Kavli Affiliate: Masahiro Kawasaki
| First 5 Authors: Yi Xu, Masami Ouchi, Yuki Isobe, Kimihiko Nakajima, Shinobu Ozaki
| Summary:
We present demography of the dynamics and gas-mass fraction of 33 extremely
metal-poor galaxies (EMPGs) with metallicities of $0.015-0.195~Z_odot$ and low
stellar masses of $10^4-10^8~M_odot$ in the local universe. We conduct deep
optical integral-field spectroscopy (IFS) for the low-mass EMPGs with the
medium high resolution ($R=7500$) grism of the 8m-Subaru FOCAS IFU instrument
by the EMPRESS 3D survey, and investigate H$alpha$ emission of the EMPGs.
Exploiting the resolution high enough for the low-mass galaxies, we derive gas
dynamics with the H$alpha$ lines by the fitting of 3-dimensional disk models.
We obtain an average maximum rotation velocity ($v_mathrm{rot}$) of
$15pm3~mathrm{km~s^{-1}}$ and an average intrinsic velocity dispersion
($sigma_0$) of $27pm10~mathrm{km~s^{-1}}$ for 15 spatially resolved EMPGs
out of the 33 EMPGs, and find that all of the 15 EMPGs have
$v_mathrm{rot}/sigma_0<1$ suggesting dispersion dominated systems. There is a
clear decreasing trend of $v_mathrm{rot}/sigma_0$ with the decreasing stellar
mass and metallicity. We derive the gas mass fraction ($f_mathrm{gas}$) for
all of the 33 EMPGs, and find no clear dependence on stellar mass and
metallicity. These $v_mathrm{rot}/sigma_0$ and $f_mathrm{gas}$ trends should
be compared with young high-$z$ galaxies observed by the forthcoming JWST IFS
programs to understand the physical origins of the EMPGs in the local universe.
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