The Luminosity Dependence of Ultraviolet Absorption in Active Galactic Nuclei

Abstract

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 (M_V~=-21) to the luminous quasar (M_V~=-27) level. The survey is based mostly on Hubble Space Telescope archival data available for >~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.