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arXiv 1910.06342astro-ph.HEastro-ph.GA
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用Palomar瞬变工厂在35，000个低质量星系中寻找光学AGN变化

A search for optical AGN variability in 35,000 low-mass galaxies with the Palomar Transient Factory

Vivienne F. Baldassare, Marla Geha, Jenny Greene

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Submitted to Astrophysical Journal
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摘要：

本文分析了NASA-Sloan Atlas中$\sim50,000$附近（z<0.055）星系的长期光学变率，其中$35,000$是低质量（$M_{\ast}<10^{10}~M_{\odot}$）星系。我们使用Palomar瞬变工厂（PTF）R波段观测的差分成像来构建具有几年典型基线的光变曲线。然后，我们寻找核光输出的细微变化。我们确定是否检测到的变化是活动星系核样通过评估阻尼随机游走模型的拟合质量。我们确定了424个可变性选择的活动星系核，其中包括244个恒星质量之间的$10^{7}$和$10^{10}~M_{\odot}$。75%的低质量星系具有类似活动星系核的可变性，它们的发射线很窄，主要是恒星形成。在控制了原子核的星等之后，活动星系核的变星比例在下降到$M_{\ast}=10^{9}~M_{\odot}$时是恒定的，这表明BH的占据率在下降到这个恒星质量状态时并没有急剧下降。结合我们的NASA-Sloan Atlas样本与附近星系的样本与广泛的H $α$发射，我们发现没有依赖的变化特性与黑洞质量。然而，我们警告说，可变活动星系核的分数是强烈依赖于基线。对于少于两年的基线，整个样本的可变比例为0.25%，而对于长于两年的基线，可变比例为1.0%。最后，将Stripe 82光变曲线（Baldassare et al. 2018）与PTF光变曲线进行比较，我们发现了外观变化的AGN种群：8个星系在Stripe 82中变化，但在PTF中静止，15个星系相反。我们的PTF工作表明，在低质量星系中寻找其他选择技术错过的活动星系核的长期光学变率搜索的承诺。

英文摘要：

We present an analysis of the long-term optical variability for $\sim50,000$ nearby (z<0.055) galaxies from the NASA-Sloan Atlas, $35,000$ of which are low-mass ($M_{\ast}<10^{10}~M_{\odot}$). We use difference imaging of Palomar Transient Factory (PTF) R-band observations to construct light curves with typical baselines of several years. We then search for subtle variations in the nuclear light output. We determine whether detected variability is AGN-like by assessing the fit quality to a damped random walk model. We identify 424 variability-selected AGN, including 244 with stellar masses between $10^{7}$ and $10^{10}~M_{\odot}$. 75% of low-mass galaxies with AGN-like variability have narrow emission lines dominated by star formation. After controlling for nucleus magnitude, the fraction of variable AGN is constant down to $M_{\ast}=10^{9}~M_{\odot}$, suggesting no drastic decline in the BH occupation fraction down to this stellar mass regime. Combining our NASA-Sloan Atlas sample with samples of nearby galaxies with broad H$α$ emission, we find no dependence of variability properties with black hole mass. However, we caution that the variable AGN fraction is strongly dependent on baseline. For baselines less than two years, the variable fraction for the full sample is 0.25%, compared to 1.0% for baselines longer than two years. Finally, comparing Stripe 82 light curves (Baldassare et al. 2018) to PTF light curves, we find populations of changing-look AGN: 8 galaxies that are variable in Stripe 82, but quiescent in PTF, and 15 galaxies where the reverse is true. Our PTF work demonstrates the promise of long-term optical variability searches in low-mass galaxies for finding AGNs missed by other selection techniques.

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