Journal Article

The large-scale orientations of disc galaxies

Oliver Hahn, Romain Teyssier and C. Marcella Carollo

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 405, issue 1, pages 274-290
Published in print June 2010 | ISSN: 0035-8711
Published online June 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16494.x
The large-scale orientations of disc galaxies

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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.

Keywords: methods: numerical; galaxies: evolution; galaxies: formation; cosmology: theory; large-scale structure of Universe

Journal Article.  10327 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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