Self-consistent response of a galactic disc to vertical perturbations

Saha, Kanak and Jog, Chanda J (2006) Self-consistent response of a galactic disc to vertical perturbations. [Preprint]

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Abstract

We study the self-consistent, linear response of a galactic disc to vertical perturbations as induced say by a tidal interaction. We calculate the self-gravitational potential corresponding to a non-axisymmetric, self-consistent density response of the disc using the Green's function method. The response potential is shown to oppose the perturbation potential because the self-gravity of the disc resists the imposed potential, and this resistence is stronger in the inner parts of a galactic disc. For the m=1 azimuthal wavenumber, the disc response opposes the imposed perturbation upto a radius that spans a range of 4-6 disc scale-lengths, so that the disc shows a net warp only beyond this region. This physically explains the well-known but so far unexplained observation (Briggs 1990) that warps typically set in beyond this range of radii. We show that the inclusion of a dark matter halo in the calculation only marginally changes (by ~ 10 %) the radius for the onset of warps. For perturbations with higher azimuthal wavenumbers, the net signature of the vertical perturbations can only be seen at larger radii - for example beyond 7 exponential disc scale-lengths for m=10. Also, for high m cases, the magnitude of the negative disc response due to the disc self-gravity is much smaller. This is shown to result in corrugations of the mid-plane density, which explains the puzzling scalloping with m=10 detected in HI in the outermost regions ~ 30 kpc in the Galaxy by Kulkarni et al. (1982).

Item Type:	Preprint
Publication:	Monthly Notices of the Royal Astronomical Society
Publisher:	Blackwell Publishing
Keywords:	galaxies;kinematics and dynamics;galaxies;spiral; galaxies;structure
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	26 Apr 2006
Last Modified:	19 Sep 2010 04:25
URI:	http://eprints.iisc.ac.in/id/eprint/6377

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