Quasar outflows and AGN feedback in the extreme UV: HST/COS observations of HE 0238-1904

Spectroscopic observations of quasar outflows at rest-frame 500-1000Å have immense diagnostic power. We present analyses of such data, where absorption troughs from OIV and OIV* allow us to obtain the distance of the outflows from the AGN and troughs from Ne VIII and MgX reveal the warm absorber phase of the outflow. Their inferred column densities, combined with those of OVI, NIV and HI, yield two important results. (1) The outflow shows two ionization phases, where the high-ionization phase carries the bulk of the material. This is similar to the situation seen in X-ray warm absorber studies. Furthermore, the low-ionization phase is inferred to have a volume filling factor of 10^-5-10^-6. (2) We determine a distance of 3000 pc from the outflow to the central source using the OIV*/O IV column density ratio and the knowledge of the ionization parameter. Since this is a typical high-ionization outflow, we can determine robust values for the outflow's mass flux and kinetic luminosity of 40M_⊙ yr^-1 and 10⁴⁵ erg ^s-1, respectively, where the latter is roughly equal to 1 per cent of the bolometric luminosity. Such a large kinetic luminosity and mass flow rate measured in a typical high-ionization wind suggest that quasar outflows are a major contributor to AGN feedback mechanisms.