EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?
Submitted to ApJWe present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016−0.098Z⊙) and low stellar masses (104.7−107.6M⊙). Taking deep medium-high resolution (R∼7500) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hα emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed Hα flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities (vrot) of 5--23 km s−1 smaller than the velocity dispersions (σ0) of 17--31 km s−1, indicating dispersion-dominated (vrot/σ0=0.29−0.80<1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of fgas≃0.9−1.0. Comparing our results with other Hα kinematics studies, we find that vrot/σ0 decreases and fgas increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-z (z∼7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope (JWST) observations at z∼7