity relation given by Z∝M0.28 ±0.03. This dependence was found using a new empirical (g′−i′) versus [Z/H] relation, which relies on an homogeneous sample of GC colours and metallicities. In this paper, we also explore the radial trends in both colour and surface density for the blue (metal‐poor) and red (metal‐rich) GC subpopulations. As usual, the red GCs show a steeper radial distribution than the blue GCs. Evidence of galactocentric colour gradients is found in some of the GCSs, which is more significant for the two S0 galaxies in the sample. Red GC subpopulations show similar colours and gradients to the galaxy halo stars in their inner region. A GC mean colour–galaxy luminosity relation, consistent with [Z/H]∝L0.26 ±0.08B, is present for the red GCs. Estimates of the total GC populations and specific frequency SN values are presented for NGC 3115, 3923 and 4649.

A B S T R A C TA large number of early-type galaxies are now known to possess blue and red subpopulations of globular clusters. We have compiled a data base of 28 such galaxies exhibiting bimodal globular cluster colour distributions. After converting to a common V±I colour system, we investigate correlations between the mean colour of the blue and red subpopulations with galaxy velocity dispersion. We support previous claims that the mean colours of the blue globular clusters are unrelated to their host galaxy. They must have formed rather independently of the galaxy potential they now inhabit. The mean blue colour is similar to that for halo globular clusters in our Galaxy and M31. The red globular clusters, on the other hand, reveal a strong correlation with galaxy velocity dispersion. Furthermore, in well-studied galaxies the red subpopulation has similar, and possibly identical, colours to the galaxy halo stars. Our results indicate an intimate link between the red globular clusters and the host galaxy; they share a common formation history. A natural explanation for these trends would be the formation of the red globular clusters during galaxy collapse.

This paper explores the quantitative connection between globular clusters and the 'diffuse' stellar population of the galaxies they are associated with. Both NGC 1399 and NGC 4486 (M87) are well suited for this kind of analysis due to their large globular cluster populations.The main assumption of our Monte Carlo based models is that each globular cluster is formed along with a given diffuse stellar mass that shares the same spatial distribution, chemical composition and age. The main globular cluster subpopulations, that determine the observed bimodal colour distribution, are decomposed avoiding a priori parametric (e.g. Gaussian) fits and using a new colour (C − T 1 )-metallicity relation. The eventual detectability of a 'blue' tilt in the colour-magnitude diagrams of the blue globular cluster subpopulation is also addressed.A successful link between globular clusters and the stellar galaxy halo is established by assuming that the number of globular clusters per associated diffuse stellar mass t is a function of total abundance [Z/H] and behaves as t = γ exp(−δ[Z/H]) (i.e. increases when abundance decreases).The simulations allow the prediction of a surface brightness profile for each galaxy through these two free parameters' approximation. The γ , δ parameters that provide the best fit to the observed profiles in the B band, in turn, determine several features, namely, large-scale halo colour gradients, globular cluster-halo colour offset, clusters' cumulative specific frequencies, and stellar metallicity distributions, that compare well with observations.The results suggest the co-existence of two distinct stellar populations characterized by widely different metallicities and spatial distributions. One of these populations (connected with the blue globular clusters) is metal poor, highly homogeneous, exhibits an extended spatial distribution and becomes more evident at large galactocentric radius contributing with some 20 per cent of the total stellar mass. In turn, the stellar population associated with the red globular clusters is extremely heterogeneous and dominates the inner region of both galaxies.Remarkably, and although the cluster populations of these galaxies exhibit detectable differences in colour distribution, the δ parameter that determines the shape of the brightness profiles of both galaxies has the same value, δ ≈ 1.1 to 1.2 ± 0.1.

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Over the last decade and a half a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between those displayed by classical globular clusters (GCs) and those of true galaxies. This has led to significant debate about their exact nature. An important, and until now, underutilized discriminant in this debate is provided by in the stellar population properties.Here we present the single stellar population equivalent ages, metallicities, and [α/Fe] of 29 CSSs, based on new spectroscopy from 8-10m class telescopes. With the sample compiled from the AIMSS project and a search for CSSs in the Sloan Digital Sky Survey (Huxor et al.) we sample CSSs ranging from GCs with sizes of merely a few parsec to compact ellipticals (cEs) larger than M32. Together with a literature compilation of comparison samples, this provides a panoramic view of the stellar population characteristics of early-type systems.We find that the CSSs are predominantly more metal rich than typical galaxies at the same stellar mass. At high mass, the cEs depart from the mass-metallicity relation of massive early-type galaxies, which continuously forms a sequence with dwarf galaxies. At lower mass, we find a transition in the ultracompact dwarf (UCD) metallicity distribution at a few times 10 7 M , which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in UCDs and cEs are only paralleled by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as an indication that they were more massive at an earlier time and underwent tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS escape velocities.