Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-05-24
Astronomy and Astrophysics
Astrophysics
To appear (in abridged and polished form) in New Astronomy. Three figures not included
Scientific paper
10.1016/S1384-1076(98)00025-6
We study the stability of trajectories near the disk plane of galaxy models with a triaxial dark matter halo component. We also examine the effect of weak discreteness noise, rapidly rotating bar perturbations and weak dissipation on these trajectories. If the matter distribution is triaxial and has a constant density core, dissipation leads to inflow of material inside the core radius to the centre. This leads to the formation of central masses which in turn destabilise the trajectories of any stars formed in these regions. In particular, even if the gas settles by dissipation into a flat disk, stars formed in that disk will later form a bulge like dstribution the extent of which would be related to the core radius of the halo and the original asymmetry in the plane. The process of gas inflow is regulated by the fact that too large and condensed a central mass leads to the creation of stable closed loop orbits in the central area around which the gas can move. This would appear to stop the accumulation of central mass before it becomes large enough for rapid loss of halo triaxiality. It was found that weak discreteness noise can change the fraction of such trajectories significantly and can therefore have important consequences for the modelling of galaxies. The addition of rapidly rotating bar perturbations also increases the degree of instability dramatically. So if bars can form in triaxial haloes they are likely to be quickly destroyed leaving a bulge like structure behind (which may explain the absence of bars in surveys of high redshift galaxies).
El-Zant Amr A.
Hassler Bjoern
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