Composite Quasar Spectra from the Sloan Digital Sky Survey
Composite Quasar Spectra from the Sloan Digital Sky Survey
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DOI：
10.1086/321167
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发表时间：
2001-05
期刊：
影响因子：
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通讯作者：
S. C. D. E. V. Berk;E. al.
中科院分区：
文献类型：
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作者：
S. C. D. E. V. Berk;E. al.
我们已经创建了各种复合类星体光谱使用均匀的数据集超过2200光谱从斯隆数字巡天（SDSS）。类星体样本的红移范围为0.044 ≤ z ≤ 4.789，绝对r'星等范围为-18.0至-26.5。输入光谱覆盖在分辨率为1800的3800-9200 A的观测波长范围。中值复合物覆盖从800至8555 A的静止波长范围，并且在静止帧中达到每1 A分辨率元素超过300的峰值信噪比。我们已经确定了光谱中的80多个发射线特征。相对于标称实验室波长的发射线位移被认为是许多离子物种。如前所述，宽允许和半禁线的峰位移与电离能密切相关，但我们发现窄禁线也与电离能密切相关。禁止线的位移幅度为100 km s-1，而某些允许线和半禁止线的位移高达550 km s-1。在比Lyα发射更长的波长处，几何平均复合的连续谱很好地符合两个幂律，在λ 5000 A处有一个突变。频率幂律指数αν在1300 ~ 5000 A范围内为-0.44，在1300 ~ 5000 A范围内为-2.45。斜率的突然变化可以部分地由低红移的宿主星系污染来解释。恒星的吸收线，包括高阶的巴耳末线，在合成物中显示，年轻或中等年龄的恒星对宿主星系的光做出了重大贡献。大部分的光谱都是由混合发射线组成的，特别是在1500-3500 A的范围内，这使得类星体连续体的估计非常不确定，除非观察到大范围的波长。一个中等类星体模板的电子表格是可用的。
We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ≤ z ≤ 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800–9200 A at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 A and reaches a peak signal-to-noise ratio of over 300 per 1 A resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is 100 km s-1, compared with shifts of up to 550 km s-1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lyα emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at ≈5000 A. The frequency power-law index, αν, is -0.44 from ≈1300 to 5000 A and -2.45 redward of ≈5000 A. The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500–3500 A, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.