Kavli Affiliate: Masahiro Kawasaki
| First 5 Authors: Yuki Isobe, Masami Ouchi, Kimihiko Nakajima, Shinobu Ozaki, Nicolas Bouche
| Summary:
We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with
low metallicities ($0.016-0.098 Z_{odot}$) and low stellar masses
($10^{4.7}-10^{7.6} M_{odot}$). Taking deep medium-high resolution
($Rsim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small
inner velocity gradients and dispersions of the EMPGs with H$alpha$ emission.
Carefully masking out sub-structures originated by inflow and/or outflow, we
fit 3-dimensional disk models to the observed H$alpha$ flux, velocity, and
velocity-dispersion maps. All the EMPGs show rotational velocities ($v_{rm
rot}$) of 5–23 km s$^{-1}$ smaller than the velocity dispersions
($sigma_{0}$) of 17–31 km s$^{-1}$, indicating dispersion-dominated ($v_{rm
rot}/sigma_{0}=0.29-0.80<1$) 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 $f_{rm gas}simeq 0.9-1.0$. Comparing our results with
other H$alpha$ kinematics studies, we find that $v_{rm rot}/sigma_{0}$
decreases and $f_{rm gas}$ increases with decreasing metallicity, decreasing
stellar mass, and increasing specific star-formation rate. We also find that
simulated high-$z$ ($zsim 7$) 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 $zsim 7$.
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