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We explore the kinematic gas properties of six $5.5<z<7.4$ galaxies in theJWST Advanced Deep Extragalactic Survey (JADES), using high-resolutionJWST/NIRSpec multi-object spectroscopy of the rest-frame optical emission lines[OIII] and H$\alpha$. The objects are small and of low stellar mass ($\sim1\,$kpc; $M_*\sim10^{7-9}\,{\rm M_\odot}$), less massive than any galaxystudied kinematically at $z>1$ thus far. The cold gas masses implied by theobserved star formation rates are $\sim 10\times$ larger than the stellarmasses. We find that their ionised gas is spatially resolved by JWST, withevidence for broadened lines and spatial velocity gradients. Using a simplethin-disc model, we fit these data with a novel forward modelling software thataccounts for the complex geometry, point spread function, and pixellation ofthe NIRSpec instrument. We find the sample to include both rotation- anddispersion-dominated structures, as we detect velocity gradients of $v(r_{\rme})\approx100-150\,{\rm km\,s^{-1}}$, and find velocity dispersions of$\sigma_0\approx 30-70\,{\rm km\,s^{-1}}$ that are comparable to those atcosmic noon. The dynamical masses implied by these models ($M_{\rmdyn}\sim10^{9-10}\,{\rm M_\odot}$) are larger than the stellar masses by up toa factor 40, and larger than the total baryonic mass (gas + stars) by a factorof $\sim 3$. Qualitatively, this result is robust even if the observed velocitygradients reflect ongoing mergers rather than rotating discs. Unless theobserved emission line kinematics is dominated by outflows, this implies thatthe centres of these galaxies are dark-matter dominated or that star formationis $3\times$ less efficient, leading to higher inferred gas masses.

Ionised gas kinematics and dynamical masses of $z\gtrsim6$ galaxies from JADES/NIRSpec high-resolution spectroscopy