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 z_ spec=8.496 with log(M_ star/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]88μm and [CII]158μm 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 (≈0.5 kpc in source plane) from the JWST source. The NIRCam F444W image, including [OIII]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 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]88μm/λ5007 line ratio, and derive the electron density n_ e by photoionization modeling to be 220^+170_-100 cm^-3, which is comparable with those of z∼2-3 galaxies. We estimate an [OIII]88μm/[CII]158μm line ratio in the galaxy of >4, as high as those of known z∼6-9 galaxies. This high [OIII]88μm/[CII]158μm line ratio is generally explained by the high n_ e as well as the low metallicity (Z_ gas/Z_⊙=0.04^+0.02_-0.02), high ionization parameter (log U > -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.