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
arXiv (Cornell University)(2022)
Abstract
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.
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Key words
photon escape,outflow promoting ionizing
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