Space Telescope and Optical Reverberation Mapping Project. XI. Disk-wind characteristics and contributions to the very broad emission lines of NGC 5548

TL;DR

This study investigates how a translucent disk wind in NGC 5548 influences broad emission lines, revealing its role in shaping observed spectral features and emphasizing the need to consider such winds in active galactic nucleus models.

Contribution

It demonstrates that a translucent disk wind contributes to broad emission lines and affects spectral observations, advancing understanding of AGN wind impacts.

Findings

A translucent wind contributes to He II and Fe K? emission.

The wind has a modest optical depth to electron scattering.

It explains the very broad base in UV emission lines.

Abstract

In 2014 the NGC 5548 Space Telescope and Optical Reverberation Mapping campaign discovered a two-month anomaly when variations in the absorption and emission lines decorrelated from continuum variations. During this time the soft X-ray part of the intrinsic spectrum had been strongly absorbed by a line-of-sight (LOS) obscurer, which was interpreted as the upper part of a disk wind. Our first paper showed that changes in the LOS obscurer produce the decorrelation between the absorption lines and the continuum. A second study showed that the base of the wind shields the BLR, leading to the emission-line decorrelation. In that study, we proposed the wind is normally transparent with no effect on the spectrum. Changes in the wind properties alter its shielding and affect the SED striking the BLR, producing the observed decorrelations. In this work, we investigate the impact of a translucent wind on the emission lines. We simulate the obscuration using XMM-Newton, NuSTAR, and HST observations to determine the physical characteristics of the wind. We find that a translucent wind can contribute a part of the He II and Fe K? emission. It has a modest optical depth to electron scattering, which explains the fainter far-side emission in the observed velocity delay maps. The wind produces the very broad base seen in the UV emission lines and may also be present in the Fe K? line. Our results highlight the importance of accounting for the effects of such winds in the analysis of the physics of the central engine.