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This work reports the detection of a multi peaked colour pattern in the integrated colours distribution of globular clusters associated to the giant elliptical galaxy NGC 4486, using Next Generation Virgo Survey data. This feature is imprinted on the well known bimodal colour distribution of these clusters. Remarkably, the pattern is similar to that found in previous works based on photometry from the HST Advanced Camera Virgo Survey, in less massive Virgo galaxies. This characteristic can be traced up to to 45 arcmin (217 Kpc) in galactocentric radius. This suggests that globular cluster formation in Virgo has been regulated, at least partially, by a collective process composed by several discrete events, working on spatial scales comparable to the size of the galaxy cluster. Furthermore, the presence of a similar colour pattern in NGC 5128, at the outskirsts of the Virgo Super-cluster, poses an intriguing question about the spatial scale of the phenomenon. The nature of the process that leads to the colour pattern is unknown. However, energetic events connected with galaxy or sub-galaxy cluster mergers and SMBH activity, in the early Universe, appear as possible candidates to explain an eventual enhancement/quenching of the globular clusters formation, reflected in the modulation of their integrated colours. Such events, presumably, may also have had an impact on the whole star formation history in Virgo galaxies., Comment: 18 pages, 30 figures

The presence of systematic modulations in the colour distributions in composite samples of globular clusters associated with galaxies in the Virgo and Fornax clusters has been reported in a previous work. In this paper we focus on the 27 brightest galaxies in Virgo, and in particular on NGC 4486, the dominant system in terms of globular cluster population. The new analysis includes $\sim$7600 cluster candidates brighter than g =24.5 (or T1$\sim$ 23.70). The results indicate the presence of the characteristic Virgo pattern in these galaxies and that this pattern is detectable over a galactocentric range from 3 to 30 Kpc in N GC 4486. This finding gives more support to the idea that the pattern has been the result of an external, still not identified phenomenon, capable of synchronizing the cluster formation in a kind of viral process, and on supra-galactic scales (also having, presumably, an impact on the overall star formation history in the entire Virgo cluster)., Comment: 16 pages, 39 figures

We present multi-object spectroscopy of the inner zone of the globular cluster (GC) system associated with the intermediate-age merger remnant NGC 1316. Using the multi-object mode of the GMOS camera, we obtained spectra for 35 GCs. We find pieces of evidence that the innermost GCs of NGC 1316 rotate almost perpendicular to the stellar component of the galaxy. In a second stage, we determined ages, metallicities and {\alpha}-element abundances for each GC present in the sample, through the measurement of different Lick/IDS indices and their comparison with simple stellar population models. We confirmed the existence of multiple GC populations associated with NGC 1316, where the presence of a dominant subpopulation of very young GCs, with an average age of 2.1 Gyr, metallicities between -0.5 < [Z/H] < 0.5 dex and {\alpha}-element abundances in the range -0.2 < [{\alpha}/Fe] < 0.3 dex, stands out. Several objects in our sample present subsolar values of [{\alpha}/Fe] and a large spread of [Z/H] and ages. Some of these objects could actually be stripped nuclei, possibly accreted during minor merger events. Finally, the results have been analyzed with the aim of describing the different episodes of star formation and thus provide a more complete picture about the evolutionary history of the galaxy. We conclude that these pieces of evidence could indicate that this galaxy has cannibalized one or more gas-rich galaxies, where the last fusion event occurred about 2 Gyr ago., Comment: 19 pages, 21 figures, 4 tables

The giant elliptical galaxy NGC 1316 is the brightest galaxy in the Fornax cluster, and displays a number of morphological features that might be interpreted as an intermediate age merger remanent ($\sim$3 Gyr). Based on the idea that globular clusters systems (GCS) constitute genuine tracers of the formation and evolution of their host galaxies, we conducted a spectroscopic study of approximately 40 globular clusters (GCs) candidates associated with this interesting galaxy. We determined ages, metallicities, and $\alpha$-element abundances for each GC present in the sample, through the measurement of different Lick indices and their subsequent comparison with simple stellar populations models (SSPs)., Comment: 5 pages, 3 figures

An analysis of globular cluster systems associated with galaxies included in the Virgo and Fornax HST Advanced Camera Surveys reveals distinct (g-z) colour modulation patterns. These features appear on composite samples of globular clusters and, most evidently, in galaxies with absolute magnitudes Mg in the range from -20.2 to -19.2. These colour modulations are also detectable on some samples of globular clusters in the central galaxies NGC 1399 and NGC 4486 (and confirmed on data sets obtained with different instruments and photometric systems), as well as in other bright galaxies in these clusters. After discarding field contamination, photometric errors and statistical effects, we conclude that these supra-galactic colour patterns are real and reflect some previously unknown characteristic. These features suggest that the globular cluster formation process was not entirely stochastic but included a fraction of clusters that formed in a rather synchronized fashion over large spatial scales, and in a tentative time lapse of about 1.5 Gy at redshifts z between 2 and 4. We speculate that the putative mechanism leading to that synchronism may be associated with large scale feedback effects connected with violent star forming events and/or with super massive black holes., Comment: 20 pages. 38 figures. 4 tables

Context. Ultra-compact dwarfs (UCDs) are stellar systems displaying colours and metallicities between those of globular clusters (GCs) and early-type dwarf galaxies, as well as sizes of Reff <= 100 pc and luminosities in the range -13.5 < MV < -11 mag. Although their origin is still subject of debate, the most popular scenarios suggest that they are massive star clusters or the nuclei of tidally stripped dwarf galaxies. Aims. NGC 5044 is the central massive elliptical galaxy of the NGC 5044 group. Its GC/UCD system is completely unexplored. Methods. In Gemini+GMOS deep images of several fields around NGC 5044 and in spectroscopic multi-object data of one of these fields, we detected an unresolved source with g'~20.6 mag, compatible with being an UCD. Its radial velocity was obtained with FXCOR and the penalized pixel-fitting (pPXF) code. To study its stellar population content, we measured the Lick/IDS indices and compared them with predictions of single stellar population models, and we used the full spectral fitting technique. Results. The spectroscopic analysis of the UCD revealed a radial velocity that agrees with the velocity of the elliptical galaxy NGC 5044. From the Lick/IDS indices, we have obtained a luminosity-weighted age and metallicity of 11.7+/-1.4 Gyr and [Z/H] = -0.79 +/- 0.04 dex, respectively, as well as [alpha/Fe] = 0.30 +/- 0.06. From the full spectral fitting technique, we measured a lower age (8.52 Gyr) and a similar total metallicity ([Z/H] = -0.86 dex). Conclusions. Our results indicate that NGC 5044-UCD1 is most likely an extreme GC (MV ~ -12.5 mag) belonging to the GC system of the elliptical galaxy NGC 5044., Comment: 5 pages, 4 figures. Accepted to be published in A&A

Observational and theoretical arguments support the idea that violent events connected with $AGN$ activity and/or intense star forming episodes have played a significant role in the early phases of galaxy formation at high red shifts. Being old stellar systems, globular clusters seem adequate candidates to search for the eventual signatures that might have been left by those energetic phenomena. The analysis of the colour distributions of several thousands of globular clusters in the Virgo and Fornax galaxy clusters reveals the existence of some interesting and previously undetected features. A simple pattern recognition technique, indicates the presence of "colour modulations", distinctive for each galaxy cluster. The results suggest that the globular cluster formation process has not been completely stochastic but, rather, included a significant fraction of globulars that formed in a synchronized way and over supra-galactic spatial scales., Comment: 9 pages; 9 figures

This paper presents Gemini-$gri'$ high quality photometry for cluster candidates in the field of NGC 1316 (Fornax A) as part of a study that also includes GMOS spectroscopy. A preliminary discussion of the photometric data indicates the presence of four stellar cluster populations with distinctive features in terms of age, chemical abundance and spatial distribution. Two of them seem to be the usually old (metal poor and metal rich) populations typically found in elliptical galaxies. In turn, an intermediate-age (5 Gyr) globular cluster population is the dominant component of the sample (as reported by previous papers). We also find a younger cluster population with a tentative age of $\approx$ 1 Gyr.

In recent years, a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilised discriminant, their stellar population properties. Based on new spectroscopy from 8-10m telescopes, we derive ages, metallicities, and [\alpha/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals larger than M32. Together with a literature compilation, 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 compact ellipticals (cEs) depart from the mass-metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultra-compact dwarfs (UCDs) changes at a few times $10^7$ M$_{\odot}$, which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in CSSs are paralleled only by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as CSSs previously being more massive and undergoing 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 internal escape velocities., Comment: 18 pages, 10 figures, accepted for publication in MNRAS

There has been significant controversy over the mechanisms responsible for forming compact stellar systems like ultra compact dwarfs (UCDs), with suggestions that UCDs are simply the high mass extension of the globular cluster (GC) population, or alternatively, the liberated nuclei of galaxies tidally stripped by larger companions. Definitive examples of UCDs formed by either route have been difficult to find, with only a handful of persuasive examples of stripped-nucleus type UCDs being known. In this paper we present very deep Gemini/GMOS spectroscopic observations of the suspected stripped nucleus UCD NGC 4546-UCD1 taken in good seeing conditions (< 0.7"). With these data we examine the spatially resolved kinematics and star formation history of this unusual object. We find no evidence of a rise in the central velocity dispersion of the UCD, suggesting that this UCD lacks a massive central black hole like those found in some other compact stellar systems, a conclusion confirmed by detailed dynamical modelling. Finally we are able to use our extremely high signal to noise spectrum to detect a temporally extended star formation history for this UCD. We find that the UCD was forming stars since the earliest epochs until at least 1-2 Gyr ago. Taken together these observations confirm that NGC 4546-UCD1 is the remnant nucleus of a nucleated dwarf galaxy that was tidally destroyed by NGC 4546 within the last 1-2 Gyr., Comment: 13 pages, 4 figures, accepted for publication in MNRAS, V2 updated to use new MNRAS style

We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster. Imaging of NGC 4649 was assembled from a recently-obtained HST/ACS mosaic, and new Subaru/Suprime-Cam and archival CFHT/MegaCam data. About 1200 sources were followed up spectroscopically using combined observations from three multi-object spectrographs: Keck/DEIMOS, Gemini/GMOS and MMT/Hectospec. We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than previous datasets and with a factor of 3 improvement in velocity precision. We confirm significant GC colour bimodality and find that the red GCs are more centrally concentrated, while the blue GCs are more spatially extended. We infer negative GC colour gradients in the innermost 20 kpc and flat gradients out to large radii. Rotation is detected along the galaxy major axis for all tracers: blue GCs, red GCs, galaxy stars and planetary nebulae. We compare the observed properties of NGC 4649 with galaxy formation models. We find that formation via a major merger between two gas-poor galaxies, followed by satellite accretion, can consistently reproduce the observations of NGC 4649 at different radii. We find no strong evidence to support an interaction between NGC 4649 and the neighbouring spiral galaxy NGC 4647. We identify interesting GC kinematic features in our data, such as counter-rotating subgroups and bumpy kinematic profiles, which encode more clues about the formation history of NGC 4649., Comment: 24 pages, 18 figures, accepted for publication in MNRAS

We revisit the color-magnitude relation (CMR) of the Virgo cluster early-type galaxies in order to explore its alleged non-linearity. To this aim, we reanalyze the relation already published from data obtained within the ACS Virgo Cluster Survey of the Hubble Space Telescope, and perform our own photometry and analysis of the images of the 100 early-type galaxies observed as part of this survey. In addition, we compare our results with those reported in the literature from data of the Sloan Digital Sky Survey. We have found that when the brightest galaxies and untypical systems are excluded from the sample, a linear relation arises in agreement with what is observed in other groups and clusters. The central regions of the brightest galaxies also follow this relation. In addition, we notice that Virgo contains at least four compact elliptical galaxies besides the well known object VCC 1297 (NGC 4486B). Their locations in the -luminosity diagram define a different trend to that followed by normal early-type dwarf galaxies, setting an upper limit in effective surface brightness and a lower limit in effective radius for their luminosities. Based on the distribution of different galaxy sub-samples in the color-magnitude and -luminosity diagrams we draw some conclusions on their formation and the history of their evolution., Comment: 21 pages, 4 figures, 2 tables. Accepted for publication in ApJ

We present Gemini griz photometry for 521 globular cluster (GC) candidates in a 5.5 x 5.5 arcmin field centered 3.8 arcmin to the south and 0.9 arcmin to the west of the center of the giant elliptical galaxy NGC 4486. All these objects have previously published (C-T1) photometry. We also present new (C-T1) photometry for 338 globulars, within 1.7 arcmin in galactocentric radius, which have (g-z) colors in the photometric system adopted by the Virgo Cluster Survey of the Advanced Camera for Surveys of the Hubble Space Telescope. These photometric data are used to define a self-consistent multicolor grid (avoiding polynomial fits) and preliminary calibrated in terms of two chemical abundance scales. The resulting multicolor color-chemical abundance relations are used to test GC chemical abundance distributions. This is accomplished by modelling the ten GC color histograms that can be defined in terms of the Cgriz bands. Our results suggest that the best fit to the GC observed color histograms is consistent with a genuinely bimodal chemical abundance distribution NGC(Z). On the other side, each (blue and red) GC subpopulation follows a distinct color-color relation., Comment: 12 pages, 21 figures, 8 tables. Accepted to be published in MNRAS

This paper presents further results from our spectroscopic study of the globular cluster (GC) system of the group elliptical NGC 3923. From observations made with the GMOS instrument on the Gemini South telescope, an additional 50 GC and Ultra Compact Dwarf (UCD) candidates have been spectroscopically confirmed as members of the NGC 3923 system. When the recessional velocities of these GCs are combined with the 29 GC velocities reported previously, a total sample of 79 GC/UCD velocities is produced. This sample extends to over 6 arcmin (>6 Re \sim30 kpc) from the centre of NGC 3923, and is used to study the dynamics of the GC system and the dark matter content of NGC 3923. It is found that the GC system of NGC 3923 displays no appreciable rotation, and that the projected velocity dispersion is constant with radius within the uncertainties. The velocity dispersion profiles of the integrated light and GC system of NGC 3923 are indistinguishable over the region in which they overlap. We find some evidence that the diffuse light and GCs of NGC 3923 have radially biased orbits within \sim130". The application of axisymmetric orbit-based models to the GC and integrated light velocity dispersion profiles demonstrates that a significant increase in the mass-to-light ratio (from M/Lv = 8 to 26) at large galactocentric radii is required to explain these observations. We therefore confirm the presence of a dark matter halo in NGC 3923. We find that dark matter comprises 17.5% of the mass within 1 Re, 41.2% within 2 Re, and 75.6% within the radius of our last kinematic tracer at 6.9 Re. The total dynamical mass within this radius is found to be 1.5 x 10^12 solar masses. In common with other studies of large ellipticals, we find that our derived dynamical mass profile is consistently higher than that derived by X-ray observations, by a factor of around 2., Comment: 17 pages, 10 figures, accepted for publication in MNRAS

As shown in previous works, globular clusters can be used to trace the overall structure of the diffuse stellar populations in early type galaxies if the number of clusters per unit stellar mass depends on metallicity. In this paper we further test this assumption in the galaxy NGC 4486 (M 87), by combining several data sources. The results show that globular clusters allow the mapping of the galaxy in terms of the surface brightness profile, integrated colour gradient, chemical abundance, and mass to luminosity ratios up to 1000 arcsec (or 80.4 kpc) from its centre (i.e. some 10 effective radii). The analysis indicates the presence of a dominant high metallicity bulge associated with the red globulars, whose ellipticity increases outwards, and of a more flattened low metallicity halo connected with the blue globulars. The chemical abundance gradient of the composite stellar population is remarkably similar to that inferred from X ray observations of hot gas. The mass-metallicity spectrum of the stellar population can, in principle, be understood in terms of inhomogeneous enrichment models. In turn, the distribution of the bluest GCs, and lowest metallicity halo stars, has an intriguing similarity with that of dark matter, a feature shared with NGC 1399. Also, in these two galaxies, the number of blue GCs per dark mass unit is identical within the errors, \approx 1.0(\pm0.3) \times 10^{-9} . The total stellar mass derived for NGC 4486 is 6.8(\pm1.1) \times 10^{11} M\odot with a baryonic mass fraction fb = 0.08(\pm 0.01)., Comment: 18 pages, 23 figures

This paper presents deep high quality photometry of globular cluster (GC) systems 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 GC candidates and unresolved field objects. Bimodal GC colour distributions are found in all five galaxies. Most of the GC systems appear bimodal even in the (g' -r') vs (r' -i') plane. A population of resolved/marginally resolved GC and Ultra Compact 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 that 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 \propto M^0.28\pm0.03 . This dependence was found using a new empirical (g' -i') vs [Z/H] relation which relies on an homogeneous sample of GC colours and metallicities. This paper also explores 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 ones. Evidence of galactocentric colour gradients is found in some of the GC systems, being 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] \propto L_B ^0.26\pm0.08, is present for the red GCs. An estimate of the total GC populations and specific frequency SN values is presented for NGC 3115, NGC 3379, NGC 3923 and NGC 4649., Comment: 23 pages, 13 figures and 9 tables. Tables A1 and A2 will be published in full online only. Accepted for publication in MNRAS

This paper explores if, and to what an extent, the stellar populations of early type galaxies can be traced through the colour distribution of their globular cluster systems. The analysis, based on a galaxy sample from the Virgo ACS data, is an extension of a previous approach that has been successful in the cases of the giant ellipticals NGC 1399 and NGC 4486, and assumes that the two dominant GC populations form along diffuse stellar populations sharing the cluster chemical abundances and spatial distributions. The results show that a) Integrated galaxy colours can be matched to within the photometric uncertainties and are consistent with a narrow range of ages; b) The inferred mass to luminosity ratios and stellar masses are within the range of values available in the literature; c) Most globular cluster systems occupy a thick plane in the volume space defined by the cluster formation efficiency, total stellar mass and projected surface mass density. The formation efficiency parameter of the red clusters shows a dependency with projected stellar mass density that is absent for the blue globulars. In turn, the brightest galaxies appear clearly detached from that plane as a possible consequence of major past mergers; d) The stellar mass-metallicity relation is relatively shallow but shows a slope change at $M_*\approx 10^{10} M_\odot$. Galaxies with smaller stellar masses show predominantly unimodal globular cluster colour distributions. This result may indicate that less massive galaxies are not able to retain chemically enriched intestellar matter., Comment: 19 pages, 10 figures

We present a technique to extract ultra-deep diffuse-light spectra from the standard multi-object spectroscopic observations used to investigate extragalactic globular cluster (GC) systems. This technique allows a clean extraction of the spectrum of the host galaxy diffuse light from the same slitlets as the GC targets. We show the utility of the method for investigating the kinematics and stellar populations of galaxies at radii much greater than usually probed in longslit studies, at no additional expense in terms of telescope time. To demonstrate this technique we present Gemini/GMOS spectroscopy of 29 GCs associated with the elliptical galaxy NGC 3923. We compare the measured stellar population parameters of the GC system with those of the spheroid of NGC 3923 at the same projected radii, and find the GCs to have old ages (> 10 Gyr), [alpha/Fe]~0.3 and a range of metallicities running from [Z/H] = -1.8 to +0.35. The diffuse light of the galaxy is found to have ages, metallicities and [alpha/Fe] abundance ratios indistinguishable from those of the red GCs., Comment: 15 pages, 9 figures, accepted for publication in MNRAS

NGC 4649 (M60) is one of a handful of giant Virgo ellipticals. We have obtained Gemini/GMOS spectra for 38 GCs associated with this galaxy. Applying the multi-index chi^2 minimisation technique of Proctor & Sansom (2002) with the single stellar population models of Thomas, Maraston & Korn (2004) we derive ages, metallicities and alpha-element abundance ratios. We find several young (2--3 Gyr old) super-solar metallicity GCs, while the majority are old (>10 Gyrs), spanning a range of metallicities from solar to [Z/H]=-2. At least two of these young GCs are at large projected radii of 17-20 kpc. The galaxy itself shows no obvious signs of a recent starburst, interaction or merger. A trend of decreasing alpha-element ratio with increasing metallicity is found., Comment: 12 pages, 4 figs, 6 tables, MNRAS accepted

We have obtained Gemini/GMOS spectra for 22 GCs associated with NGC 3379. We derive ages, metallicities and alpha-element abundance ratios from simple stellar population models using the multi-index chi^2 minimisation method of Proctor & Sansom (2002). All of these GCs are found to be consistent with old ages, i.e. >10 Gyr, with a wide range of metallicities. A trend of decreasing alpha-element abundance ratio with increasing metallicity is indicated. The projected velocity dispersion of the GC system is consistent with being constant with radius. Non-parametric, isotropic models require a significant increase in the mass-to-light ratio at large radii. This result is in contrast to that of Romanowsky et al. (2003) who find a decrease in the velocity dispersion profile as determined from planetary nebulae. Our constant dispersion requires a normal sized dark halo, although without anisotropic models we cannot rigorously determine the dark halo mass. A two-sided chi^2 test over all radii, gives a 2 sigma difference between the mass profile derived from our GCs compared to the PN-derived mass model of Romanowsky et al. (2003). However, if we restrict our analysis to radii beyond one effective radius and test if the GC velocity dispersion is consistently higher, we determine a >3 sigma difference between the mass models, and hence favor the conclusion that NGC 3379 does indeed have dark matter at large radii in its halo. (abridged), Comment: 25 pages, 10 figures, accepted MNRAS, 2 Notes added in proof

Globular cluster systems (GCS) frequently show a bi-modal distribution of the cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. In the particular case of NGC 1399 the results show that the galaxy brightness profile and colour gradient as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so called "blue" and "red" globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn=3.3 +/- 0.3 in the case of the red globulars and Sn=14.3 +/- 2.5 for the blue ones. We stress that this result is not necessarily conflicting with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about 6 times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X ray emiting hot gas associated with NGC 1399, is emphasized. The impact of a relatively unconspicuous low metallicity population, that shares the properties of the blue globulars, as a possible source of chemical enrichment early in the formation history of the galaxy is also briefly discussed., Comment: 15 pages; MNRAS (accepted; October 2004)

We present Sloan g and i imaging from the GMOS instrument on the Gemini North telescope for the globular cluster (GC) system around the Virgo galaxy NGC 4649 (M60). Our three pointings, taken in good seeing conditions, cover an area of about 90 sq. arcmins. We detect 2,151 unresolved sources. Applying colour and magnitude selection criteria to this source list gives 995 candidate GCs that is greater than 90% complete to a magnitude of i = 23.6, with little contamination from background galaxies. We find fewer than half a dozen potential Ultra Compact Dwarf galaxies around NGC 4649. Foreground extinction from the nearby spiral NGC 4647 is limited to be A_V < 0.1. We confirm the bimodality in the GC colour distribution found by earlier work using HST/WFPC2 imaging. As is commonly seen in other galaxies, the red GCs are concentrated towards the centre of the galaxy, having a steeper number density profile than the blue GC subpopulation. The varying ratio of red-to-blue GCs with radius can largely explain the overall GC system colour gradient. The underlying galaxy starlight has a similar density profile slope and colour to the red GCs. This suggests a direct connection between the galaxy field stars and the red GC subpopulation. We estimate a total GC population of 3700 +/- 900, with the uncertainty dominated by the extrapolation to larger radii than observed. This total number corresponds to a specific frequency S_N = 4.1 +/- 1.0. Future work will present properties derived from GMOS spectra of the NGC 4649 GCs., Comment: 20 pages, Latex, 14 figures, 2 tables, MNRAS in press

We present recent results from our long-term Gemini/GMOS study of globular clusters in early-type galaxies. To date, we have obtained photometry and spectroscopy for clusters in NGCs 3379, 4649, 524, 7332, and IC 1459. We find a clear bimodality in the NGC 4649 cluster colour distribution, with the fraction of blue/red clusters increasing with galactocentric radius. We derive ages and metallicities for 22 clusters in NGC 3379, finding that most of the clusters appear old (10-15 Gyr); however, there is a group of 4 metal-rich, younger clusters with ages of 2-6 Gyr. The NGC 3379 cluster velocity dispersion decreases with radius, as does the inferred (local) mass-to-light ratio: there is no evidence for a dark matter halo in NGC 3379 based on our globular cluster data., Comment: 3 pages, 2 figures, uses newpasp.sty (included). 'In press' for "Joint Discussion #6: Extragalactic Globular Clusters and their Host Galaxies", IAU General Assembly, July 2003. Editors: T. Bridges and D. Forbes

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'x36'. This is the largest area around this galaxy ever studied with CCD photometry. The cluster system of NGC 1399 is found to extend further 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 to the center than the blueclusters. 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 -1.85 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 outwards. The cluster system contains 6450+-700 clusters and the specific frequency is found to be 5.1+-1.2 in the V band. While NGC 1399 shows a pronounced color gradient. Using simple assumptions about the underlying population that formed during the same star formation event as the globular clusters, we presenta 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' 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 a high local specific frequency of around 10., Comment: 30 pages, 21 figures, accepted for publication in AJ

We present linear polarization in the V band for 77 stars in the field of the globular cluster 47 Tucanae (NGC 104), and for 14 bright-star-free regions, located along an elliptical isophotal contour of the cluster, as well as UBVRI measurements for the cluster nucleus. The observations show variable foreground polarization that, once removed, leaves marginally significant polarization residuals for the non-variable bright red giants. Although these residuals are small there is, however, a systematic trend in the sense that the larger ones are seen towards the south of the cluster (in a direction opposite to that of the cluster proper motion). In contrast, most of the variable stars do show significant intrinsic polarization. The behavior of the star-free regions is similar to that of the non-variable stars and sets an upper limit to the possible existence of a global pattern of scattered (and polarized) intra-cluster light in the V band. In turn, the multicolor observations of the cluster nucleus cannot be fitted with a Serkowski law and exhibit a polarization excess both in U and B. This polarization could be explained as a combination of the foreground interstellar component and another one arising in dust located in the nucleus and illuminated by a bright blue post-AGB star (at 48" from the cluster center). An inspection of a set of archive HST WFPC2 images reveals the presence of a number of dark patches in the innermost regions of the cluster. A prominent patch (some 5" by 3" in size) located at 12" from the cluster center and with a position angle (N to E) of 120 degrees, has a slightly different polarization, compared to that of the cluster nucleus, and appears as a good candidate to be identified as a dust globule within the cluster., Comment: AASTeX v5.0.2, Submitted to the Astronomical Journal, 20 pages (including title-page and tables.), 11 figures (16 PostScript files), 5 tables

A large number of early type galaxies are now known to possess blue and red subpopulations of globular clusters. We have compiled a database 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 colour 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. Futhermore, 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., Comment: 6 pages, Latex, 3 figures, 1 table, submitted to MNRAS