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Abstract: Recent observations have revealed that velocity dispersions of``ultra-compact dwarf- UCD galaxies are significantly smaller than those ofother galaxy populations in the Fornax and the Virgo clusters of galaxies. Inorder to understand the origin of the observed lower velocity dispersions ofUCDs, we numerically investigate line-of-sight velocity dispersion sigma losof galaxy populations with variously different orbits in clusters of galaxieswith the total masses of M cl. We particularly investigate radial velocitydispersion profiles sigma losR and velocity dispersions within the central200 kpc of a cluster model sigma m for galaxies with different pericenterdistances r p and orbital eccentricities e in the model with M cl = 7.0 x10^13 M sun reasonable for the Fornax cluster. We find that sigma losR andsigma m of galaxies with smaller r p are steeper and smaller, respectively, fora given initial e distribution of galaxies. For example, we find that sigma mis ~ 260 km-s for galaxies with r p <50 kpc and ~ 336 km-s for all galaxies inthe model with the mean e of 0.6. These results imply that the observed lowervelocity dispersion of UCD population is consistent with the UCDs havingsignificantly smaller r p than other galaxy populations in the Fornax. Wediscuss these results in the context of the ``galaxy threshing- scenario inwhich UCDs originate from nuclei of nucleated dwarf galaxies. We suggest thatthe observed differences in kinematical properties between UCDs and other dwarfgalaxy populations in clusters of galaxies can be understood in terms of thedifferences in orbital properties between UCDs and the dwarf populations.



Autor: Kenji Bekki

Fuente: https://arxiv.org/







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