Physical Conditions in Quasar Outflows: VLT Observations of QSO 2359-1241

TL;DR

This study uses high-resolution VLT spectra to precisely determine the physical conditions of a quasar outflow, improving upon previous measurements and aiding understanding of AGN feedback.

Contribution

The paper provides the first accurate density measurement of the outflow using Fe II level populations and models the outflow's physical conditions with considerations of metallicity and radiation field effects.

Findings

Number density n_H=10^4.4 cm^-3 with <20% scatter

Ionization parameter log(U)=-2.4, total column density log(N_H)=20.6 cm^-2

Outflow conditions are consistent with a region >9000 K before the ionization front

Abstract

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, level population from five different Fe II excited level yields 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 metalicities 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) = -2.4 and total column density of the outflow (log(N_H) = 20.6 cm^-2). Combined with the number density finding, these are stepping stones towards determining the mass flux and kinetic luminosity of the outflow, and therefore its importance to AGN feedback processes.