JWST observations have recently begun delivering the first samples of Lyα velocity profile measurements at z > 6, opening a new window into the reionization process. Interpretation of z ≳ 6 line profiles is currently stunted by limitations in our knowledge of the intrinsic Lyα profile (before encountering the intergalactic medium (IGM)) of the galaxies that are common at z ≳ 6. To overcome this shortcoming, we have obtained resolved (R ∼ 3900) Lyα spectroscopy of 42 galaxies at z = 2.1–3.4 with similar properties as are seen at z > 6. We quantify a variety of Lyα profile statistics as a function of [O iii]+Hβ equivalent width (EW). Our spectra reveal a new population of z ≃ 2–3 galaxies with large [O iii]+Hβ EWs (>1200 Å) and a large fraction of Lyα flux emerging near the systemic redshift (peak velocity ≃0 km s⁻¹). These spectra indicate that low-density neutral hydrogen channels are able to form in a subset of low-mass galaxies (≲1 × 10⁸ M _⊙) that experience a burst of star formation (sSFR > 100 Gyr⁻¹). Other extreme [O iii] emitters show weaker Lyα that is shifted to higher velocities (≃240 km s⁻¹) with little emission near the line center. We investigate the impact the IGM is likely to have on these intrinsic line profiles in the reionization era, finding that the centrally peaked Lyα emitters should be strongly attenuated at z ≳ 5. We show that these line profiles are particularly sensitive to the impact of resonant scattering from infalling IGM and can be strongly attenuated even when the IGM is highly ionized at z ≃ 5. We compare these expectations against a new database of z ≳ 6.5 galaxies with robust velocity profiles measured with JWST/NIRSpec.

中文翻译：

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z ≳ 2 处极端 [O iii] 发射星系的 Lyα 发射线剖面：对再电离时代 Lyα 可见性的影响


JWST 观测最近开始提供 z > 6 处 Lyα 速度剖面测量的第一批样本，为再电离过程打开了一个新窗口。目前，由于我们对 z ≳ 6 处常见星系的固有 Lyα 剖面（在遇到星系间介质 (IGM) 之前）的了解有限，对 z ≳ 6 线剖面的解释受到阻碍。为了克服这一缺点，我们已经解决了这一问题(R ∼ 3900) z = 2.1–3.4 处 42 个星系的 Lyα 光谱，具有与 z > 6 处相似的特性。我们将各种 Lyα 剖面统计数据量化为 [O iii]+Hβ 等效宽度 (EW ）。我们的光谱揭示了一个新的 z ≃ 2–3 星系群，具有大的 [O iii]+Hβ EW (>1200 Å) 和大部分 Lyα 通量出现在系统红移附近（峰值速度 ≃0 km s ^-1 ）。这些光谱表明，低密度中性氢通道能够在经历恒星形成爆发（sSFR > 100 Gyr ^-1 ）的低质量星系（≲1 × 10 ⁸ M _⊙ ）子集中形成。其他极端的[O iii]发射体表现出较弱的Lyα，其转移到更高的速度（≃240 km s ^-1 ），在线中心附近几乎没有发射。我们研究了再电离时代 IGM 可能对这些本征谱线轮廓产生的影响，发现中心峰值 Lyα 发射体应该在 z ≳ 5 处强烈衰减。我们表明，这些谱线轮廓对谐振的影响特别敏感来自坠落 IGM 的散射，即使当 IGM 在 z ≃ 5 处高度电离时，也会被强烈衰减。我们将这些期望与 z ≳ 6.5 星系的新数据库进行比较，并使用 JWST/NIRSpec 测量稳健的速度剖面。