The Astrophysical Journal (Jan 2023)

EMPRESS. IX. Extremely Metal-poor Galaxies are Very Gas-rich Dispersion-dominated Systems: Will the James Webb Space Telescope Witness Gaseous Turbulent High-z Primordial Galaxies?

  • Yuki Isobe,
  • Masami Ouchi,
  • Kimihiko Nakajima,
  • Shinobu Ozaki,
  • Nicolas F. Bouché,
  • John H. Wise,
  • Yi Xu,
  • Eric Emsellem,
  • Haruka Kusakabe,
  • Takashi Hattori,
  • Tohru Nagao,
  • Gen Chiaki,
  • Hajime Fukushima,
  • Yuichi Harikane,
  • Kohei Hayashi,
  • Yutaka Hirai,
  • Ji Hoon Kim,
  • Michael V. Maseda,
  • Kentaro Nagamine,
  • Takatoshi Shibuya,
  • Yuma Sugahara,
  • Hidenobu Yajima,
  • Shohei Aoyama,
  • Seiji Fujimoto,
  • Keita Fukushima,
  • Shun Hatano,
  • Akio K. Inoue,
  • Tsuyoshi Ishigaki,
  • Masahiro Kawasaki,
  • Takashi Kojima,
  • Yutaka Komiyama,
  • Shuhei Koyama,
  • Yusei Koyama,
  • Chien-Hsiu Lee,
  • Akinori Matsumoto,
  • Ken Mawatari,
  • Takashi J. Moriya,
  • Kentaro Motohara,
  • Kai Murai,
  • Moka Nishigaki,
  • Masato Onodera,
  • Yoshiaki Ono,
  • Michael Rauch,
  • Tomoki Saito,
  • Rin Sasaki,
  • Akihiro Suzuki,
  • Tsutomu T. Takeuchi,
  • Hiroya Umeda,
  • Masayuki Umemura,
  • Kuria Watanabe,
  • Kiyoto Yabe,
  • Yechi Zhang

DOI
https://doi.org/10.3847/1538-4357/accc87
Journal volume & issue
Vol. 951, no. 2
p. 102

Abstract

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We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098 Z _⊙ ) and low stellar masses (10 ^4.7 –10 ^7.6 M _⊙ ). 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 H α emission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed H α flux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities ( v _rot ) of 5–23 km s ^−1 smaller than the velocity dispersions ( σ _0 ) of 17–31 km s ^−1 , indicating dispersion-dominated ( v _rot / σ _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 _gas ≃ 0.9–1.0. Comparing our results with other H α kinematics studies, we find that v _rot / σ _0 decreases and f _gas 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 observations at z ∼ 7.

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