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

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 OIII88 μm and CII158 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 OIII88 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 OIII88 μm/CII158 μm line ratio in the galaxy of >4, as high as those of known z∼6−9 galaxies. This high OIII88 μm/CII158 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.