EIGER. VIII. First stars signatures in the connection between O I absorption and galaxies in the epoch of reionization

article EIGER. VIII. First stars signatures in the connection between O I absorption and galaxies in the epoch of reionization published yes Jack Higginson author Rongmon Bordoloi author Robert A. Simcoe author Jorryt J Matthee author 7439a258-f3c0-11ec-9501-9df22fe067200000-0003-2871-127X Daichi Kashino author Ruari Mackenzie author Ivan Kramarenko author 9a9394cb-3200-11ee-973b-f5ba2a8b16e40000-0001-5346-6048 Simon J. Lilly author Anna-Christina Eilers author Rohan P. Naidu author Minghao Yue author JoMa department GradSch department Young galaxies as tracers and agents of cosmic reionization project We investigate the association between galaxies and neutral O I absorption systems at z ∼ 6, which trace metalenriched gas during the epoch of reionization. We identify 40 galaxies across six quasar fields, residing in 15 overdensities within 300 kpc of the background sight lines. Five O I absorption systems are associated with five of these overdensities, yielding a covering fraction of 0.27 0.10 +0.13 within 300 kpc. The absorption occurs beyond typical virial radii, indicating that the gas traces extended overdensity environments rather than individual galaxy halos, unlike the z ∼ 0 circumgalactic medium (CGM), which is largely bound to halos. These galaxy-associated absorbers account for ∼35% of all O I systems seen in blind quasar surveys, implying the remainder arise in lower-mass galaxies below our detection threshold or in dense neutral intergalactic medium pockets. The CGM around these galaxies contains ≳ 2 × 106 M⊙ of oxygen, comparable to the interstellar medium oxygen mass of the galaxies themselves, suggesting that the surrounding environment holds as much metal mass as the galaxies. All five galaxy-associated systems show significantly higher log NCII NOI ( / ) ratios than absorbers lacking galaxy associations. Furthermore, relative abundance ratios ([Si/O], [C/O]) reveal that four of the five exhibit enrichment patterns consistent with Population III nucleosynthesis at the outskirts of galaxy overdensities. These rare systems offer a unique window into the role of first-generation stars in shaping the early metal enrichment of galaxies and their environments. https://research-explorer.ista.ac.at/download/23115/23136/2026_AstrophysicalJour_Higginson.pdf application/pdfno IOP Publishing2026 eng The Astrophysical Journal 0004-637X 1538-4357 2510.0522010.3847/1538-4357/ae3e81 9991 Higginson, Jack, Rongmon Bordoloi, Robert A. Simcoe, Jorryt J Matthee, Daichi Kashino, Ruari Mackenzie, Ivan Kramarenko, et al. “EIGER. VIII. First Stars Signatures in the Connection between O I Absorption and Galaxies in the Epoch of Reionization.” The Astrophysical Journal. IOP Publishing, 2026. <a href="https://doi.org/10.3847/1538-4357/ae3e81">https://doi.org/10.3847/1538-4357/ae3e81</a>. Higginson J, Bordoloi R, Simcoe RA, et al. EIGER. VIII. First stars signatures in the connection between O I absorption and galaxies in the epoch of reionization. The Astrophysical Journal. 2026;999(1). doi:<a href="https://doi.org/10.3847/1538-4357/ae3e81">10.3847/1538-4357/ae3e81</a> J. Higginson et al., “EIGER. VIII. First stars signatures in the connection between O I absorption and galaxies in the epoch of reionization,” The Astrophysical Journal, vol. 999, no. 1. IOP Publishing, 2026. Higginson J, Bordoloi R, Simcoe RA, Matthee JJ, Kashino D, Mackenzie R, Kramarenko I, Lilly SJ, Eilers A-C, Naidu RP, Yue M. 2026. EIGER. VIII. First stars signatures in the connection between O I absorption and galaxies in the epoch of reionization. The Astrophysical Journal. 999(1), 49. J. Higginson, R. Bordoloi, R.A. Simcoe, J.J. Matthee, D. Kashino, R. Mackenzie, I. Kramarenko, S.J. Lilly, A.-C. Eilers, R.P. Naidu, M. Yue, The Astrophysical Journal 999 (2026). Higginson, Jack, et al. “EIGER. VIII. First Stars Signatures in the Connection between O I Absorption and Galaxies in the Epoch of Reionization.” The Astrophysical Journal, vol. 999, no. 1, 49, IOP Publishing, 2026, doi:<a href="https://doi.org/10.3847/1538-4357/ae3e81">10.3847/1538-4357/ae3e81</a>. Higginson, J., Bordoloi, R., Simcoe, R. A., Matthee, J. J., Kashino, D., Mackenzie, R., … Yue, M. (2026). EIGER. VIII. First stars signatures in the connection between O I absorption and galaxies in the epoch of reionization. The Astrophysical Journal. IOP Publishing. <a href="https://doi.org/10.3847/1538-4357/ae3e81">https://doi.org/10.3847/1538-4357/ae3e81</a> 231152026-10-12T12:15:27Z2026-10-14T07:58:57Z