Influence of baryons on the orbital structure of dark matter haloes

We explore the dynamical signatures imprinted by baryons on dark matterhaloes during the formation process using the OverWhelmingly LargeSimulations (OWLS), a set of state-of-the-art high-resolutioncosmological hydrodynamical simulations. We present a detailed study ofthe effects of the implemented feedback prescriptions on the orbits ofdark matter particles, stellar particles and subhaloes, analysing runswith no feedback, with stellar feedback and with feedback fromsupermassive black holes. We focus on the central regions(0.25r$_{200}$) of haloes with virial masses {\tilde}6 {\times}10$^{13}$ ({\tilde}7 {\times} 10$^{11}$) h$^{-1}$M$_{s}$ at z= 0 (2). We also investigate how the orbitalcontent (relative fractions of the different orbital types) of thesehaloes depends on several key parameters such as their mass, redshiftand dynamical state. The results of spectral analyses of the orbitalcontent of these simulations are compared, and the change in fraction ofbox, tube and irregular orbits is quantified. Box orbits are found todominate the orbital structure of dark matter haloes in cosmologicalsimulations. There is a strong anticorrelation between the fraction ofbox orbits and the central baryon fraction. While radiative cooling actsto reduce the fraction of box orbits, strong feedback implementationsresult in a similar orbital distribution to that of the dark matter onlycase. The orbital content described by the stellar particles is found tobe remarkably similar to that drawn from the orbits of dark matterparticles, suggesting that either they have forgotten their dynamicalhistory, or subhaloes bringing in stars are not biased significantlywith respect to the main distribution. The orbital content of thesubhaloes is in broad agreement with that seen in the outer regions ofthe particle distributions.