The Time Domain Spectroscopic Survey: Changing-look Quasar Candidates from Multi-epoch Spectroscopy in SDSS-IV
The Time Domain Spectroscopic Survey: Changing-look Quasar Candidates from Multi-epoch Spectroscopy in SDSS-IV
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DOI：
10.3847/1538-4357/ac743f
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发表时间：
2022-01
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通讯作者：
P. Green;Lina Pulgarin-Duque;S. Anderson;C. MacLeod;M. Eracleous;J. Ruan;J. Runnoe;M. Graham
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作者：
P. Green;Lina Pulgarin-Duque;S. Anderson;C. MacLeod;M. Eracleous;J. Ruan;J. Runnoe;M. Graham
活动星系核（AGN）在其静止坐标系光学/紫外连续辐射中可以发生显着变化，并且在宽线辐射中具有强烈的相关变化，其时间尺度比超大质量黑洞周围吸积盘的标准模型预测的要短得多。大多数这样的变化外观或变化状态的活动星系核，以及在更高的光度下，变化外观的类星体（CLQ），都是通过对已知的类星体进行光谱跟踪发现的，这些类星体表现出很强的光度变化性。斯隆数字巡天IV（SDSS-IV）的时域光谱巡天包括对大量先前已知的类星体进行重复光谱分析，其中许多类星体是在不考虑光度变化的情况下选择的，并且光谱历元之间相隔数月至数十年。我们的视觉检查这些重复光谱的强宽线变异产生了61个新发现的CLQ候选人。我们定量地比较光谱历元来测量连续谱和H β宽线发射的变化，发现了19个CLQ，其中15个是新发现的。母样本只包括宽线类星体，所以我们的研究倾向于找到已经变暗的物体，即，关闭CLQ。然而，我们仍然找到了四个符合我们标准的开启CLQ，尽管在昏暗和明亮的状态下都有很宽的线条。我们研究了H β和Mg Ⅱ发射线对连续变化的响应。CLQ的爱丁顿比较低，和/或它们的H β宽线宽相对于整个类星体群体较大。在即将到来的SDSS-V黑洞映射程序中重复类星体光谱将揭示大量CLQ，增强我们对这种强可变性的频率和占空比以及该现象的物理和动力学的理解。
Active galactic nuclei (AGN) can vary significantly in their rest-frame optical/UV continuum emission, and with strong associated changes in broad line emission, on much shorter timescales than predicted by standard models of accretion disks around supermassive black holes. Most such changing-look or changing-state AGN—and at higher luminosities, changing-look quasars (CLQs)—have been found via spectroscopic follow-up of known quasars showing strong photometric variability. The Time Domain Spectroscopic Survey of the Sloan Digital Sky Survey IV (SDSS-IV) includes repeat spectroscopy of large numbers of previously known quasars, many selected irrespective of photometric variability, and with spectral epochs separated by months to decades. Our visual examination of these repeat spectra for strong broad line variability yielded 61 newly discovered CLQ candidates. We quantitatively compare spectral epochs to measure changes in continuum and Hβ broad line emission, finding 19 CLQs, of which 15 are newly recognized. The parent sample includes only broad line quasars, so our study tends to find objects that have dimmed, i.e., turn-off CLQs. However, we nevertheless find four turn-on CLQs that meet our criteria, albeit with broad lines in both dim and bright states. We study the response of Hβ and Mg ii emission lines to continuum changes. The Eddington ratios of CLQs are low, and/or their Hβ broad line width is large relative to the overall quasar population. Repeat quasar spectroscopy in the upcoming SDSS-V black hole Mapper program will reveal significant numbers of CLQs, enhancing our understanding of the frequency and duty cycle of such strong variability, and the physics and dynamics of the phenomenon.