A population-based case-control study on social factors and risk of testicular germ cell tumours

Objectives Incidence rates for testicular cancer have risen over the last few decades. Findings of an association between the risk of testicular cancer and social factors are controversial. The association of testicular cancer and different indicators of social factors were examined in this study.<p></p> Design Case–control study.<p></p> Setting Population-based multicentre study in four German regions (city states Bremen and Hamburg, the Saarland region and the city of Essen).<p></p> Participants The study included 797 control participants and 266 participants newly diagnosed with testicular cancer of which 167 cases were classified as seminoma and 99 as non-seminoma. The age of study participants ranged from 15 to 69 years.<p></p> Methods Social position was classified by educational attainment level, posteducational training, occupational sectors according to Erikson-Goldthorpe-Portocarrero (EGP) and the socioeconomic status (SES) on the basis of the International SocioEconomic Index of occupational status (ISEI). ORs and corresponding 95% CIs (95% CIs) were calculated for the whole study sample and for seminoma and non-seminoma separately.<p></p> Results Testicular cancer risk was modestly increased among participants with an apprenticeship (OR=1.7 (95% CI 1.0 to 2.8)) or a university degree (OR=1.6 (95% CI 0.9 to 2.8)) relative to those whose education was limited to school. Analysis of occupational sectors revealed an excess risk for farmers and farm-related occupations. No clear trend was observed for the analyses according to the ISEI-scale.<p></p> Conclusions Social factors based on occupational measures were not a risk factor for testicular cancer in this study. The elevated risk in farmers and farm-related occupations warrants further research including analysis of occupational exposures.<p></p&gt

Star Cluster collisions - a formation scenario for the Extended Globular Cluster Scl-dE1 GC1

Recent observations of the dwarf elliptical galaxy Scl-dE1 (Sc22) in the Sculptor group of galaxies revealed an extended globular cluster (Scl-dE1 GC1), which exhibits an extremely large core radius of about 21.2 pc. The authors of the discovery paper speculated on whether this object could reside in its own dark matter halo and/or if it might have formed through the merging of two or more star clusters. In this paper, we present N-body simulations to explore thoroughly this particular formation scenario. We follow the merger of two star clusters within dark matter haloes of a range of masses (as well as in the absence of a dark matter halo). In order to obtain a remnant which resembles the observed extended star cluster, we find that the star formation efficiency has to be quite high (around 33 per cent) and the dark matter halo, if present at all, has to be of very low mass, i.e. raising the mass to light ratio of the object within the body of the stellar distribution by at most a factor of a few. We also find that expansion of a single star cluster following mass loss provides another viable formation path. Finally, we show that future measurements of the velocity dispersion of this system may be able to distinguish between the various scenarios we have explored.Comment: accepted by MNRAS, 9 pages, 2 figures, 9 table

Mass modelling globular clusters in the Gaia era: a method comparison using mock data from an N-body simulation of M 4

As we enter a golden age for studies of internal kinematics and dynamics of Galactic globular clusters (GCs), it is timely to assess the performance of modelling techniques in recovering the mass, mass profile, and other dynamical properties of GCs. Here, we compare different mass-modelling techniques (distribution function (DF)-based models, Jeans models, and a grid of N-body models) by applying them to mock observations from a star-by-star N-body simulation of the GC M 4 by Heggie. The mocks mimic existing and anticipated data for GCs: surface brightness or number density profiles, local stellar mass functions, line-of-sight velocities, and Hubble Space Telescope-and Gaia-like proper motions. We discuss the successes and limitations of the methods. We find that multimass DF-based models, Jeans, and N-body models provide more accurate mass profiles compared to single-mass DF-based models. We highlight complications in fitting the kinematics in the outskirts due to energetically unbound stars associated with the cluster ('potential escapers', captured neither by truncated DF models nor by N-body models of clusters in isolation), which can be avoided with DF-based models including potential escapers, or with Jeans models. We discuss ways to account for mass segregation. For example, three-component DF-based models with freedom in their mass function are a simple alternative to avoid the biases of single-mass models (which systematically underestimate the total mass, half-mass radius, and central density), while more realistic multimass DF-based models with freedom in the remnant content represent a promising avenue to infer the total mass and the mass function of remnants

The Tidal Tails of NGC 5466

The study of substructure in the stellar halo of the Milky Way has made a lot of progress in recent years, especially with the advent of surveys like the Sloan Digital Sky Survey. Here, we study the newly discovered tidal tails of the Galactic globular cluster NGC 5466. By means of numerical simulations, we reproduce the shape, direction and surface density of the tidal tails, as well as the structural and kinematical properties of the present-day NGC 5466. Although its tails are very extended in SDSS data (> 45 degrees), NGC 5466 is only losing mass slowly at the present epoch and so can survive for probably a further Hubble time. The effects of tides at perigalacticon and disc crossing are the dominant causes of the slow dissolution of NGC 5466, accounting for about 60 % of the mass loss over the course of its evolution. The morphology of the tails provides a constraint on the proper motion -- the observationally determined proper motion has to be refined (within the stated error margins) to match the location of the tidal tails.Comment: MNRAS, in pres

Black holes and core expansion in massive star clusters

We present the results from realistic N-body modelling of massive star clusters in the Magellanic Clouds. We have computed eight simulations with N ~ 10^5 particles; six of these were evolved for at least a Hubble time. The aim of this modelling is to examine the possibility of large-scale core expansion in massive star clusters and search for a viable dynamical origin for the radius-age trend observed for such objects in the Magellanic Clouds. We identify two physical processes which can lead to significant and prolonged cluster core expansion: mass-loss due to rapid stellar evolution in a primordially mass segregated cluster, and heating due to a retained population of stellar-mass black holes. These two processes operate over different time-scales - the former occurs only at early times and cannot drive core expansion for longer than a few hundred Myr, while the latter typically does not begin until several hundred Myr have passed but can result in core expansion lasting for many Gyr. We investigate the behaviour of these expansion mechanisms in clusters with varying degrees of primordial mass segregation and in clusters with varying black hole retention fractions. In combination, the two processes can lead to a wide variety of evolutionary paths on the radius-age plane, which fully cover the observed cluster distribution and hence define a dynamical origin for the radius-age trend in the Magellanic Clouds. We discuss the implications of core expansion for various aspects of globular cluster research, as well as the possibility of observationally inferring the presence of a population of stellar-mass black holes in a cluster.Comment: Accepted for publication in MNRA

Mechanism for the Suppression of Intermediate-Mass Black Holes

A model for the formation of supermassive primordial black holes in galactic nuclei with the simultaneous suppression of the formation of intermediate-mass black holes is presented. A bimodal mass function for black holes formed through phase transitions in a model with a "Mexican hat" potential has been found. The classical motion of the phase of a complex scalar field during inflation has been taken into account. Possible observational manifestations of primordial black holes in galaxies and constraints on their number are discussed.Comment: 12 pages, 2 figure

Escaping stars from young low-N clusters

With the use of N-body calculations the amount and properties of escaping stars from low-N (N = 100 and 1000) young embedded star clusters prior to gas expulsion are studied over the first 5 Myr of their existence. Besides the number of stars also different initial radii and binary populations are examined as well as virialised and collapsing clusters. It is found that these clusters can loose substantial amounts (up to 20%) of stars within 5 Myr with considerable velocities up to more than 100 km/s. Even with their mean velocities between 2 and 8 km/s these stars will still be travelling between 2 and 30 pc during the 5 Myr. Therefore can large amounts of distributed stars in star-forming regions not necessarily be counted as evidence for the isolated formation of stars.Comment: 10 pages, 10 figures, accepted for publication by MNRA

Shock waves in strongly coupled plasmas

Shock waves are supersonic disturbances propagating in a fluid and giving rise to dissipation and drag. Weak shocks, i.e., those of small amplitude, can be well described within the hydrodynamic approximation. On the other hand, strong shocks are discontinuous within hydrodynamics and therefore probe the microscopics of the theory. In this paper we consider the case of the strongly coupled N=4 plasma whose microscopic description, applicable for scales smaller than the inverse temperature, is given in terms of gravity in an asymptotically $AdS_5$ space. In the gravity approximation, weak and strong shocks should be described by smooth metrics with no discontinuities. For weak shocks we find the dual metric in a derivative expansion and for strong shocks we use linearized gravity to find the exponential tail that determines the width of the shock. In particular we find that, when the velocity of the fluid relative to the shock approaches the speed of light $v\to 1$ the penetration depth $\ell$ scales as $\ell\sim (1-v^2)^{1/4}$. We compare the results with second order hydrodynamics and the Israel-Stewart approximation. Although they all agree in the hydrodynamic regime of weak shocks, we show that there is not even qualitative agreement for strong shocks. For the gravity side, the existence of shock waves implies that there are disturbances of constant shape propagating on the horizon of the dual black holes.Comment: 47 pages, 8 figures; v2:typos corrected, references adde

A large population of ultra-compact dwarf galaxies in the Hydra I cluster

We performed a large spectroscopic survey of compact, unresolved objects in the core of the Hydra I galaxy cluster (Abell 1060), with the aim of identifying ultra-compact dwarf galaxies (UCDs), and investigating the properties of the globular cluster (GC) system around the central cD galaxy NGC 3311. We obtained VIMOS medium resolution spectra of about 1200 candidate objects with apparent magnitudes 18.5 < V < 24.0 mag, covering both the bright end of the GC luminosity function and the luminosity range of all known UCDs. By means of spectroscopic redshift measurements, we identified 118 cluster members, from which 52 are brighter than M_V = -11.0 mag, and can therefore be termed UCDs. The brightest UCD in our sample has an absolute magnitude of M_V = -13.4 mag (corresponding to a mass of > 5 x 10^7 M_sun) and a half-light radius of 25 pc. This places it among the brightest and most massive UCDs ever discovered. Most of the GCs/UCDs are both spatially and dynamically associated to the central cD galaxy. The overall velocity dispersion of the GCs/UCDs is comparable to what is found for the cluster galaxies. However, when splitting the sample into a bright and a faint part, we observe a lower velocity dispersion for the bright UCDs/GCs than for the fainter objects. At a dividing magnitude of M_V = -10.75 mag, the dispersions differ by more than 200 km/s, and up to 300 km/s for objects within 5 arcmin around NGC 3311. We interpret these results in the context of different UCD formation channels, and conclude that interaction driven formation seems to play an important role in the centre of Hydra I.Comment: 18 pages, 17 figures, accepted for publication in A&

Evidence for Environmentally Dependent Cluster Disruption in M83

Using multi-wavelength imaging from the Wide Field Camera 3 on the Hubble Space Telescope we study the stellar cluster populations of two adjacent fields in the nearby face-on spiral galaxy, M83. The observations cover the galactic centre and reach out to ~6 kpc, thereby spanning a large range of environmental conditions, ideal for testing empirical laws of cluster disruption. The clusters are selected by visual inspection to be centrally concentrated, symmetric, and resolved on the images. We find that a large fraction of objects detected by automated algorithms (e.g. SExtractor or Daofind) are not clusters, but rather are associations. These are likely to disperse into the field on timescales of tens of Myr due to their lower stellar densities and not due to gas expulsion (i.e. they were never gravitationally bound). We split the sample into two discrete fields (inner and outer regions of the galaxy) and search for evidence of environmentally dependent cluster disruption. Colour-colour diagrams of the clusters, when compared to simple stellar population models, already indicate that a much larger fraction of the clusters in the outer field are older by tens of Myr than in the inner field. This impression is quantified by estimating each cluster's properties (age, mass, and extinction) and comparing the age/mass distributions between the two fields. Our results are inconsistent with "universal" age and mass distributions of clusters, and instead show that the ambient environment strongly affects the observed populations.Comment: 6 pages, 3 figures, MNRAS in pres