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Title: Why do similar dwarf galaxies have such different inner rotation curves?
Plain: Two small galaxies with the same overall mass can have very different speeds of rotating gas near their centers. Cold dark matter simulations predict much more uniform behavior and dense central cusps instead of the flat cores often seen.
Precise: At fixed maximum circular velocity $V_{\mathrm{max}} = (5 \text{ to } 10)e6\,\mathrm{cm}/\mathrm{s}$, observed circular velocities at $r = 2\,\mathrm{kpc}$ vary by a factor $\sim 3$, wider than in LCDM hydrodynamic simulations, and many dwarfs show inner density slopes $\gamma = -d\operatorname{ln}(\rho)/d\operatorname{ln}(r) \sim 0$ instead of the NFW value 1. Find the mechanism: supernova-driven gas outflows, self-interacting dark matter with $\sigma/m \sim 1\,\mathrm{cm}^2/\mathrm{g}$, wave dark matter, or observational systematics (non-circular motions, pressure support). An answer reproduces the observed scatter and slope distribution in a population-level comparison.
Settled by: Simulations of a given model that reproduce the measured distribution of inner rotation curves for a complete sample, with kinematic systematics forward-modeled.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 2015