EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich
Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z
Primordial Galaxies?
We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with
low metallicities (0.016β0.098Β Zββ) and low stellar masses
(104.7β107.6Mββ). Taking deep medium-high resolution
(RβΌ7500) integral-field spectra with 8.2-m Subaru, we resolve the small
inner velocity gradients and dispersions of the EMPGs with HΞ± emission.
Carefully masking out sub-structures originated by inflow and/or outflow, we
fit 3-dimensional disk models to the observed HΞ± flux, velocity, and
velocity-dispersion maps. All the EMPGs show rotational velocities (vrotβ) of 5--23 km sβ1 smaller than the velocity dispersions
(Ο0β) of 17--31 km sβ1, indicating dispersion-dominated (vrotβ/Ο0β=0.29β0.80<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 fgasββ0.9β1.0. Comparing our results with
other HΞ± kinematics studies, we find that vrotβ/Ο0β
decreases and fgasβ increases with decreasing metallicity, decreasing
stellar mass, and increasing specific star-formation rate. We also find that
simulated high-z (zβΌ7) 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 zβΌ7.Comment: Submitted to ApJ; After revisio