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Internal alignments of red versus blue discs in dark matter haloes

Debattista, Victor P. ; van den Bosch, Frank C. ; Roškar, Rok ; Quinn, Thomas ; Moore, Ben ; Cole, David R.

In: Monthly Notices of the Royal Astronomical Society, 2015, vol. 452, no. 4, p. 4094-4110

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    Title
    • Internal alignments of red versus blue discs in dark matter haloes
    Author
    • Debattista, Victor P.. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
    • van den Bosch, Frank C.. Astronomy Department, Yale University, PO Box 208101, New Haven, CT 06520-8101, USA
    • Roškar, Rok. Research Informatics, Scientific IT Services, ETH Zürich, Weinbergstrasse 11, CH-8092, Zürich, Switzerland
    • Quinn, Thomas. Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195, USA
    • Moore, Ben. Research Informatics, Scientific IT Services, ETH Zürich, Weinbergstrasse 11, CH-8092, Zürich, Switzerland
    • Cole, David R.. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Monthly Notices of the Royal Astronomical Society, 2015, vol. 452, no. 4, p. 4094-4110. Oxford University Press
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:294940
    Summary
    Large surveys have shown that red galaxies are preferentially aligned with their haloes, while blue galaxies have a more isotropic distribution. Since haloes generally align with their filaments, this introduces a bias in the measurement of the cosmic shear from weak lensing. It is therefore vitally important to understand why this difference arises. We explore the stability of different disc orientations within triaxial haloes. We show that, in the absence of gas, the disc orientation is most stable when its spin is along the minor axis of the halo. Instead when gas cools on to a disc, it is able to form in almost arbitrary orientation, including off the main planes of the halo (but avoiding an orientation perpendicular to the halo's intermediate axis). Substructure helps gasless galaxies reach alignment with the halo faster, but has less effect on galaxies when gas is cooling on to the disc. Our results provide a novel and natural interpretation for why red, gas poor galaxies are preferentially aligned with their halo, while blue, star-forming, galaxies have nearly random orientations, without requiring a connection between galaxies' current star formation rate and their merger history