Intrinsic alignments of galaxies in the EAGLE and cosmo-OWLS simulations

Velliscig, M.; Cacciato, M.; Schaye, J.; Hoekstra, H.; Bower, R.G.; Crain, R.A.; van Daalen, M.P.; Furlong, M.; McCarthy, I.G.; Schaller, M.; Theuns, T.

Abstract

We report results for the alignments of galaxies in the EAGLE and cosmo-OWLS hydrodynamical cosmological simulations as a function of galaxy separation (−1 ≤ log10(r/[ h−1 Mpc]) ≤ 2) and halo mass (10.7 ≤ log10(M200/[h−1 M⊙]) ≤ 15). We focus on two classes of alignments: the orientations of galaxies with respect to either the directions to, or the orientations of, surrounding galaxies. We find that the strength of the alignment is a strongly decreasing function of the distance between galaxies. For galaxies hosted by the most massive haloes in our simulations the alignment can remain significant up to ∼100 Mpc. Galaxies hosted by more massive haloes show stronger alignment. At a fixed halo mass, more aspherical or prolate galaxies exhibit stronger alignments. The spatial distribution of satellites is anisotropic and significantly aligned with the major axis of the main host halo. The major axes of satellite galaxies, when all stars are considered, are preferentially aligned towards the centre of the main host halo. The predicted projected direction–orientation alignment, ϵg+(rp), is in broad agreement with recent observations. We find that the orientation–orientation alignment is weaker than the orientation–direction alignment on all scales. Overall, the strength of galaxy alignments depends strongly on the subset of stars that are used to measure the orientations of galaxies and it is always weaker than the alignment of dark matter haloes. Thus, alignment models that use halo orientation as a direct proxy for galaxy orientation overestimate the impact of intrinsic galaxy alignments.

Citation

Velliscig, M., Cacciato, M., Schaye, J., Hoekstra, H., Bower, R., Crain, R., …Theuns, T. (2015). Intrinsic alignments of galaxies in the EAGLE and cosmo-OWLS simulations. Monthly Notices of the Royal Astronomical Society, 454(3), 3328-3340. https://doi.org/10.1093/mnras/stv2198

• Journal Article Type: Article
• Acceptance Date: Sep 21, 2015
• Publication Date: Dec 11, 2015
• Deposit Date: Feb 10, 2016
• Publicly Available Date: Feb 18, 2016
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 454
• Issue: 3
• Pages: 3328-3340
• DOI: https://doi.org/10.1093/mnras/stv2198
• Keywords: Galaxies: formation, Galaxies: haloes, Cosmology: theory, Large-scale structure of Universe.
• Public URL: https://durham-repository.worktribe.com/output/1420064