科研之友
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摘要
We model and analyse the secular evolution of stellar bars in spinning dark matter (DM) haloes with the cosmological spin lambda similar to 0-0.09. Using high-resolution stellar and DM numerical simulations, we focus on angular momentum exchange between stellar discs and DM haloes of various axisymmetric shapes -spherical, oblate, and prolate. We find that stellar bars experience a diverse evolution that is guided by the ability of parent haloes to absorb angular momentum, J, lost by the disc through the action of gravitational torques, resonant and nonresonant. We confirm that dynamical bar instability is accelerated via resonant J-transfer to the halo. Our main findings relate to the long-term secular evolution of disc-halo systems: with an increasing lambda, bars experience less growth and basically dissolve after they pass through vertical buckling instability. Specifically, with increasing lambda, (1) the vertical buckling instability in stellar bars colludes with inability of the inner halo to absorb J-this emerges as the main factor weakening or destroying bars in spinning haloes; (2) bars lose progressively less J, and their pattern speeds level off; (3) bars are smaller, and for lambda greater than or similar to 0.06 cease their growth completely following buckling; (4) bars in lambda > 0.03 haloes have ratio of corotation-to-bar radii, R-CR/R-b > 2, and represent so-called slow bars without offset dust lanes. We provide a quantitative analysis of J-transfer in disc-halo systems, and explain the reasons for absence of growth in fast spinning haloes and its observational corollaries. We conclude that stellar bar evolution is substantially more complex than anticipated, and bars are not as resilient as has been considered so far.
- 出版日期2018-5
