Evidence for coupling between the Sagittarius dwarf galaxy and the Milky Way warp

Abstract

Using recent determinations of the mass and orbit of Sagittarius, I calculate its orbital angular momentum. From the latest observational data, I also calculate the angular momentum of the Milky Way's warp. I find that both angular momenta are directed toward l=270, b=0, and have magnitude 2-8x10^12 M_Sun kpc km s^-1, where the range in both cases reflects uncertainty in the mass. The coincidence of the angular momenta is suggestive of a coupling between these systems. Direct gravitational torque of Sgr on the disk is ruled out as the coupling mechanism. Gravitational torque due to a wake in the halo and the impulsive deposition of momentum by a passage of Sgr through the disk are still both viable mechanisms pending better simulations to test their predictions on the observed Sgr-MW system.Comment: 11 pages, to appear in the February 1 issue of ApJ