EDP Sciences
Free access
Volume 425, Number 1, October I 2004
Page(s) 67 - 76
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041386

A&A 425, 67-76 (2004)
DOI: 10.1051/0004-6361:20041386

Bending instabilities at the origin of persistent warps: A new constraint on dark matter halos

Y. Revaz and D. Pfenniger

Geneva Observatory, University of Geneva, 1290 Sauverny, Switzerland
    e-mail: Yves.Revaz@obs.unige.ch

(Received 29 March 2004 / Accepted 2 June 2004 )

A substantial fraction of the warps in spiral galaxies may result from bending instabilities if the disks are essentially self-gravitating. With N-body simulations, we show that galaxies with self-gravitating disks as thick as HI disks are subject to bending instabilities generating S-shaped, U-shaped or asymmetric warps. S-shaped warps persist during several rotations and keep the line of node straight. The warp amplitudes generated by bending instabilities remain however modest. Other factors must be invoked for extreme warped disks. However, bending instabilities can account for most of the cases reported in optical surveys, where the warp angle is generally less than  $5^\circ$. This mode of warping is very sensitive to the disk flattening. It also constrains the fraction of dark matter distributed in the disk and in the dark halo.

Key words: galaxies: kinematics and dynamics -- methods: N-body simulations -- cosmology: dark matter

© ESO 2004