The evolution of the broad-line region among SDSS quasars
The evolution of the broad-line region among SDSS quasars
复制标题
DOI：
10.1051/0004-6361:20054024
复制
发表时间：
2005-10
影响因子：
6.5
通讯作者：
T. Nagao;A. Marconi;Roberto Maiolino Arcetri Observatory;N. A. O. Japan
中科院分区：
文献类型：
--
作者：
T. Nagao;A. Marconi;Roberto Maiolino Arcetri Observatory;N. A. O. Japan
基于从 SDSS 数据版本 2 中获取的 5344 个类星体光谱，在 $2.0 \leq z \leq 4.5$ 和 $-24.5 \geq M_B \geq -29.5$ 范围内研究了各种发射线通量比对红移和类星体光度的依赖性。我们表明，与双高斯或修正洛伦兹分布相比，复合光谱中的发射线更适合幂律分布，特别是我们表明，幂律分布比其他方法更适合测量宽发射线通量。复合光谱表明，类星体光度与各种发射线通量比（例如 Nv/Civ 和 Nv/Heii）之间存在统计上显着的相关性，而类星体红移与发射线通量比之间仅存在边际相关性。我们获得详细的光电离模型来解释观察到的线比。线比与光度的相关性可以用更亮的类星体中更高的气体金属丰度来解释。对于给定的类星体光度，红移范围 $2.0 \leq z \leq 4.5$ 没有金属丰度演化。 BLR 气体云的典型金属丰度估计为 $Z \sim 5~ Z_\odot$，尽管推断的金属丰度取决于假设的 BLR 云属性，例如它们的密度分布函数和径向分布。在 $z \sim 4.5$ 之前没有金属丰度演化意味着类星体宿主星系的活跃恒星形成时期发生在 $z \ga 7$。
Based on 5344 quasar spectra taken from the SDSS Data Release 2, the dependences of various emission-line flux ratios on redshift and quasar luminosity are investigated in the ranges $2.0 \leq z \leq 4.5$ and $-24.5 \geq M_B \geq -29.5$. We show that the emission lines in the composite spectra are fitted better with power-law profiles than with double Gaussian or modified Lorentzian profiles, and in particular we show that the power-law profiles are more appropriate to measure broad emission-line fluxes than other methods. The composite spectra show that there are statistically significant correlations between quasar luminosity and various emission-line flux ratios, such as Nv/Civ and Nv/Heii, while there are only marginal correlations between quasar redshift and emission-line flux ratios. We obtain detailed photoionization models to interpret the observed line ratios. The correlation of line ratios with luminosity is interpreted in terms of higher gas metallicity in more luminous quasars. For a given quasar luminosity, there is no metallicity evolution for the redshift range $2.0 \leq z \leq 4.5$. The typical metallicity of BLR gas clouds is estimated to be $Z \sim 5~ Z_\odot$, although the inferred metallicity depends on the assumed BLR cloud properties, such as their density distribution function and their radial distribution. The absence of a metallicity evolution up to $z \sim 4.5$ implies that the active star-formation epoch of quasar host galaxies occurred at $z \ga 7$.