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Aims. The initial cluster mass function (ICMF) in spiral discs is constrained and compared with data for old globular clusters and young clusters in starbursts.

Aims. We obtained VLT/FLAMES+UVES high-resolution, fibre-fed spectroscopy of five young massive clusters (YMCs) in M 83 (NGC 5236). This forms the basis of a pilot study testing the feasibility of using fibre-fed spectroscopy to measure the velocity dispersions of several clusters simultaneously, in order to determine their dynamical masses. In principle, this reduces the telescope time required to obtain a statistically significant sample of dynamical cluster masses. These can be used to assess the long-term survivability of YMCs by comparing their dynamical and photometric masses, which are necessary to ascertain the potential evolution of YMCs into second-generation globular clusters.

Context.Until now, only one planetary nebula (PN) has been known in the Fornax dwarf spheroidal galaxy.

Aims.We study a peculiar object with a projected position close to the nucleus of M 51. It is unusually large for a star cluster in M 51 and we therefore investigate the three most likely options to explain this object: (a) a background galaxy, (b) a cluster in the disk of M 51 and (c) a cluster in M 51, but in front of the disk.

Context.Size measurements of young star clusters are valuable tools to put constraints on the formation and early dynamical evolution of star clusters.

Context.Star clusters are present in almost all types of galaxies. Here we investigate the star cluster population in the low-luminosity, unperturbed spiral galaxy NGC 45, which is located in the nearby Sculptor group. Both the old (globular) and young star-cluster populations are studied.

Context.During an analysis of optical spectra of 80 young star clusters in several nearby spiral galaxies, [$\ion{O}{iii}$] and [$\ion{N}{ii}$] emission lines were noted in some cases. Three of these emission line sources are associated with clusters older than 30 Myr, and are identified as likely planetary nebula (PN) candidates.

Context.We present the first dynamical study of the globular cluster system of NGC 4636. It is the southernmost giant elliptical galaxy of the Virgo cluster and is claimed to be extremely dark matter dominated, according to X-ray observations.

We introduce a method to relate a possible truncation of the star cluster mass function at the high mass end to the shape of the cluster luminosity function (LF). We compare the observed LFs of five galaxies containing young star clusters with synthetic cluster population models with varying initial conditions. The LF of the SMC, the LMC and NGC 5236 are characterized by a power-law behavior $N\, {\rm d} L \propto L^{-\alpha}\, {\rm d} L$, with a mean exponent of $\langle \alpha\rangle = 2.0 \pm 0.2$. This can be explained by a cluster population formed with a constant cluster formation rate, in which the maximum cluster mass per logarithmic age bin is determined by the size-of-sample effect and therefore increases with log (age/yr). The LFs of NGC 6946 and M 51 are better described by a double power-law distribution or a Schechter function. When a cluster population has a mass function that is truncated below the limit given by the size-of-sample effect, the total LF shows a bend at the magnitude of the maximum mass, with the age of the oldest cluster in the population, typically a few Gyr due to disruption. For NGC 6946 and M 51 this suggests a maximum mass of $ M_{\rm max} = 0.5{-}1\times10^6~ M_{\odot}$, although the bend is only a 1–2 σdetection. Faint-ward of the bend the LF has the same slope as the underlying initial cluster mass function and bright-ward of the bend it is steeper. This behavior can be well explained by our population model. We compare our results with the only other galaxy for which a bend in the LF has been observed, the “Antennae” galaxies (NGC 4038/4039). There the bend occurs brighter than in NGC 6946 and M 51, corresponding to a maximum cluster mass of $ M_{\rm max} = 1.3{-}2.5\times10^6\, M_{\odot}$. Hence, if the maximum cluster mass has a physical limit, then it can vary between different galaxies. The fact that we only observe this bend in the LF in the “Antennae” galaxies, NGC 6946 and M 51 is because there are enough clusters available to reach the limit. In other galaxies there might be a physical limit as well, but the number of clusters formed or observed is so low, that the LF is not sampled up to the luminosity of the bend. The LF can then be approximated with a single power-law distribution, with an index similar to the initial mass function index.

We present the luminosity function (LF) of star clusters in M 51 based on HST/ACSobservations taken as part of the Hubble Heritage project. The clusters are selected based on their size and with the resulting 5990 clusters we present one of the largest cluster samples of a single galaxy. We find that the LF can be approximated with a double power-law distribution with a break around MV= -8.9. On the bright side the index of the power-law distribution is steeper ($\alpha = 2.75$) than on the faint-side ($\alpha = 1.93$), similar to what was found earlier for the “Antennae” galaxies. The location of the bend, however, occurs about 1.6 mag fainter in M 51. We confront the observed LF with the model for the evolution of integrated properties of cluster populations of Gieles et al. (2006, A&A, accepted), which predicts that a truncated cluster initial mass function would result in a bend in, and a double power-law behaviour of, the integrated LF. The combination of the large field-of view and the high star cluster formation rate of M 51 make it possible to detect such a bend in the LF. Hence, we conclude that there exists a fundamental upper limit to the mass of star clusters in M 51. Assuming a power-law cluster initial mass function with exponentional cut-off of the form $N\, {\rm d} M \propto M^{-\beta}\,\exp(-M/M_{\rm C})\, {\rm d} M$, we find that $M_{\rm C} = 10^5\, M_{\odot}$. A direct comparison with the LF of the “Antennae” suggests that there $M_{\rm C} = 4\times10^5\, M_{\odot}$.

We study the globular cluster (GC) system of the Virgo giant elliptical galaxy NGC 4365, using new wide-field K-band imaging from the ESO 3.5 m New Technology Telescope, archive Vand Iimaging from FORS1 on the ESO VLT and HST/WFPC2+ACS data. As in most other large ellipticals, the GC colour distribution has (at least) two peaks, but the colours of the red GCs appear more strongly weighted towards intermediate colours compared to most other large ellipticals and the integrated galaxy light. The intermediate-color/red peak may itself be composed of two sub-populations, with clusters of intermediate colours more concentrated towards the centre of the galaxy than both the blue and red GCs. Nearly all GCs in our sample fall along a well-defined narrow sequence in the ($V\!-\!K$, $V\!-\!I$) two-colour diagram, with an offset towards red $V\!-\!K$and/or blue $V\!-\!I$colours compared to simple stellar population models for old ages. This has in the past been interpreted as evidence for an intermediate-age population of GCs. The offset is however seen for nearly all metal-rich clusters within the $5\arcmin\times5\arcmin$SOFI field, not just those of intermediate colours. We combine our VIKdata with previously published spectroscopy resulting in a sample of 25 GCs with both spectroscopy and photometry. The differences between observed and model colour–metallicity relations are consistent with the offsets observed in the two-colour diagram, with the metal-rich GCs being too red (by ${\approx}0.2$mag) in $V\!-\!K$and too blue (by ${\approx}0.05$mag) in $V\!-\!I$compared to the models at a given metallicity. These offsets cannot easily be explained as an effect of younger ages. We further compare the colour–metallicity relation for GCs in NGC 4365with previously published data for NGC 3115and the Sombrero galaxy, both of which are believed from spectroscopic studies to host exclusively old GC populations, and find the colour–metallicity relations for all three galaxies to be very similar. We review the available evidence for intermediate-age GCs in NGC 4365and conclude that, while this cannot be definitively ruled out, an alternative scenario is more likely whereby all the GCs are old but the relative number of intermediate-metallicity GCs is greater than typical for giant ellipticals. The main obstacle to reaching a definitive conclusion is the lack of robust calibrations of integrated spectral and photometric properties for stellar populations with near-solar metallicity. In any case, it is puzzling that the significant intermediate-colour GC population in NGC 4365is not accompanied by a corresponding shift of the integrated galaxy light towards bluer colours.

Using new data from the UVES spectrograph on the ESO Very Large Telescope and archive images from the Hubble Space Telescope, we have measured projected velocity dispersions and structural parameters for two bright young star clusters in the nearby spiral galaxy NGC 5236. One cluster is located near the nuclear starburst of NGC 5236, at a projected distance of 440 pc from the centre, while the other is located in the disk of the galaxy at a projected galactocentric distance of 2.3 kpc. We estimate virial masses for the two clusters of $(4.2\pm0.7)\times10^5~\mbox{$M_{\odot}$}$and $(5.2\pm0.8)\times10^5~\mbox{$M_{\odot}$}$and ages (from broad-band photometry) of $10^{7.1\pm0.2}$years and $10^{8.0\pm0.1}$years, respectively. Comparing the observed mass-to-light (M/L) ratios with simple stellar population models, we find that the data for both clusters are consistent with a Kroupa-type stellar mass function (MF). In particular, we rule out any MF with a significantly lower M/L ratio than the Kroupa MF, such as a Salpeter-like MF truncated at a mass of 1$~\mbox{$M_{\odot}$}$or higher. These clusters provide a good illustration of the fact that massive, globular cluster-like objects (“super star clusters”) can form at the present epoch even in the disks of seemingly normal, undisturbed spiral galaxies.

A search for stellar clusters has been carried out in 18 nearby spiral galaxies, using archive images from the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. All of the galaxies have previously been imaged from the ground in UBVI. A catalogue of structural parameters, photometry and comments based on visual inspection of the clusters is compiled and used to investigate correlations between cluster structure, environment, age and mass. Least-squares fits to the data suggest correlations between both the full-width at half-maximum (FWHM) and half-light radius ($R_\mathrm{eff}$) of the clusters and their masses (M) at about the $3\sigma$level. Although both relations show a large scatter, the fits have substantially shallower slopes than for a constant-density relation (size $\propto$$M^{1/3}$). However, many of the youngest clusters have extended halos which make the $R_\mathrm{eff}$determinations uncertain. There is no evidence for galaxy-to-galaxy variations in the mean cluster sizes. In particular, the mean sizes do not appear to depend on the host galaxy star formation rate surface density. 
Many of the youngest objects (age $< 10^7$years) are located in strongly crowded regions, and about 1/3–1/2 of them are double or multiple sources. The HST images are also used to check the nature of cluster candidates identified in a previous ground-based survey. The contamination rate in the ground-based sample is generally less than about 20%, but some cluster identifications remain ambiguous because of crowding even with HST imaging, especially for the youngest objects.

We present new accurate CCD uvbylight curves for the LMC eclipsing binaries HV 982 and HV 12578, and for the SMC systems HV 1433 and HV 11284 obtained at the Danish 1.5 m telescope at ESO, La Silla. The light curves were derived from DoPHOT photometry, and typical accuracies are between 0.007 and 0.012 mag per point. Standard uvbyindices have also been established for each binary, primarily for determination of interstellar reddening and absorption. For HV 982 and HV 12578, accurate photometric elements have been established. Both systems consist of two detached components of comparable sizes in an eccentric orbit. Adopting the spectroscopic elements given by Fitzpatrick et al. ([CITE]) for HV 982, we derive absolute dimensions of its components which agree well with their results. A distance modulus of $V_0-M_V = 18.63 \pm 0.08$is obtained, corresponding to a distance of $53.2 \pm 2.0$kpc, which is in formal agreement with (although slightly larger than) their determination. HV 1433 and HV 11284 both consist of two rather close, deformed and quite different stars. As the mass ratios between the components (and their rotation rates) are not known, definitive photometric elements can not yet be obtained, but we present a sample of possible photometric solutions. In a series of forthcoming papers we will combine our uvbyobservations with high-dispersion spectra from the UVES spectrograph on the ESO Very Large Telescope (VLT) and present absolute dimensions, chemical abundances and distances for selected LMC and SMC systems, including HV 12578 and refined results for HV 982.

We describe the results of a long-slit spectroscopic study of an unusual star complex in the nearby spiral galaxy NGC 6946 using the SAO 6 m telescope and the Keck 10 m telescope. The complex resembles a circular bubble 600 pc in diameter with a young super star cluster (SSC) near the center. The kinematics of ionized gas is studied through Hαemission with several slit positions. Position–velocity diagrams show two distinct features with high speed motions. One is an irregularly shaped region to the east of the SSC, 270 pc in size, in which most of the Hαemission is blue shifted by 120 km s-1, and another is a 350 pc shell centered on the SSC with positive and negative velocity shifts of 60 km s-1. Balmer and $\ion{He}{i}$absorption lines in the SSC give an age of 12–13 Myr, which is consistent with the photometric age but significantly older than the kinematic ages of the high speed regions. The energetics of the SSC and its interaction with the environment are considered. The expansion energies exceed 1052ergs, but the power outputs from winds and supernova in the SSC are large enough to account for this. The intensities of Balmer, [$\ion{N}{ii}$], and [$\ion{S}{ii}$] emission lines within and around the complex indicate that shock excitation makes a significant contribution to the emission from the most energetic region.

A detailed description is given of the data analysis leading to the discovery of young massive star clusters (YMCs) in a sample of 21 nearby galaxies. A new useful tool, ishape, for the derivation of intrinsic shape parameters of compact objects is presented, and some test results are shown. Completeness tests for the cluster samples are discussed, and ishapeis used to estimate cluster sizes. Half-light radii of 0-20 pc are derived for clusters in 2 of the most cluster-rich galaxies, NGC 1313 and NGC 5236, which is within the range spanned by globular clusters in the Milky Way and by YMCs in the LMC and some starburst galaxies. Photometric data for all clusters, along with positions and estimated half-light radii, are tabulated.

Development of acquired resistance to antiestrogens is a major clinical problem in endocrine treatment of breast cancer patients. The IGF system plays a profound role in many cancer types, including breast cancer. Thus, overexpression and/or constitutive activation of the IGF-I receptor (IGF-IR) or different components of the IGF-IR signaling pathway have been reported to render breast cancer cells less estrogen dependent and capable of sustaining cell proliferation in the presence of antiestrogens. In this study, growth of the antiestrogen-sensitive human breast cancer cell line MCF-7 was inhibited by treatment with IGF-IR-neutralizing antibodies. In contrast, IGF-IR-neutralizing antibodies had no effect on growth of two different antiestrogen-resistant MCF-7 sublines. A panel of antiestrogen-resistant cell lines was investigated for expression of IGF-IR and either undetectable or severely reduced IGF-IR levels were observed. No increase in insulin receptor substrate 1 (IRS-1) or total PKB/Akt (Akt) was detected in the resistant cell lines. However, a significant increase in phosphorylated Akt (pAkt) was found in four of six antiestrogen-resistant cell lines. Overexpression of pAkt was associated with increased Akt kinase activity in both a tamoxifen- and an ICI 182,780-resistant cell line. Inhibition of Akt phosphorylation by the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin or the Akt inhibitor SH-6 (structurally modified phosphatidyl inositol ether liquid analog PIA 6) resulted in a more pronounced growth inhibitory effect on the antiestrogen-resistant cells compared with the parental cells, suggesting that signaling via Akt is required for antiestrogen-resistant cell growth in at least a subset of our antiestrogen-resistant cell lines. PTEN expression and activity was not decreased in cell lines overexpressing pAkt. Our data demonstrate that Akt is a target for treatment of antiestrogen-resistant breast cancer cell lines and we suggest that antiestrogen-resistant breast cancer patients may benefit from treatment targeted to inhibit Akt signaling.

Aims.We present colour–magnitude diagrams (CMDs) of young massive star clusters in several galaxies located well beyond the Local Group. The richness of these clusters allows us to obtain large samples of post-main sequence stars and test how well the observed CMDs are reproduced by canonical stellar isochrones.

Context.Recent studies have started to cast doubt on the assumption that most stars are formed in clusters. Observational studies of field stars and star cluster systems in nearby galaxies can lead to better constraints on the fraction of stars forming in clusters. Ultimately this may lead to a better understanding of star formation in galaxies, and galaxy evolution in general.

Context.Some photometric studies of extragalactic globular cluster (GC) systems using the optical and near-infrared colour combination have suggested the presence of a large fraction of intermediate-age (2−8 Gyr) GCs.

Context. It is generally assumed that a large fraction of stars are initially born in clusters. However, a large fraction of these disrupt on short timescales and the stars end up belonging to the field. Understanding this process is of paramount importance if we wish to constrain the star formation histories of external galaxies using star clusters.Aims. We attempt to understand the relation between field stars and star clusters by simultaneously studying both in a number of nearby galaxies. Methods. As a pilot study, we present results for the late-type spiral NGC 4395 using HST/ACS and HST/WFPC2 images. Different detection criteria were used to distinguish point sources (star candidates) and extended objects (star cluster candidates). Using a synthetic CMD method, we estimated the star formation history. Using simple stellar population model fitting, we calculated the mass and age of the cluster candidates.Results. The field star formation rate appears to have been roughly constant, or to have possibly increased by up to about a factor of two, for ages younger than ~300 Myr within the fields covered by our data. Our data do not allow us to constrain the star formation histories at older ages. We identify a small number of clusters in both fields. Neither massive (>105$M_\odot$) clusters nor clusters with ages ≥1 Gyr were found in the galaxy and we found few clusters older than 100 Myr.Conclusions. Based on our direct comparison of field stars and clusters in NGC 4395, we estimate the ratio of star formation rate in clusters that survive for 107to 108years to the total star formation to be Γ~ 0.03. We suggest that this relatively low Γvalue is caused by the low star formation rate of NGC 4395.

Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (≥10 Gyr) and metal poor ([Fe/H] ~ -1.4), and three intermediate age (1–2 Gyr) and more metal rich ([Fe/H] ~ - 0.4) globular clusters in the LMC. We measured the line strengths of the $\ion{Na}{i}$, $\ion{Ca}{i}$and 12CO (2–0) absorption features. The $\ion{Na}{i}$index decreases with increasing age and decreasing metallicity of the clusters. The $D_{\rm CO}$index, used to measure the 12CO (2–0) line strength, is significantly reduced by the presence of carbon-rich TP-AGB stars in the globular clusters with age ~1 Gyr. This is in contradiction to the predictions of the stellar population models of Maraston (2005, MNRAS, 362, 799). We find that this disagreement is due to the different CO absorption strength of carbon-rich Milky Way TP-AGB stars used in the models and the LMC carbon stars in our sample. For globular clusters with age ≥2 Gyr we find $D_{\rm CO}$index measurements consistent with the model predictions.