The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
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DOI：
10.1093/mnras/stab2696
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发表时间：
2021-03
影响因子：
4.8
通讯作者：
G. Becker;Anson D’Aloisio;H. Christenson;Yong Zhu;G. Worseck;J. Bolton
中科院分区：
文献类型：
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作者：
G. Becker;Anson D’Aloisio;H. Christenson;Yong Zhu;G. Worseck;J. Bolton
电离光子的平均自由程 λmfp 是星际介质 (IGM) 光电离的关键因素。然而，在 z ≳ 5 时，λmfp 可能足够短，以致 QSO 的测量会因 QSO 邻近效应而产生偏差。我们提出了新的 λmfp 直接测量方法，解决了这种偏差，并首次扩展到 z ∼ 6。我们在 z ∼ 5 处的测量基于巨型双子座 GMOS 调查和新的凯克 LRIS 对低光度 QSO 的观测数据。在 z ∼ 6 处，我们使用 Keck ESI 和 VLT X-Shooter 的 QSO 谱。我们分别在 z = 5.1 和 6.0 处测量 $\lambda _{\rm mfp} = 9.09^{+1.62}_{-1.28}$ 正确 Mpc 和 $0.75^{+0.65}_{-0.45}$ 正确 Mpc（68% 置信度）。 z = 5.1 处的结果与现有测量结果一致，表明在该红移处邻近效应造成的偏差很小。然而，在 z = 6.0 时，我们发现忽略邻近效应会使结果偏差高两倍或更多。我们在 z = 6.0 处的测量值远低于较低红移的推断，表明 λmfp 在 5 < z < 6 范围内快速演变。这种演变不利于再电离结束得足够早，以至于 IGM 有时间在 z = 6 时完全放松流体动力学的模型，但与在 z = 6 甚至更晚完成再电离的模型定性一致。我们的平均自由程结果与后期再电离模型最为一致，其中 IGM 在 z = 6 时仍为 20% 中性，尽管我们在 z = 6.0 时的测量值甚至低于这些模型偏好的值。
The mean free path of ionizing photons, λmfp, is a key factor in the photoionization of the intergalactic medium (IGM). At z ≳ 5, however, λmfp may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of λmfp that address this bias and extend up to z ∼ 6 for the first time. Our measurements at z ∼ 5 are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At z ∼ 6 we use QSO spectra from Keck ESI and VLT X-Shooter. We measure $\lambda _{\rm mfp} = 9.09^{+1.62}_{-1.28}$ proper Mpc and $0.75^{+0.65}_{-0.45}$ proper Mpc (68 per cent confidence) at z = 5.1 and 6.0, respectively. The results at z = 5.1 are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At z = 6.0, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at z = 6.0 falls well below extrapolations from lower redshifts, indicating rapid evolution in λmfp over 5 < z < 6. This evolution disfavours models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by z = 6, but is qualitatively consistent with models wherein reionization completed at z = 6 or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20 per cent neutral at z = 6, although our measurement at z = 6.0 is even lower than these models prefer.