Understanding the growth of the supermassive black holes (SMBH) powering luminous quasars, their co-evolution with host galaxies, and impact on the surrounding intergalactic medium (IGM) depends sensitively on the duration of quasar accretion episodes. Unfortunately, this time-scale, known as the quasar lifetime, tQ, is still uncertain by orders of magnitude ($t_{\rm Q} \simeq 0.01\, {\rm Myr} - 1\, {\rm Gyr}$). However, the extent of the He ii Ly α proximity zones in the absorption spectra of zqso ∼ 3–4 quasars constitutes a unique probe, providing sensitivity to lifetimes up to ∼30 Myr. Our recent analysis of 22 archival Hubble Space Telescope He ii proximity zone spectra reveals a surprisingly broad range of emission time-scales, indicating that some quasars turned on ≲1 Myr ago, whereas others have been shining for ≳30 Myr. Determining the underlying quasar lifetime distribution (QLD) from proximity zone measurements is a challenging task owing to: (1) the limited sensitivity of individual measurements; (2) random sampling of the quasar light curves; (3) density fluctuations in the quasar environment; and (4) the inhomogeneous ionization state of He ii in a reionizing IGM. We combine a seminumerical He ii reionization model, hydrodynamical simulations post-processed with ionizing radiative transfer, and a novel statistical framework to infer the QLD from an ensemble of proximity zone measurements. Assuming a lognormal QLD, we infer a mean $\langle {\rm log}_{10}(t_{\rm Q} / {\rm Myr})\rangle = 0.22^{+0.22}_{-0.25}$ and standard deviation $\sigma _{{\rm log}_{10}t_{\rm Q}} = 0.80^{+0.37}_{-0.27}$. Our results allow us to estimate the probability of detecting very young quasars with tQ ≤ 0.1 Myr from their proximity zone sizes yielding $p ({\le}0.1\, {\rm Myr}) = 0.19^{+0.11}_{-0.09}$, which is broadly consistent with recent determination at z ∼ 6.

中文翻译：

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首次测量类星体寿命分布

了解为发光类星体提供动力的超大质量黑洞 (SMBH) 的生长、它们与宿主星系的共同演化以及对周围星系间介质 (IGM) 的影响敏感地取决于类星体吸积事件的持续时间。不幸的是，这个被称为类星体寿命 tQ 的时间尺度仍然不确定数量级 ($t_{\rm Q} \simeq 0.01\, {\rm Myr} - 1\, {\rm Gyr}$ ）。然而，在 zqso ∼ 3-4 类星体的吸收光谱中，He ii Ly α 邻近区的范围构成了一个独特的探针，对高达 ∼30 Myr 的寿命提供了灵敏度。我们最近对 22 个档案哈勃太空望远镜 He ii 邻近区光谱的分析揭示了令人惊讶的广泛发射时间尺度，这表明一些类星体在 ≲1 Myr 之前开启，而其他类星体一直在 ≳30 Myr 发光。从邻近区测量中确定潜在的类星体寿命分布（QLD）是一项具有挑战性的任务，因为：（1）单个测量的灵敏度有限；(2) 类星体光变曲线的随机采样；(3) 类星体环境中的密度波动；(4) He ii 在再电离 IGM 中的不均匀电离状态。我们结合了半数值 He ii 再电离模型、经过电离辐射传输后处理的流体动力学模拟，以及一种新的统计框架，以从邻近区域测量的集合中推断 QLD。假设一个对数正态 QLD，我们推断平均 $\langle {\rm log}_{10}(t_{\rm Q} / {\rm Myr})\rangle = 0.22^{+0.22}_{-0.25}$和标准差 $\sigma _{{\rm log}_{10}t_{\rm Q}} = 0.80^{+0.37}_{-0.27}$。