科研之友
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摘要
The broad Mg II lambda 2800 doublet has been frequently studied in connection with its potentially important role as a virial estimator of black hole mass in high-redshift quasars. An important task, therefore, is the identification of any line components that are likely related to broadening by non-virial motions. High signal-to-noise median composite spectra (binned in the "four-dimensional eigenvector 1" context of Sulentic et al.) were constructed for the brightest 680 Sloan Digital Sky Survey Data Release 7 quasars in the 0.4 <= z <= 0.75 range where both Mg II lambda 2800 and H beta are recorded in the same spectra. Composite spectra representing 90% of the quasars confirm previous findings that FWHM(Mg II lambda 2800) is about 20% narrower than FWHM(H beta). The situation is clearly different for the most extreme (Population A) sources, which are the highest Eddington radiators in the sample. In the median spectra of these sources, FWHM Mg II lambda 2800 is equal to or greater than FWHM(H beta) and shows a significant blueshift relative to H beta. We interpret the Mg II lambda 2800 blueshift as the signature of a radiation-driven wind or outflow in the highest accreting quasars. In this interpretation, the Mg II lambda 2800 line width-affected by blueshifted emission-is unsuitable for virial mass estimation in approximate to 10% of quasars.
- 出版日期2013-2-20
