A first systematic study of [OIII] 88 μ m at z > 8 : two luminous oxygen lines and a powerful ionized outflow in the first 600 million years

We present deep ALMA Band 7 observations of the [OIII]88μm line and underlying dust continuum emission in four UV-bright, gravitationally lensed (magnification μ=1.4−3.8), JWST-selected galaxies at z=8.5−10.3, with observed magnitudes −22.5≲MUV≲−20.5. [OIII] is confidently detected in UNCOVER-10646 at z=8.5080±0.0011 ( 15σ) and DHZ1 at z=9.3113±0.0006 ( 6σ), with both being intrinsically luminous systems [ L[OIII]=(1.1−1.6)×109L⊙] that follow the local [OIII]-SFR relation. [OIII]88μm remains undetected in the two z>10 targets, including in the z=10.07 X-ray AGN UHZ1, where we obtain a deep limit of L[OIII]<6×107L⊙. Dust emission is not detected in any individual source nor in a stack ( <3σ). The high S/N [OIII]88μm detection in UNCOVER-10646 uniquely reveals an additional broad component ( FWHM=1366−329+473km/s; ∆BIC≍20) indicative of an ionized outflow. We infer a high outflow rate of Ṁout=128−46+80M⊙yr−1, corresponding to a mass loading factor η=Ṁout/SFR=2.9−1.0+1.8 that matches or exceeds theoretical predictions and JWST-based studies of ionized outflows at high redshift. While high-resolution ALMA follow-up is required to confirm and spatially resolve the outflow, this first systematic study at z>8 highlights the unique diagnostic power of [OIII]88μm in characterizing galaxies in the early Universe....