Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars
Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars
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DOI：
10.3847/1538-4357/ab05e2
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发表时间：
2018-09
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通讯作者：
C. MacLeod;P. Green;S. Anderson;A. Bruce;M. Eracleous;M. Graham;D. Homan;A. Lawrence;Amy Lebleu
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文献类型：
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作者：
C. MacLeod;P. Green;S. Anderson;A. Bruce;M. Eracleous;M. Graham;D. Homan;A. Lawrence;Amy Lebleu
活动星系核（AGN）在其蓝色连续谱和宽线发射中表现出强烈的静止坐标系光学/紫外变化，被归类为变貌AGN，或在更高的光度下，变貌类星体（CLQ）。这些令人惊讶的大，有时快速的转变挑战了公认的类星体物理模型和占空比，提供了几个新的途径研究类星体宿主星系，并打开了更广泛的解释之间的差异的原因宽和窄线活动星系核。为了更好地表征极端类星体的变化，我们提出了后续光谱学作为全面搜索CLQ的一部分，整个斯隆数字巡天（SDSS）的足迹使用光谱学确认的类星体从SDSS DR 7目录。我们的主要选择要求在SDSS和Pan-STARRS 1调查探测的任何可用时间基线上具有大幅度（mag，mag）变化。我们采用测光从卡塔利纳巡天，以验证在CLQ候选人的可变性行为，并确认CLQ使用光学光谱从威廉赫歇尔，MMT，麦哲伦和帕洛玛望远镜。对于我们所采用的宽Hβ发射变异性的信噪比阈值，我们发现了17个新的CLQ，确认率为20%。这些候选者是在较低的爱丁顿比相对于整个类星体的人口，这支持了广泛的线区域的盘风模型。基于我们的样品，CLQ分数从10%增加到大约一半，因为在3420 nm处重复光谱之间的连续通量比从1.5增加到6。我们发布了200多个高度可变的候选人的目录，以方便未来的CLQ搜索。
Active galactic nuclei (AGNs) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as changing-look AGN, or at higher luminosities, changing-look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow-line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full Sloan Digital Sky Survey (SDSS) footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude ( mag, mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted signal-to-noise ratio threshold on variability of broad Hβ emission, we find 17 new CLQs, yielding a confirmation rate of ≳20%. These candidates are at lower Eddington ratio relative to the overall quasar population, which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420 Å increases from 1.5 to 6. We release a catalog of more than 200 highly variable candidates to facilitate future CLQ searches.