The Large-Scale Orientations of Disk Galaxies

We use a 380-h-1 pc resolution hydrodynamic adaptive mesh refinement (AMR) simulation of a cosmic filament to investigate the orientations of a sample of 100 well-resolved galactic discs spanning two orders of magnitude in both stellar and halo mass. We find: (i) at z = 0, there is an almost perfect alignment at a median angle of 18°, in the inner dark matter halo regions where the discs reside, between the spin vector of the gaseous and stellar galactic discs and that of their inner host haloes. The alignment between galaxy spin and spin of the entire host halo is however significantly weaker, ranging from a median of 46° at z = 1 to 50° at z = 0. (ii) The most massive galaxy discs have spins preferentially aligned so as to point along their host filaments. (iii) The spin of discs in lower mass haloes shows, at redshifts above z 0.5 and in regions of low environmental density, a clear signature of alignment with the intermediate principal axis of the large-scale tidal field. This behaviour is consistent with predictions of linear tidal torque theory. This alignment decreases with increasing environmental density, and vanishes in the highest density regions. Non-linear effects in the high-density environments are plausibly responsible for establishing this density-alignment correlation. We expect that our numerical results provide important insights for both understanding intrinsic alignment in weak lensing from the astrophysical perspective and formation and evolution processes of galactic discs in a cosmological context. DOI: https://doi.org/10.1111/j.1365-2966.2010.16494.x Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-34419 Accepted Version Originally published at: Hahn, O; Teyssier, R; Carollo, M (2010). The large-scale orientations of disc galaxies. Monthly Notices of the Royal Astronomical Society, 405(1):274-290. DOI: https://doi.org/10.1111/j.1365-2966.2010.16494.x ar X iv :1 00 2. 19 64 v1 [ as tr oph .C O ] 9 F eb 2 01 0 Mon. Not. R. Astron. Soc. 000, 1–17 (2010) Printed 9 February 2010 (MN LTEX style file v2.2) The Large-Scale Orientations of Disk Galaxies Oliver Hahn, Romain Teyssier and C. Marcella Carollo Department of Physics, ETH Zurich, CH-8093 Zürich, Switzerland KIPAC, Stanford University, 2575 Sand Hill Road, Menlo Park, CA 94025, USA Institute for Theoretical Physics, University of Zurich, CH-8057 Zürich, Switzerland CEA Saclay, DSM/IRFU/SAP, Bâtiment 709, F-91191 Gif-sur-Yvette, Cedex, France