“Changing-look” active galactic nuclei (CL-AGNs) challenge our basic ideas about the physics of accretion flows and circumnuclear gas around supermassive black holes. Using first-year Sloan Digital Sky Survey V (SDSS-V) repeated spectroscopy of nearly 29,000 previously known active galactic nuclei (AGNs), combined with dedicated follow-up spectroscopy, and publicly available optical light curves, we have identified 116 CL-AGNs where (at least) one broad emission line has essentially (dis-)appeared, as well as 88 other extremely variable systems. Our CL-AGN sample, with 107 newly identified cases, is the largest reported to date, and includes ∼0.4% of the AGNs reobserved in first-year SDSS-V operations. Among our CL-AGNs, 67% exhibit dimming while 33% exhibit brightening. Our sample probes extreme AGN spectral variability on months to decades timescales, including some cases of recurring transitions on surprisingly short timescales (≲2 months in the rest frame). We find that CL events are preferentially found in lower-Eddington-ratio (f _Edd) systems: Our CL-AGNs have a f _Edd distribution that significantly differs from that of a carefully constructed, redshift- and luminosity-matched control sample (Anderson–Darling test yielding p _AD ≈ 6 × 10⁻⁵; median f _Edd ≈ 0.025 versus 0.043). This preference for low f _Edd strengthens previous findings of higher CL-AGN incidence at lower f _Edd, found in smaller samples. Finally, we show that the broad Mg ii emission line in our CL-AGN sample tends to vary significantly less than the broad Hβ emission line. Our large CL-AGN sample demonstrates the advantages and challenges in using multi-epoch spectroscopy from large surveys to study extreme AGN variability and physics.

中文翻译：

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利用斯隆数字巡天 V 探索不断变化的活动星系核：第一年结果

“变化外观”的活动星系核（CL-AGN）挑战了我们关于超大质量黑洞周围吸积流和核周气体物理学的基本观念。利用第一年的斯隆数字巡天 V (SDSS-V) 对近 29,000 个先前已知的活动星系核 (AGN) 进行的重复光谱分析，结合专用的后续光谱分析和公开的光学光变曲线，我们已经识别出 116 个 CL-AGN其中（至少）一条广泛的发射线以及 88 个其他极其可变的系统基本上（消失）出现了。我们的 CL-AGN 样本包含 107 个新发现的病例，是迄今为止报告的最大样本，其中包括在第一年 SDSS-V 操作中重新观察到的 AGN 的约 0.4%。在我们的 CL-AGN 中，67% 表现出变暗，而 33% 表现出变亮。我们的样本探测了几个月到几十年时间尺度上的极端活动星系核光谱变异性，包括一些在令人惊讶的短时间尺度上（在其余框架中≲2个月）重复出现转变的情况。我们发现 CL 事件优先出现在较低的爱丁顿比率中（F _Edd ) 系统：我们的 CL-AGN 有F _Edd分布与精心构造的、红移和光度匹配的对照样本显着不同（Anderson-Darling 测试得出p _AD ≈ 6 × 10 ^-5；中位数F _Edd ≈ 0.025 与 0.043）。这种对低的偏好F _Edd强化了之前的发现，即在较低的条件下 CL-AGN 发生率较高。F _Edd，在较小的样本中发现。最后，我们表明广泛的 Mg二、我们的 CL-AGN 样本中的发射线的变化往往显着小于宽 Hβ发射线。我们的大型 CL-AGN 样本展示了使用大型调查的多历元光谱来研究极端 AGN 变化和物理的优势和挑战。