Physical Conditions in Quasar Outflows: Very Large Telescope Observations of QSO 2359-1241

We analyze the physical conditions of the outflow seen in QSO 2359-1241 (NVSS J235953-124148), based on high-resolution spectroscopic VLT observations. This object was previously studied using Keck HIRES data. The main improvement over the HIRES results is our ability to accurately determine the number density of the outflow. For the major absorption component, the populations from five different Fe II excited levels yield a gas density n(H) = 10(4.4) cm(-3) with less than 20% scatter. We find that the Fe II absorption arises from a region with roughly constant conditions and temperature greater than 9000 K, before the ionization front where temperature and electron density drop. Further, we model the observed spectra and investigate the effects of varying gas metallicities and the spectral energy distribution of the incident ionizing radiation field. The accurately measured column densities allow us to determine the ionization parameter (log U-H approximate to -2.4) and total column density of the outflow [log N-H(cm(-2)) approximate to 20.6]. Combined with the number density finding, these are stepping stones toward determining the mass flux and kinetic luminosity of the outflow, and therefore its importance to AGN feedback processes.