Radial Heating of a Galactic Disk by Multiple Spiral Density Waves

Details Radial Heating of a Galactic Disk by Multiple Spiral Density Waves Radial Heating of a Galactic Disk by Multiple Spiral Density Waves

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dda....37.0603m&link_type=abstract

American Astronomical Society, DDA meeting #37, #06.03; Bulletin of the American Astronomical Society, Vol. 38, p.669

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We consider a differentially rotating, 2D stellar disk perturbed by two steady state spiral density waves moving at different pattern speeds. Our investigation is based on direct numerical integration of initially circular test-particle orbits. We examine a range of spiral strengths and spiral speeds and show that stars in this time dependent gravitational field can be heated (their random motions increased). This is particularly noticeable in the simultaneous propagation of a two-armed spiral density wave near the corotation resonance (CR), and a weak four-armed one near the inner and outer 4:1 Lindblad resonances. In simulations with two spiral waves moving at different pattern speeds we find: (1) the variance of the radial velocity, (σR)2, exceeds the sum of the variances measured from simulations with each individual pattern; (2) (σR)2 can grow with time throughout the entire simulation; (3) (σR)2 is increased over a wider range of radii compared to that seen with one spiral pattern; (4) particles diffuse radially in real space whereas they don't when only one spiral density wave is present. Near the CR with the stronger, two-armed pattern, test particles are observed to migrate radially. These effects take place at or near resonances of both spirals so we interpret them as the result of stochastic motions. This provides a possible new mechanism for increasing the stellar velocity dispersion in galactic disks. If multiple spiral patterns are present in the Galaxy we predict that there should be large variations in the stellar velocity dispersion as a function of radius.

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