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

<jats:title>Abstract</jats:title> <jats:p>We present Atacama Large Millimeter/submillimeter Array (ALMA) deep spectroscopy for a lensed galaxy at <jats:italic>z</jats:italic> <jats:sub>spec</jats:sub> = 8.496 with <jats:inline-formula> <jats:tex-math> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>star</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>∼</mml:mo> <mml:mn>7.8</mml:mn> </mml:math> </jats:inline-formula> 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 <jats:sc>iii</jats:sc>] 88 <jats:italic>μ</jats:italic>m and [C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m line detections at 4.0<jats:italic>σ</jats:italic> and 4.5<jats:italic>σ</jats:italic>, respectively. The redshift and position of the [O <jats:sc>iii</jats:sc>] line coincide with those of the JWST source, while the [C <jats:sc>ii</jats:sc>] line is blueshifted by 90 km s<jats:sup>−1</jats:sup> with a spatial offset of 0.″5 (≈0.5 kpc in the source plane) from the centroid of the JWST source. The NIRCam F444W image, including [O <jats:sc>iii</jats:sc>] <jats:italic>λ</jats:italic>5007 and H<jats:italic>β</jats:italic> line emission, spatially extends beyond the stellar components by a factor of >8. This indicates that the <jats:italic>z</jats:italic> = 8.5 galaxy has already experienced strong outflows as traced by extended [O <jats:sc>iii</jats:sc>] <jats:italic>λ</jats:italic>5007 and offset [C <jats:sc>ii</jats:sc>] 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 <jats:sc>iii</jats:sc>] 88 <jats:italic>μ</jats:italic>m/<jats:italic>λ</jats:italic>5007 line ratio, and derive the electron density <jats:italic>n</jats:italic> <jats:sub>e</jats:sub> by photoionization modeling to be <jats:inline-formula> <jats:tex-math> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>220</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>130</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>230</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> </jats:inline-formula> cm<jats:sup>−3</jats:sup>, which is comparable with those of <jats:italic>z</jats:italic> ∼ 2–3 galaxies. We estimate an [O <jats:sc>iii</jats:sc>] 88 <jats:italic>μ</jats:italic>m/[C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m line ratio in the galaxy of >4, as high as those of known <jats:italic>z</jats:italic> ∼ 6–9 galaxies. This high [O <jats:sc>iii</jats:sc>] 88 <jats:italic>μ</jats:italic>m/[C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m line ratio is generally explained by the high <jats:italic>n</jats:italic> <jats:sub>e</jats:sub> as well as the low metallicity (<jats:inline-formula> <jats:tex-math> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>Z</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>gas</mml:mi> </mml:mrow> ...