The unexpected diversity of dwarf galaxy rotation curves

By K. Oman, J. Navarro, Azadeh Fattahi, Carlos S. Frenk, T. Sawala, Simon D. M. White, Richard G. Bower, Robert A. Crain, Michelle Furlong, Matthieu Schaller and 2 more. 2015

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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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/465c465fd30c744e412b1692c425f906d0bec40e

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Citations in the corpus

Small-Scale Challenges to the ΛCDM Paradigm (2017, background): “Right: Green points show the circular velocities of observed galaxies measured at 2 kpc as a function of Vmax from Oman et al. (2015) as re-created by Creasey et al. (2017).”
Small scale problems of the $\Lambda$CDM model: a short review (2016, background): “The green line, and shaded region, represent respectively the median rotation velocity, and scatter, of the galaxies simulated by [196] (from which this figure is reproduced).”
Fitting the radial acceleration relation to individual SPARC galaxies (2018, background): “This object is often considered a problematic case for ΛCDM because it has a large core extending over ∼8 kpc (e.g., Oman et al. 2015).”
FIRE in the field: Simulating the threshold of galaxy formation (2016, background): “On the more massive side, efficient density core creation should be commonplace or ubiquitous; further tests of the correlation between core properties and dark matter assembly will provide insight into the core-cusp problem and the related issue of rotation curve diversity (Oman et al. 2015).”
The APOSTLE project: Local Group kinematic mass constraints and simulation candidate selection (2015, methodology): “…(which we shall hereafter refer to as APOSTLE, a shorthand for ‘A Project Of Simulating The Local Environment’), which uses the same code developed for the EAGLE simulations (Crain et al. 2015; Schaye et al. 2015), have already been reported in Sawala et al. (2015, 2016) and Oman et al. (2015).”
The Local Group on FIRE: dwarf galaxy populations across a suite of hydrodynamic simulations (2018, background): “These high-density galaxies may represent a manifestation of the ‘diversity problem’ (Oman et al. 2015; Creasey et al. 2017) in the LG. Producing such high-density galaxies, with M∗ ∼ 108 M , may prove to be an important test of galaxy formation physics.”
One Law to Rule Them All: The Radial Acceleration Relation of Galaxies (2016, methodology): “Indeed, the same simulations were used by the same group to reach the opposite conclusion: many real galaxies show a putative “inner mass deficit” with respect to ΛCDM expectations (Oman et al. 2015).”
Understanding the shape and diversity of dwarf galaxy rotation curves in ΛCDM (2016, background): “Oman et al. (2015) compared dwarfs from recent cosmological hydrodynamic simulations with a wide array of observed dwarf galaxy rotation curves, including those from the THINGS and Little THINGS surveys (de Blok et al. 2008; Oh et al. 2011; Hunter et al. 2012; Oh et al. 2015; we refer the reader to…”
ETHOS - an effective theory of structure formation: dark matter physics as a possible explanation of the small-scale CDM problems (2015, background): “This might help to alleviate the problem of diversity of rotation curves present in dwarf galaxies as pointed by Oman et al. (2015), albeit this problem was shown clearly only at larger scales (Vmax ∼ 100kms−1) than the ones studied here.”