Warp evidences in precessing galactic bar models
  Most galaxies have a warped shape when they are seen from an edge-on point of view. The reason for this curious form is not completely known so far and in this work we apply dynamical system tools to contribute to its explanation. Starting from a simple, but realistic, model formed by a bar and a disc, we study the effect produced by a small misalignment between the angular momentum of the system and its angular velocity. To this end, a precession model is developed and considered, assuming that the bar behaves like a rigid body. After checking that the periodic orbits inside the bar keep being the skeleton of the inner system, even after inflicting a precession to the potential, we compute the invariant manifolds of the unstable periodic orbits departing from the equilibrium points at the ends of the bar to get evidences of their warped shapes. As it is well known, the invariant manifolds associated with these periodic orbits drive the arms and rings of barred galaxies and constitute the skeleton of these building blocks. Looking at them from a side-on viewpoint, we find that these manifolds present warped shapes as those recognized in observations. Lastly, test particle simulations have been performed to determine how the stars are affected by the applied precession, confirming this way the theoretical results obtained. 
Patricia Sanchez-Martin (1,3), Merce Romero-Gomez (2), Josep J.   Masdemont (1) ((1) IEEC-UPC, Ma1, (2) ICCUB-IEEC, (3) GTM-URL)
astro-ph.GA