JWST and ALMA Multiple-line Study in and around a Galaxy at z = 8.496: Optical to Far-Infrared Line Ratios and the Onset of an Outflow Promoting Ionizing Photon Escape

Seiji Fujimoto*, Masami Ouchi, Kimihiko Nakajima, Yuichi Harikane, Yuki Isobe, Gabriel Brammer, Masamune Oguri, Clara Giménez-Arteaga, Kasper E. Heintz, Vasily Kokorev, Franz E. Bauer, Andrea Ferrara, Takashi Kojima, Claudia del P. Lagos, Sommovigo Laura, Daniel Schaerer, Kazuhiro Shimasaku, Bunyo Hatsukade, Kotaro Kohno, Fengwu SunFrancesco Valentino, Darach Watson, Yoshinobu Fudamoto, Akio K. Inoue, Jorge González-López, Anton M. Koekemoer, Kirsten Knudsen, Minju M. Lee, Georgios E. Magdis, Johan Richard, Victoria B. Strait, Yuma Sugahara, Yoichi Tamura, Sune Toft, Hideki Umehata, Gregory Walth

*Corresponding author for this work

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Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) deep spectroscopy for a lensed galaxy at zspec = 8.496 with whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in the field of SMACS J0723.3–7327. Our ALMA spectrum shows [O iii] 88 μm and [C ii] 158 μm line detections at 4.0σ and 4.5σ, respectively. The redshift and position of the [O iii] line coincide with those of the JWST source, while the [C ii] line is blueshifted by 90 km s−1 with a spatial offset of 05 (≈0.5 kpc in the source plane) from the centroid of the JWST source. The NIRCam F444W image, including [O iii] λ5007 and Hβ line emission, spatially extends beyond the stellar components by a factor of >8. This indicates that the z = 8.5 galaxy has already experienced strong outflows as traced by extended [O iii] λ5007 and offset [C ii] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and the removal of emission spatially outside the galaxy, we evaluate the [O iii] 88 μm/λ5007 line ratio, and derive the electron density ne by photoionization modeling to be cm−3, which is comparable with those of z ∼ 2–3 galaxies. We estimate an [O iii] 88 μm/[C ii] 158 μm line ratio in the galaxy of >4, as high as those of known z ∼ 6–9 galaxies. This high [O iii] 88 μm/[C ii] 158 μm line ratio is generally explained by the high ne as well as the low metallicity (), high ionization parameter (), and low carbon-to-oxygen abundance ratio (log(C/O) = [−0.52: −0.24]) obtained from the JWST/NIRSpec data; further [C ii] follow-up observations will constrain the covering fraction of photodissociation regions.
Original languageEnglish
Article number146
JournalAstrophysical Journal
Volume964
Issue number2
Number of pages21
ISSN0004-637X
DOIs
Publication statusPublished - 2024

Keywords

  • Galaxy formation
  • Galaxy evolution
  • Interstellar medium
  • Circumgalactic medium
  • Early universe
  • Reionization

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