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Using a large sample of 26 623 quasars with redshifts in the range  1.5 ≤ z ≤ 5.1  with C  iv λ1549 Å emission line in Fifth Data Release of the Sloan Digital Sky Survey (SDSS), we investigate the cosmological evolution of the Baldwin effect, i.e. the relation between the equivalent width (EW) of the C  iv  emission line and continuum luminosity. We confirm the earlier result that there exists a strong correlation between the C  iv  EW and the continuum luminosity, and we find that, up to   z ≈ 5 , the slope of the Baldwin effect seems to have no effect of cosmological evolution. A subsample of 13 960 quasars with broad C  iv λ1549 Å emission line from SDSS is used to explore the origin of the Baldwin effect. We find that C  iv  EW have a strong correlation with the mass of supermassive black hole (SMBH), and a weak correlation with the Eddington ratio,   L  Bol / L  Edd  . This suggests that the SMBH mass is probably the primary drive for the Baldwin effect.

The origin and evolution of C iv Baldwin effect in QSOs from the Sloan Digital Sky Survey