Anatomy of the AGN in NGC 5548: II. The Spatial, Temporal and Physical Nature of the Outflow from HST/COS Observations

TL;DR

This study analyzes UV spectra of NGC 5548's outflow over 16 years, revealing the physical structure, locations, and ionization changes of the AGN wind during a period of X-ray obscuration, using a fixed-column-density model.

Contribution

It introduces a simple, fixed-column-density absorber model that explains multi-epoch ionization states and outflow locations during variable X-ray obscuration in NGC 5548.

Findings

Main outflow component at 3.5±1 pc from the nucleus.

Additional components between 5-70 pc and beyond 100 pc.

First detection of C III* absorption troughs during the campaign.

Abstract

(Abridged) Our deep multiwavelength campaign on NGC 5548 revealed an unusually strong X-ray obscuration. The resulting dramatic decrease in incident ionizing flux allowed us to construct a comprehensive physical, spatial and temporal picture for the long-studied AGN wind in this object. Here we analyze the UV spectra of the outflow acquired during the campaign as well as from four previous epochs. We find that a simple model based on a fixed total column-density absorber, reacting to changes in ionizing illumination, matches the very different ionization states seen in five spectroscopic epochs spanning 16 years. Absorption troughs from C III* appeared for the first time during our campaign. From these troughs, we infer that the main outflow component is situated at 3.5+-1 pc from the central source. Three other components are situated between 5-70 pc and two are further than 100 pc. The wealth of observational constraints and the disparate relationship of the observed X-ray and UV flux between different epochs make our physical model a leading contender for interpreting trough variability data of quasar outflows.