Star cluster complexes in quiescent, active and interacting galaxies
Zusammenfassung der Projektergebnisse
Globular star clusters are among the oldest radiant objects in the universe. They were formed at the same time as the very first galaxies during the cosmological epoch of structure formation. Recendy, unusually extended globular clusters (ECs) with a relatively low surface brightness became observable in detail. Two types of ECs were found: ECs located at large distances within galactic halos and ECs associated wilh galactic disks. The ECs associated with the galactic disk were called faint fuzzies (FFs) by Larsen & Brodie (2000). The rapidly increasing number of detected objects, which are associated with various types of galaxies in differeni environments, allows for the first time an indepth investigation of their nature. In addition, recent observations of massively interacting galaxies have shown that young massive star cluster complexes (CCs) can reach masses up to 10^7-8 Mɵ spanning many hundred pc in extent and containing dozens and possibly hundreds of young massive star clusters. Since galaxy-galaxy mergers are anticipated to have been more common during early cosmological structure formation it is expected that star formation in CCs has been a significant star formation mode then. An important question about these CCs concerns their future evolution. Kroupa (1998) studied the dynamical evolution of CCs observed to be forming in the interacting Antennae galaxies and showed that in CCs of high star cluster density, significant merging of star clusters is likely. In the first part of the project we studied the evolution of CCs in the disk of galaxies which could be the progenitors of FFs. We focused on the nearby lenticular galaxy NGC 1023 where comprehensive observational data on FFs were available from Larsen & Brodie (2000). The initial conditions for the CC models in our simulalions were constrained by the mass-radius relation from Bastian el al. (2005). The simulations demonstrate that CCs from the high-mass end of the Bastian relation evolve into FF-like objects. The simulated merger objects resemble the observed parameters mass/luminosity, size and spatial distribution of FFs in NGC 1023 very well. The merging of young massive CCs is therefore a likely formation scenario for FFs. In the second part of the project we investigated the future fate of CCs in low gravitational field environments. The Milky Way EC NGC 2419 is one of the most luminous, one of the most distant, and as well one of the most extended globular clusters of the Milky Way and has been observationally studied in great detail. We proposed 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 young Milky Way. We performed a parametric study of CCs moving on a highly eccentric orbit in the Galactic halo. We varied 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 majorily of star clusters merged into a stable object. The derived parameters mass, absolute V-band magnitude, effective radius, velocity dispersion and the surface brightness profile are, for a number of models, in good agreement with those observed for NGC 2419. We showed that NGC 2419 can be well explained by the merged cluster complex scenario.
Projektbezogene Publikationen (Auswahl)
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2009, ApJ, 702, 1268 . Faint Fuzzy Star Clusters in NGC 1023 as Remnants of Merged Star Cluster Complexes
Bruns, R. C , Kroupa, P., & Fellhauer, M.
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2011, ApJ, 729, 69. A New Formation Scenario for the Milky Way Cluster NGC 2419
Bruns, R. C., & Kroupa, P.
