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Core formation in dwarf haloes with self-interacting dark matter: no fine-tuning necessary

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We investigate the effect of self-interacting dark matter (SIDM) on the density profiles of Vmax ≃ 40km s-1 isolated dwarf dark matter haloes-the scale of relevance for the too big to fail problem (TBTF)-using very high resolution cosmological zoom simulations. Each halo has millions of particles within its virial radius. We find that SIDM models with cross-sections per unitmass spanning the range s/m=0.5-50 cm2 g-1 alleviate TBTF and produce constantdensity cores of size 300-1000 pc, comparable to the half-light radii of M* ~ 105-7M⊙ dwarfs. The largest, lowest density cores develop for cross-sections in the middle of this range, σ/m ~ 5-10 cm2 g-1. Our largest SIDM cross-section run (σ/m = 50 cm2 g-1) develops a slightly denser core owing to mild core-collapse behaviour, but it remains less dense than the cold dark matter case and retains a constant-density core profile. Our work suggests that SIDM cross-sections as large or larger than 50 cm2 g-1 remain viable on velocity scales of dwarf galaxies (vrms ~ 40 km s-1). The range of SIDM cross-sections that alleviate TBTF and the cusp/core problem spans at least two orders of magnitude and therefore need not be particularly fine-tuned.

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