Disk Structures from Triaxial Tumbling Halos
Abstract
Cosmological simulations consistently indicate that dark halos are considerably flattened, with typical axis ratios given as 2.0:1.5:1.0. Such halos are also often found to be tumbling slowly, with tumbling periods of a few gigayears. Thus, the disc that sits inside a such halo will be affected by the torque that the halo provides, as it tumbles. Such torques are responsible for driving instabilities in the disc, generating various disc structures. In this work, disc evolution is studied as a consequence of the torques that are exerted by the quadrupolar tidal field of an external, triaxial, tumbling halo, using N-body simulations of model disc galaxies. Cosmological simulations are used to constrain the amplitude of the quadrupolar term in the halo potential and the halo tumbling period; these values are subsequently used in our N-body models. Analytical calculations are also performed to gauge the strength and nature of the quadrupolar tidal field of such halos and equations of motion are tracked to predict the formation of disc features such as the central bar and the warp. As the results of these analytical calculations adumbrate, the N-body simulations indicate that the torques from the tumbling halo are potent enough to induce sustained warps in the discs. The bar instability is also noted to be induced at later times in models that would be otherwise stable in isolation. At the edge of the disk, where self-gravity is usually found in numerical models to be too weak to support spiral structure, the halo torque is noted to be strong enough to force spirality. Thus, we advance the authority of the quadrupole moment of the dark halo, in the determination of the disk structure and morphology.
- Publication:
-
Galaxy Evolution across the Hubble Time
- Pub Date:
- May 2007
- DOI:
- 10.1017/S1743921306005230
- Bibcode:
- 2007IAUS..235...86C