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

We present ALMA deep spectroscopy for a lensed galaxy at zspec=8.496 with log(Mstar/M⊙)∼7.8 whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in SMACS0723. Our ALMA spectrum shows [OIII]88 μm and [CII]158 μm line detections at 4.0σ and 4.5σ, respectively. The redshift and position of the [OIII] line coincide with those of the JWST source, while the [CII] line is blue-shifted by 90 km s −1 with a spatial offset of 0.′′5 kpc in source plane) from the JWST source. The NIRCam F444W image, including [OIII] λ 5007 and H β 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 whose oxygen and carbon produce the extended [OIII] λ5007 and the offset [CII] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and removals of emission spatially outside the galaxy, we evaluate the [OIII]88 μm 5007 line ratio, and derive the electron density ne by photoionization modeling to be 220+170−100 cm −3, which is comparable with those of z∼2−3 galaxies. We estimate an [OIII]88 μm/[CII]158 μm line ratio in the galaxy of >4, as high as those of known z∼6−9 galaxies. This high [OIII]88 μm/[CII]158 μm line ratio is generally explained by the high neas well as the low metallicity ( Zgas/Z⊙=0.04+0.02−0.02) high ionization parameter ( logU>−2.27), and low carbon-to-oxygen abundance ratio (log(C/O) =[−0.52:−0.24]) obtained from the JWST/NIRSpec data; further [CII] follow-up observations will constrain the covering fraction of photodissociation regions.