QUEST-La Silla AGN变异性调查：通过光学变异性选择AGN候选者
The QUEST-La Silla AGN Variability Survey: selection of AGN candidates through optical variability
摘要：
我们使用来自QUEST-La Silla活动星系核（AGN）变率调查的数据，构建了$\sim 70$ deg $^2$上208，583个源的光变曲线，具有极限星等$r \sim 21$。每个光变曲线至少有40个历元，长度为$\geq 200$天。我们实现了一个随机森林算法来分类我们的对象作为活动星系核或非活动星系核根据他们的变化特征和光学颜色，不包括形态削减。我们测试了三个分类器，一个仅包括可变性特征（RF 1），一个包括可变性特征以及$r-i$和$i-z$颜色（RF 2），一个包括可变性特征以及$g-r$、$r-i$和$i-z$颜色（RF 3）。我们获得了每个分类器的高概率候选样本（hp-AGN），RF 1有5，941个候选，RF 2有5，252个候选，RF 3有4，482个候选。我们根据其$g-r$颜色划分每个样本，定义蓝色（$g-r\leq 0.6$）和红色子样本（$g-r>0.6$）。我们发现文献中已知的大多数候选者属于蓝色子样本，这并不一定令人惊讶，因为与许多文献研究不同，我们没有将样本切割为点状物体。这意味着我们可以选择那些对宿主星系的红移星光有显著贡献的活动星系核。为了测试我们的技术的效率，我们进行了光谱跟踪，确认活动星系核的性质的54个观察到的来源（81.5%的效率）中的44个。从竞选活动中，我们得出结论，RF 2提供了最纯粹的样本AGN候选人。
英文摘要：
We used data from the QUEST-La Silla Active Galactic Nuclei (AGN) variability survey to construct light curves for 208,583 sources over $\sim 70$ deg$^2$, with a a limiting magnitude $r \sim 21$. Each light curve has at least 40 epochs and a length of $\geq 200$ days. We implemented a Random Forest algorithm to classify our objects as either AGN or non-AGN according to their variability features and optical colors, excluding morphology cuts. We tested three classifiers, one that only includes variability features (RF1), one that includes variability features and also $r-i$ and $i-z$ colors (RF2), and one that includes variability features and also $g-r$, $r-i$, and $i-z$ colors (RF3). We obtained a sample of high probability candidates (hp-AGN) for each classifier, with 5,941 candidates for RF1, 5,252 candidates for RF2, and 4,482 candidates for RF3. We divided each sample according to their $g-r$ colors, defining blue ($g-r\leq 0.6$) and red sub-samples ($g-r>0.6$). We find that most of the candidates known from the literature belong to the blue sub-samples, which is not necessarily surprising given that, unlike for many literature studies, we do not cut our sample to point-like objects. This means that we can select AGN that have a significant contribution from redshifted starlight in their host galaxies. In order to test the efficiency of our technique we performed spectroscopic follow-up, confirming the AGN nature of 44 among 54 observed sources (81.5\% of efficiency). From the campaign we concluded that RF2 provides the purest sample of AGN candidates.
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