What controls the CIV line profile in active galactic nuclei?

The high-ionization lines in active galactic nuclei (AGN), such as C IV, tend to be blueshifted with respect to the lower-ionization lines, such as Hbeta, and often show a strong blue excess asymmetry not seen in the low-ionization lines. There is accumulating evidence that the Hbeta profile is dominated by gravity, and thus provides a useful estimate of the black hole mass in AGN. The shift and asymmetry commonly seen in C IV suggest that non-gravitational effects, such as obscuration and radiation pressure, may affect the line profile. We explore the relation between the Hbeta and CIV profiles using the ultraviolet (UV) spectra available for 81 of the 87 z less than or equal to 0.5 PG quasars in the Boroson & Green sample. We find the following. (1) Narrow C IV lines (full width at half-maximum, FWHM < 2000 km s(-1)) are rare (similar to 2 per cent occurrence rate) compared with narrow H lines ( 20 per cent). (2) In most objects where the H FWHM < 4000 km s(-1) the CIV line is broader than Hbeta, but the reverse is true when the Hbeta FWHM > 4000 km s(-1). This argues against the view that CIV generally originates closer to the centre, compared with H. (3) CIV appears to provide a significantly less accurate, and possibly biased estimate of the black hole mass in AGN, compared with H. (4) All objects where CIV is strongly blueshifted and asymmetric have a high L/L-Edd, but the reverse is not true. This suggests that a high L/L-Edd is a necessary but not sufficient condition for generating a blueshifted asymmetric C IV emission. (5) We also find indications for dust reddening and scattering in 'normal' AGN. In particular, PG quasars with a redder optical-UV continuum slope show weaker CIV emission, stronger C IV absorption and a higher optical continuum polarization.