Misaligned Angular Momentum in Hydrodynamic Cosmological Simulations:
  Warps, Outer Discs, and Thick Discs
  We present a detailed analysis of a disc galaxy forming in a high-resolution
fully cosmological simulation to investigate the nature of the outer regions of
discs and their relevance for the disc formation process. Specifically, we
focus on the phenomenon of misaligned disc components and find that the outer
disc warp is a consequence of the misalignment between the inner disc and the
surrounding hot gaseous halo. As the infalling cold gas sinks toward the centre
of the galaxy, it is strongly torqued by the hot gas halo. By the time the
fresh gas reaches the central disc-forming region its angular momentum is
completely aligned with the spin of the hot gas halo. If the spin of the hot
gas halo, in turn, is not aligned with that of the inner disc, a misaligned
outer disc forms comprised of newly accreted material. The inner and outer
components are misaligned with each other because they respond differently to
infalling substructure and accretion. The warped disc feeds the main gas disc
due to viscous angular momentum losses, but small amounts of star formation in
the warp itself form a low-metallicity thick disc. We show that observations of
resolved stellar populations in warped galaxies in the local universe could
provide evidence for the presence of these processes and therefore indirectly
reveal ongoing gas accretion and the existence of hot gas halos.
