Galactic Warps in Triaxial Halos

Abstract

We study the behaviors of galactic disks in triaxial halos both numerically and analytically to see if warps can be excited and sustained in triaxial potentials. We consider the following two scenarios: 1) galactic disks that are initially tilted relative to the equatorial plane of the halo (for a pedagogical purpose), and 2) tilted infall of dark matter relative to the equatorial plane of the disk and the halo. With numerical simulations of 100,000 disk particles in a fixed halo potential, we find that in triaxial halos, warps can be excited and sustained just as in spherical or axisymmetric halos but they show some oscillatory behaviors and even can be transformed to a polar-ring system if the halo has a prolate-like triaxiality. The non-axisymmetric component of the halo causes the disk to nutate, and the differential nutation between the inner and outer parts of the disk generally makes the magnitude of the warp slightly diminish and fluctuate. We also find that warps are relatively weaker in oblate and oblate-like triaxial halos, and since these halos are the halo configurations of disk galaxies inferred by cosmological simulations, our results are consistent with the fact that most of the observed warps are quite weak. We derive approximate formulae for the torques exerted on the disk by the triaxial halo and the dark matter torus, and with these formulae we successfully describe the behaviors of the disks in our simulations. The techniques used in deriving these formulae could be applied for realistic halos with more complex structures.

Accepted for publication in ApJ

References in corpus (7)

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• The spin and shape of dark matter haloes in the Millennium simulation of a LambdaCDM universe
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• Internal Alignment of the Halos of Disk Galaxies in Cosmological Hydrodynamic Simulations
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• SDSS J092609.45+334304.1: a nearby unevolved galaxy
• A Case against a Significant Detection of Precession in the Galactic Warp
• A slightly oblate dark matter halo revealed by a retrograde precessing Galactic disk warp
• Modelling the shapes of the largest gravitationally bound objects
• Evidence for Populations-dependent vertical motions and the Long-lived Non-Steady Lopsided Milky Way Warp
• Warped Disk Galaxies. I. Linking U type Warps in Groups/Clusters to Jellyfish Galaxies
• RR Lyrae stars trace the Milky Way warp
• Dynamics of galactic disks in the nonaxisymmetric dark halo
• Satellite Infall and Mass Deposition on the Galactic Centre