Dark matter cores all the way down
Abstract
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2016
- DOI:
- 10.1093/mnras/stw713
- arXiv:
- arXiv:1508.04143
- Bibcode:
- 2016MNRAS.459.2573R
- Keywords:
-
- methods: numerical;
- galaxies: dwarf;
- galaxies: haloes;
- galaxies: kinematics and dynamics;
- dark matter;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 20 pages