THE LUMINOSITY DEPENDENCE OF ULTRAVIOLET ABSORPTION IN ACTIVE GALACTIC NUCLEI

摘要

We describe the results of a survey of the UV absorption properties of the Boroson & Green sample of active galactic nuclei (AGNs), which extends from the Seyfert (My approx= -21) to the luminous quasar (M_V approx= -27) level. The survey is based mostly on Hubble Space Telescope archival data available for approx> 1/2 of the 87 sample objects. Our main result is that soft X-ray-weak quasars (SXWQs; 10 AGNs with α_(ox) ≤ -2) show the strongest UV absorption at a given luminosity, and their maximum outflow velocity, v_(max), is strongly correlated with M_V (r_S= -0.95). This suggests that v_(max) is largely set by the luminosity, as expected for radiation pressure-driven outflows: Luminous SXWQs have preferentially low [O Ⅲ] luminosity, which suggests that they are physically distinct from unabsorbed AGNs, while non-SXWQs with UV absorption are consistent with being drawn from the unabsorbed AGN population. We also find an indication that v_(max)/v_(BLR) increases with L/L_( EDD), as expected for radiation pressure-driven outflows. This relation and the v_(max) versus M_V relation may indicate that the radiation-pressure force multiplier increases with luminosity and that the wind-launching radius in non-SXWQs is ～10 times larger than in SXWQs.