The Galactic Warp and Outer Spiral Pattern: Caused by the Magellanic Clouds?

Previous abstract Next abstract

Session 22 -- Galactic Structure; Galactic Center
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[22.09] The Galactic Warp and Outer Spiral Pattern: Caused by the Magellanic Clouds?

Jeremy C. Hallum (Mankato State U.), Gene G. Byrd (University of Alabama, Tuscaloosa)

The warp of our galaxy was discovered by Kerr (1957) and has since been found at many wavelengths such as CO (Wouterloot et al 1990), young stars (Stenholm 1975) and 1.25 microns (Freudenreich 1994). Explanations for the warp started with the hypothesis of tidal creation by the Magellanic Clouds by Hunter and Toomre (1969) who found that a close approach of 20 kpc by the Magellanic clouds was required. Simulations by Spight and Grayzeck (1978) confirmed the 20 kpc close approach distance. The discovery of the Magellanic Stream (Mathewson et al 1974) and simulation studies of its creation via a tidal encounter with our galaxy (e.g. Fujimoto and Murai 1984, Lin 1993) indicate that the Clouds are near their perigalactic point at their present distance of 52 kpc (not 20 kpc!). The general conclusion is that ``It is unlikely that the tidal pull of the Magellanic Clouds is responsible for the warp (Sparke 1993)."

Since new measurements have been made of the proper motion of the Clouds (Jones et al 1994, Lin 1993) which improve our knowledge of the Clouds' orbit and since the 1978 study of tidal warping by Spight and Grayzeck was done when the extent and mass of dark matter halos of galaxies were not fully appreciated, we have conducted new simulations of the tidal effect of the Magellanic Clouds on the disk of our galaxy. These simulations were required to be consistent with the Clouds' observational parameters and included gravitational drag by an extended halo of our galaxy. First we integrated the Magellanic Clouds backward in time then we inserted a disk of massless particles in our galaxy and integrated the system forward to the present. We used different masses and other observed parameters for the Clouds consistent with observational errors. In this poster, we display the resulting warp and arm patterns and compare them to recent observations.

This work was supported by NSF grants REU AST 9300413, EPSCoR RII8996152 and AST 9014137.

Monday program listing