Sinking Satellites and Tilting Disk Galaxies

The infall of a satellite galaxy onto a galactic disk generally brings inangular momentum that is not aligned with the axis of the disk. The maindynamical issues addressed are what fraction of the orbital angular momentum ofthe satellite and the associated energy is added to the disk, as opposed tobeing left in the halo, and whether the absorbed fraction is added coherentlyor thermalized in the disk. By employing fully self-consistentdisk+halo+satellite N-body simulations, we study the particular case of thesatellite and main halo having similar density profiles, with internalvelocities having the ``cosmological'' scaling $\sigma\propto M^{1/3}$. We findthat most of the orbital angular momentum of the infalling satellite is left inthe tidally stripped satellite remnants, with only $2\%$, $6\%$ and $9\%$ ofthe orbital angular momentum being transferred to disks and halos for $10\%$,$20\%$ and $30\%$ disk-mass satellites respectively. Because the disks aretilted by the infall of $10\%$, $20\%$ and $30\%$ disk-mass satellites byangles of $(2.9\pm0.3)^\circ$, $(6.3\pm0.1)^\circ$ and $(9.7\pm0.2)^\circ$respectively, the kinetic energy associated with the vertical motion in theinitial coordinate frame of the three disks is respectively increased by$(6\pm3)\%$, $(26\pm3)\%$ and $(51\pm5)\%$ whereas the corresponding diskthermal energy associated with the vertical random motion in the tiltedcoordinate frame is only increased by $(4\pm3)\%$, $(6\pm2)\%$ and$(10\pm2)\%$, respectively. Under our initial conditions, a satellite having upto 20\% of the disk mass would produce little observable thickening whereas a30\% disk-mass satellite produces little observable thickening inside thehalf-mass radius of the disk but great damage beyond the half-mass radius.