R. C. Brüns

Publications (3)4.9 Total impact

• Article: Popping star clusters as building blocks of the Milky Way’s thick disc

  P. Assmann, M. Fellhauer, P. Kroupa, R. C. Brüns, R. Smith
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  ABSTRACT: It is widely believed that star clusters form with low star formation efficiencies. With the onset of stellar winds by massive stars or finally when the first supernova blows off, the residual gas is driven out of the embedded star cluster. Due to this fact, a large number, if not all, of the stars become unbound and disperse in the gravitational potential of the galaxy. In this context, Kroupa suggested a new mechanism for the emergence of thickened galactic discs. Massive star clusters add kinematically hot components to the galactic field populations, building up, in this way, the Galactic thick disc as well. In this work, we perform, for the first time, numerical simulations to investigate this scenario for the formation of the Galactic discs of the Milky Way (MW). We find that a significant kinematically hot population of stars may be injected into the disc of a galaxy such that a thick disc emerges. For the MW, the star clusters that formed the thick disc must have had masses of about 106 M⊙.
  Monthly Notices of the Royal Astronomical Society 07/2011; 415(2):1280 - 1289. · 4.90 Impact Factor
• Source

  Available from: Pavel Kroupa

  Article: A New Formation Scenario for the Milky Way Cluster NGC 2419

  R C Brüns, P Kroupa
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  ABSTRACT: We present a new formation scenario for NGC 2419, which is one of the most lumi-nous, one of the most distant, and as well one of the most extended globular clusters of the Milky Way. We propose that NGC 2419 is the remnant of a merged star cluster complex, which was possibly formed during an interaction between a gas-rich galaxy and the Milky Way. To test this hypothesis, we performed numerical simulations of 27 different models of star cluster complexes (CCs) moving on a highly eccentric orbit in the Galactic halo. We vary the CC mass, the CC size, and the initial distribution of star clusters in the CC to analyze the influence of these parameters on the resulting objects. In all cases, the vast majority of star clusters merged into a stable object. The derived parameters mass, absolute V-band magnitude, effective radius, velocity disper-sion and the surface brightness profile are, for a number of models, in good agreement with those observed for NGC 2419. Despite the large range of CC sizes, the effective radii of the merger objects are constrained to a relatively small interval. A turnover in the r eff vs. M encl space leads to degenerate states, i.e. relatively compact CCs can produce an object with the same structural parameters as a more massive and larger CC. In consequence, a range of initial conditions can form a merger object comparable to NGC 2419 preventing us to pinpoint the exact parameters of the original CC, which formed NGC 2419. We conclude that NGC 2419 can be well explained by the merged cluster complex scenario. Some of the recently discovered stellar streams in the Galactic halo might be related to the parent galaxy, which produced the cluster complex in our scenario. Measurements of the proper motion of NGC 2419 are necessary to prove an association with one of the stellar streams.
  02/2011;
• Source

  Available from: Pavel Kroupa

  Article: Faint Fuzzy Star Clusters in NGC 1023 as Remnants of Merged Star Cluster Complexes

  R C Brüns, P Kroupa, M Fellhauer
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  ABSTRACT: In the lenticular galaxy NGC 1023 a third population of globular clusters (GCs), called faint fuzzies (FFs), was discovered next to the blue and red GC populations by Larsen & Brodie. While these FFs have colors comparable to the red population, the new population is fainter, larger (R eff > 7 pc) and, most importantly, shows clear signs of co-rotation with the galactic disk of NGC 1023. We present N-body simulations verifying the hypothesis that these disk-associated FFs are related to the young massive cluster complexes (CCs) observed by Bastian et. al in M51, who discovered a mass-radius relation for these CCs. Our models have an initial configuration based on the observations from M51 and are placed on various orbits in a galactic potential derived for NGC 1023. All computations end up with a stable object containing 10 to 60% of the initial CC mass after an integration time of 5 Gyr. A conversion to visual magnitudes demonstrates that the resulting objects cover exactly the observed range for FFs. Moreover, the simulated objects show projected half-mass radii between 3.6 and 13.4 pc, in good agreement with the observed FF sizes. We conclude that objects like the young massive CCs in M51 are likely progenitors of the FFs observed in NGC 1023.
  08/2009;