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Oscar Agertz. Profile photo.

Oscar Agertz

Associate Professor / Senior university lecturer / Wallenberg Academy Fellow

Oscar Agertz. Profile photo.

Dark matter cores all the way down


  • J. I. Read
  • O. Agertz
  • M. L M Collins

Summary, in English

We use high-resolution simulations of isolated dwarf galaxies to study the physics of dark matter cusp-core transformations at the edge of galaxy formation: M200 = 107-109 M. We work at a resolution (~4 pc minimum cell size; ~250 M per particle) at which the impact from individual supernovae explosions can be resolved, becoming insensitive to even large changes in our numerical 'sub-grid' parameters. We find that our dwarf galaxies give a remarkable match to the stellar light profile; star formation history; metallicity distribution function; and star/gas kinematics of isolated dwarf irregular galaxies. Our key result is that dark matter cores of size comparable to the stellar half-mass radius r1/2 always form if star formation proceeds for long enough. Cores fully form in less than 4 Gyr for the M200 = 108 M and ~14 Gyr for the 109 M dwarf. We provide a convenient two parameter 'coreNFW' fitting function that captures this dark matter core growth as a function of star formation time and the projected stellar half-mass radius. Our results have several implications: (i) we make a strong prediction that if Λcold dark matter is correct, then 'pristine' dark matter cusps will be found either in systems that have truncated star formation and/or at radii r > r1/2; (ii) complete core formation lowers the projected velocity dispersion at r1/2 by a factor of ~2, which is sufficient to fully explain the 'too-big-to-fail problem'; and (iii) cored dwarfs will be much more susceptible to tides, leading to a dramatic scouring of the sub-halo mass function inside galaxies and groups.

Publishing year







Monthly Notices of the Royal Astronomical Society





Document type

Journal article


Oxford University Press


  • Dark matter
  • Galaxies: dwarf
  • Galaxies: haloes
  • Galaxies: kinematics and dynamics
  • Methods: numerical




  • ISSN: 0035-8711