不同视角下的射电强窄线Seyfert 1：根据光学偏振光谱法修正的黑洞质量估计
Radio-loud Narrow Line Seyfert 1 under a different perspective: a revised black hole mass estimate from optical spectropolarimetry
摘要：
一些研究表明，射电大声（RL）活动星系核（AGN）只由质量最大的黑洞（BH）产生，$M_{\rm BH} \sim 10^8$ - $10^{10} M_\odot$。这一想法受到了RL窄线Seyfert 1（RL NLSy 1）的发现的挑战，它具有估计的$M_{\rm BH}$ $\sim$ $10^6$ - $10^7$ M $_\odot$的质量.然而，这些低$M_{\rm BH}$估计值可能是由于投影效应。光谱偏振法允许我们通过在不同的视角下观察RL NLSy 1来测试这种可能性，即，从散射材料的视角。我们在这里报告的RL NLSy 1 PKS 2004-447的VLT光谱偏振观测的试点研究的结果。它的偏振特性是非常好地再现的模型中，散射发生在赤道结构周围的宽线区域，看到接近face-on.特别是，我们检测到一个偏振H $α$线的宽度为$\sim$ 9,000 km s $^{-1}$，$\sim 6$倍宽于在直射光中看到的宽度。这与修正后的$M_{\rm BH}$ $\sim$ $6\times10^8$ M $_\odot$的估计值相对应，正好在RL AGN的典型范围内。双峰极化宽H $α$配置文件的目标表明，罕见的组合的方向效应和广泛的线区域占主导地位的旋转可能占这类对象，铸造的维里估计BH质量的I型活动星系核的怀疑。
英文摘要：
Several studies indicate that radio-loud (RL) Active Galactic Nuclei (AGN) are produced only by the most massive black holes (BH), $M_{\rm BH} \sim 10^8$-$10^{10} M_\odot$. This idea has been challenged by the discovery of RL Narrow Line Seyfert 1 (RL NLSy1), having estimated masses of $M_{\rm BH}$$\sim$$10^6$-$10^7$ M$_\odot$. However, these low $M_{\rm BH}$ estimates might be due to projection effects. Spectropolarimetry allows us to test this possibility by looking at RL NLSy1s under a different perspective, i.e., from the viewing angle of the scattering material. We here report the results of a pilot study of VLT spectropolarimetric observations of the RL NLSy1 PKS 2004-447. Its polarization properties are remarkably well reproduced by models in which the scattering occurs in an equatorial structure surrounding its broad line region, seen close to face-on. In particular, we detect a polarized H$α$ line with a width of $\sim$ 9,000 km s$^{-1}$, $\sim 6$ times broader than the width seen in direct light. This corresponds to a revised estimate of $M_{\rm BH}$$\sim$$6\times10^8$ M$_\odot$, well within the typical range of RL AGN. The double-peaked polarized broad H$α$ profile of the target suggests that the rare combination of the orientation effects and a broad line region dominated by the rotation might account for this class of objects, casting doubts on the virial estimates of BH mass for type-I AGN.
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