Simulations of the dynamical evolution of compact groups and poor clusters

Details Simulations of the dynamical evolution of compact groups and poor clusters Simulations of the dynamical evolution of compact groups and poor clusters

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........25b&link_type=abstract

PhD Dissertation, Indiana Univ. Indianapolis, IN United States

Mathematics

Galactic Evolution, Astronomical Models, Gravitational Fields, Galactic Clusters, Mathematical Models, Stellar Gravitation, Trees (Mathematics), Star Distribution, Galactic Nuclei

Scientific paper

The effect of dynamical evolution on clusters and their constituent galaxies is examined through simulations of compact groups and poor clusters. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the gravitational potential arises from the particles alone; the potential is found using the Barnes-Hut 'tree' algorithm. The compact group models contain five galaxies; a total of N = 5000 particles is used to represent both galaxies and a smoothly distributed intra-cluster background. The merging process is found to take longer as less of the cluster mass is put into the galaxy halos; this delay is consistent with the lengthening of the dynamical friction time scale as galaxy masses are reduced. The N = 40,000 cluster models contain 50 galaxies. Those models with half of the mass initially contained in the background all followed a similar pattern of behavior. In approximately 10 Gyr, merging has resulted in the formation of a dominant, slowly-moving, centrally located galaxy. No high peculiar-velocity brightest cluster galaxies (which are observed in approximately 10% of clusters) are produced in these models. The cluster density profile around the first-ranked galaxy (FRG) becomes strongly cusped and resembles a singular isothermal sphere; this is accompanied by an increase in the number of multiple nuclei seen in the FRG. The observed properties of poor clusters. Many observed properties of poor clusters (including Delta M12, FRG luminosity, frequency of multiple nuclei) can best be fit by cluster models with ages approximately 11 Gyr, with the exception that fitting observations of the peculiar velocities of the FRG requires younger ages of approximately 8 Gyr. Increasing the background mass fraction to 75% slows the rate of merging, but otherwise causes little change in behavior. For a fraction of 90%, the onset of merging can be delayed for over 13 Gyr; thus a dominant central galaxy is not created.

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