CIV线宽异常：低S/N光谱的危险
CIV Line-Width Anomalies: The Perils of Low S/N Spectra
摘要：
用大双筒望远镜获得的六个高红移类星体光谱与斯隆数字巡天以前的观测结果进行比较表明，在低信噪比数据中，不能正确识别吸收和CIV发射线轮廓的准确表征的其他问题，会严重限制基于CIV发射线的单历元质量估计的可靠性。我们结合分析这些新的高质量的数据与其他三个样品的基础上高S/N光谱的CIV发射线区域的再分析。我们发现，即使对于这个高S/N的样品，当使用FWHM来表征BLR速度色散和标准维里假设来计算质量时，仍然存在大的基于Hbeta和CIV的质量之间的分散。然而，我们证明，使用高质量的数据和线分散来表征CIV线宽，导致CIV和基于Hb的质量之间的高度一致性，在质量残差中观察到的散射<0.3 dex，估计的固有散射约为0.2 dex。
英文摘要：
Comparison of six high-redshift quasar spectra obtained with the Large Binocular Telescope with previous observations from the Sloan Digital Sky Survey shows that failure to correctly identify absorption and other problems with accurate characterization of the CIV emission line profile in low S/N data can severely limit the reliability of single-epoch mass estimates based on the CIV emission line. We combine the analysis of these new high-quality data with a reanalysis of three other samples based on high S/N spectra of the CIV emission line region. We find that a large scatter between the Hbeta- and CIV-based masses remains even for this high S/N sample when using the FWHM to characterize the BLR velocity dispersion and the standard virial assumption to calculate the mass. However, we demonstrate that using high-quality data and the line dispersion to characterize the CIV line width leads to a high level of consistency between CIV- and Hbeta-based masses, with <0.3 dex of observed scatter, and an estimated ~0.2 dex intrinsic scatter, in the mass residuals.
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