The Sloan Digital Sky Survey Reverberation Mapping Project: How Broad Emission Line Widths Change When Luminosity Changes
The Sloan Digital Sky Survey Reverberation Mapping Project: How Broad Emission Line Widths Change When Luminosity Changes
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DOI：
10.3847/1538-4357/abb36d
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发表时间：
2020-06
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影响因子：
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通讯作者：
Shu Wang;Shu Wang;Yue Shen;Linhua Jiang;C. Grier;C. Grier;K. Horne;Y. Homayouni;B. Peterson-B.-Peter
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文献类型：
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作者：
Shu Wang;Shu Wang;Yue Shen;Linhua Jiang;C. Grier;C. Grier;K. Horne;Y. Homayouni;B. Peterson-B.-Peter
类星体的宽发射线主要由吸积连续体的光电离提供动力。中心光度的增加将增强更远云中的线发射率，导致宽线发射云的平均距离增加，平均线宽度减小，这被称为“呼吸”宽线区域。然而，不同谱线的呼吸方式不同，一些高电离谱线，例如C iv，甚至可以表现出“反呼吸”，当光度增加时，谱线变宽。使用来自斯隆数字巡天混响映射项目的多年光度和光谱监测数据，我们量化了 z ≈ 0.1–2.5 范围内统计类星体样本的广泛 Hα、Hβ、Mg ii、C iv 和 C iii] 的呼吸效应 ( )。我们发现，Hβ 显示了维里关系所预期的最一致的正常呼吸 (α ∼ -0.25)，Mg ii 和 Hα 平均显示没有呼吸 (α ∼ 0)，而 C iv (以及类似的 C iii] 和 Si iv) 主要显示反呼吸 (α > 0)。 C iv 的抗呼吸作用可以通过除了回响的广泛基础成分之外还存在不变的核心成分来很好地理解，这与早期的发现是一致的。由于内在类星体的变异性，与规范呼吸的偏差在单历元维里 BH 质量估计中引入了额外的散射（依赖于光度的偏差），这是长期以来争论的 C iv 单历元质量警告的基础。在大多数情况下，使用线色散代替 FWHM 可以减少与规范呼吸的偏差，尽管仍然很大。我们的结果加强了对混响映射的需求，以提供可靠的类星体 BH 质量，并量化基于各种线的单历元 BH 质量中变异性引起的偏差水平。
Quasar broad emission lines are largely powered by photoionization from the accretion continuum. Increased central luminosity will enhance line emissivity in more distant clouds, leading to increased average distance of the broad-line-emitting clouds and decreased averaged line width, which is known as the “breathing” broad-line region. However, different lines breathe differently, and some high-ionization lines, such as C iv, can even show “anti-breathing” where the line broadens when luminosity increases. Using multi-year photometric and spectroscopic monitoring data from the Sloan Digital Sky Survey Reverberation Mapping project, we quantify the breathing effect ( ) of broad Hα, Hβ, Mg ii, C iv, and C iii] for statistical quasar samples over z ≈ 0.1–2.5. We find that Hβ displays the most consistent normal breathing expected from the virial relation (α ∼ −0.25), Mg ii and Hα on average show no breathing (α ∼ 0), and C iv (and similarly C iii] and Si iv) mostly shows anti-breathing (α > 0). The anti-breathing of C iv can be well understood by the presence of a non-varying core component in addition to a reverberating broad-base component, which is consistent with earlier findings. The deviation from canonical breathing introduces extra scatter (a luminosity-dependent bias) in single-epoch virial BH mass estimates due to intrinsic quasar variability, which underlies the long-argued caveats of C iv single-epoch masses. Using the line dispersion instead of FWHM leads to fewer, albeit still substantial, deviations from canonical breathing in most cases. Our results strengthen the need for reverberation mapping to provide reliable quasar BH masses and to quantify the level of variability-induced bias in single-epoch BH masses based on various lines.