The Distance of Quasar Outflows from the Central Source: The First Consistent Values from Emission and Absorption Determinations

Abstract

Measuring the distance of quasar outflows from the central source (R) is essential for determining their importance for active galactic nucleus feedback. There are two methods to measure R: (1) a direct determination using spatially resolved integral field spectroscopy (IFS) of the outflow in emission and (2) an indirect method that uses the absorption troughs from ionic excited states. The column density ratio between the excited and resonance states yields the outflow number density. Combined with a knowledge of the outflow’s ionization parameter, R can be determined. Generally, the IFS method probes an R range of several kiloparsecs or more, while the absorption method usually yields R values of less than 1 kpc. There is no inconsistency between the two methods as the determinations come from different objects. Here we report the results of applying both methods to the same quasar outflow, where we derive consistent determinations of R ≈ 5 kpc. This is the first time that the indirect absorption R determination is verified by a direct spatially resolved IFS observation. In addition, the velocities (and energetics) from the IFS and absorption data are found to be consistent. Therefore, these are two manifestations of the same outflow. In this paper we concentrate on the absorption R determination for the outflow seen in quasar 3C 191 using Very Large Telescope/X-shooter observations. We also reanalyze an older absorption determination for the outflow based on Keck/High Resolution Echelle Spectrometer data and find the revised measurement to be consistent with ours. Our companion paper details the IFS analysis of the same object.