A first systematic study of [OIII] 88μm at z>8: two luminous oxygen lines and a powerful ionized outflow in the first 600 million years Algera, Hiddo S.B. Weaver, John R. Bakx, Tom J.L.C. Aravena, Manuel Bouwens, Rychard J. Cescon, Karin Chen, Chian Chou Da Cunha, Elisabete Dayal, Pratika Faisst, Andreas Ferrara, Andrea Fujimoto, Seiji Hashimoto, Takuya Heintz, Kasper Herrera-Camus, Rodrigo Hodge, Jacqueline Inami, Hanae Inoue, Akio K. Matthee, Jorryt J ; https://orcid.org/0000-0003-2871-127X Meyer, Romain Mizukoshi, Shoichiro Mondal, Chayan Nanayakkara, Themiya Oesch, Pascal A. Pallottini, Andrea Röttgering, Huub Rowland, Lucie E. Schouws, Sander Smit, Renske Sommovigo, Laura Stark, Daniel P. Sugahara, Yuma Vallini, Livia Vijarnwannaluk, Bovornpratch Van Der Werf, Paul Werner, Norbert Witstok, Joris Xiao, Mengyuan ddc:520 We present deep ALMA Band 7 observations of the [O iii] 88 µm 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. [O iii] 88 µm 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[O iii] = (1.1− 1.6) ×109 L⊙] that follow the local [O iii]-SFR relation. [O iii] 88 µm 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[O iii] < 6 × 107 L⊙. Dust emission is not detected in any individual source nor in a stack (< 3σ). The high S/N [O iii] 88 µm detection in UNCOVER-10646 uniquely reveals an additional broad component (FWHM = 1366+473 −329 km/s; ∆BIC ≈ 20) indicative of an ionized outflow. We infer a high outflow rate of M˙ out = 128+80 −46 M⊙ yr−1 , corresponding to a mass loading factor η = M˙ out/SFR = 2.9 +1.8 −1.0 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 [O iii] 88 µm in characterizing galaxies in the early Universe. Maynooth Academic Publishing 2026 info:eu-repo/semantics/article doc-type:Article Article http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/22928 Algera HSB, Weaver JR, Bakx TJLC, et al. A first systematic study of [OIII] 88μm at z&#62;8: two luminous oxygen lines and a powerful ionized outflow in the first 600 million years. <i>The Open Journal of Astrophysics</i>. 2026;9. doi:<a href="https://doi.org/10.33232/001c.165333">10.33232/001c.165333</a> eng info:eu-repo/semantics/altIdentifier/doi/10.33232/001c.165333 info:eu-repo/semantics/altIdentifier/e-issn/2565-6120 info:eu-repo/semantics/altIdentifier/arxiv/2512.14486 https://creativecommons.org/licenses/by/4.0/ info:eu-repo/semantics/openAccess