Missing dark matter in dwarf galaxies?

Oman, K.A.; Navarro, J.F.; Sales, L.V.; Fattahi, A.; Frenk, C.S.; Sawala, T.; Schaller, M.; White, S.D.M.

Abstract

We use cosmological hydrodynamical simulations of the APOSTLE project along with high-quality rotation curve observations to examine the fraction of baryons in ΛCDM haloes that collect into galaxies. This ‘galaxy formation efficiency’ correlates strongly and with little scatter with halo mass, dropping steadily towards dwarf galaxies. The baryonic mass of a galaxy may thus be used to place a lower limit on total halo mass and, consequently, on its asymptotic maximum circular velocity. A number of observed dwarfs seem to violate this constraint, having baryonic masses up to 10 times higher than expected from their rotation speeds, or, alternatively, rotating at only half the speed expected for their mass. Taking the data at face value, either these systems have formed galaxies with extraordinary efficiency – highly unlikely given their shallow potential wells – or their dark matter content is much lower than expected from ΛCDM haloes. This ‘missing dark matter’ is reminiscent of the inner mass deficit of galaxies with slowly rising rotation curves, but cannot be explained away by star formation-induced ‘cores’ in the dark mass profile, since the anomalous deficit applies to regions larger than the luminous galaxies themselves. We argue that explaining the structure of these galaxies would require either substantial modification of the standard ΛCDM paradigm or else significant revision to the uncertainties in their inferred mass profiles, which should be much larger than reported. Systematic errors in inclination may provide a simple resolution to what would otherwise be a rather intractable problem for the current paradigm.

Citation

Oman, K., Navarro, J., Sales, L., Fattahi, A., Frenk, C., Sawala, T., …White, S. (2016). Missing dark matter in dwarf galaxies?. Monthly Notices of the Royal Astronomical Society, 460(4), 3610-3623. https://doi.org/10.1093/mnras/stw1251

• Journal Article Type: Article
• Acceptance Date: Apr 23, 2016
• Online Publication Date: May 25, 2016
• Publication Date: Aug 21, 2016
• Deposit Date: Sep 28, 2016
• Publicly Available Date: Oct 6, 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: 460
• Issue: 4
• Pages: 3610-3623
• DOI: https://doi.org/10.1093/mnras/stw1251
• Public URL: https://durham-repository.worktribe.com/output/1373889