Longstanding Quasar Puzzle Solved

New KIAA faculty member Yue Shen and KIAA Director Luis Ho have solved a two-decade long mystery in quasar research. Namely, what drives the diverse properties of quasars into a well-defined main sequence, known as "Eigenvector 1", where many physical quasar properties correlate with the strength of optical FeII strength. Shen and Ho used archival data from the Sloan Digital Sky Survey, combined with other multi-wavelength data, to show conclusively that Eddington ratio (the efficiency of BH accretion) is the main driver of EV1. They also found that orientation plays an important role in shaping the width of the main sequence, implying a flattened structure of the broad line region gas. Their work, published in the September 11 issue of the journal Nature, has profound implications for quasar research, and motivates theoretical studies of the inner structure of quasars to explain this simple unification scheme of quasar phenomenology with accretion and orientation. 

Figure caption (above)The distribution of about 20,000 luminous Sloan Digital Sky Survey quasars in the two-dimensional space of broad line width versus FeII strength, color-coded by the strength of the narrow [OIII] line emission. The strong horizontal trend is the main sequence of quasars driven by the efficiency of the black hole accretion, while the vertical spread of broad line width is largely due to our viewing angle to the inner region of the quasar.

Original Nature articlehttp://www.nature.com/nature/journal/v513/n7517/full/nature13712.html

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