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The unexpected diversity of dwarf galaxy rotation curves

Oman, KA and Navarro, JF and Fattahi, A and Frenk, CS and Sawala, T and Bower, R and Furlong, M and Schaller, M and Theuns, T and White, SDM and Crain, RA and Schaye, J (2015) The unexpected diversity of dwarf galaxy rotation curves. Monthly Notices of the Royal Astronomical Society, 452 (4). pp. 3650-3665. ISSN 0035-8711

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Abstract

We examine the circular velocity profiles of galaxies in A cold dark matter (CDM) cosmological hydrodynamical simulations from the EAGLE and LOCAL GROUPS projects and compare them with a compilation of observed rotation curves of galaxies spanning a wide range in mass. The shape of the circular velocity profiles of simulated galaxies varies systematically as a function of galaxy mass, but shows remarkably little variation at fixed maximum circular velocity. This is especially true for low-mass dark-matter-dominated systems, reflecting the expected similarity of the underlying CDM haloes. This is at odds with observed dwarf galaxies, which show a large diversity of rotation curve shapes, even at fixed maximum rotation speed. Some dwarfs have rotation curves that agree well with simulations, others do not. The latter are systems where the inferred mass enclosed in the inner regions is much lower than expected for CDM haloes and include many galaxies where previous work claims the presence of a constant density 'core'. The 'cusp versus core' issue is thus better characterized as an 'inner mass deficit' problem than as a density slope mismatch. For several galaxies, the magnitude of this inner mass deficit is well in excess of that reported in recent simulations where cores result from baryon-induced fluctuations in the gravitational potential. We conclude that one or more of the following statements must be true: (i) the dark matter is more complex than envisaged by any current model; (ii) current simulations fail to reproduce the diversity in the effects of baryons on the inner regions of dwarf galaxies; and/or (iii) the mass profiles of 'inner mass deficit' galaxies inferred from kinematic data are incorrect.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record MNRAS (October 01, 2015) 452 (4): 3650-3665. is available online at: http://dx.doi.org/10.1093/mnras/stv1504
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Date Deposited: 11 Sep 2015 13:54
Last Modified: 10 Sep 2017 06:01
DOI or Identification number: 10.1093/mnras/stv1504
URI: http://researchonline.ljmu.ac.uk/id/eprint/1981

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