Evidence for a Stratified Accretion Disk Wind in AGN

TL;DR

This paper provides observational evidence for a stratified, multi-zone accretion disk wind in AGN, revealing different outflow velocities and ionization states across emission line regions, consistent with radiatively driven wind models.

Contribution

It offers new observational constraints on the geometry and physical conditions of stratified AGN winds based on multi-wavelength spectroscopic analysis.

Findings

High-ionization lines show strong blueshifts and asymmetric profiles.

Low-ionization lines are more symmetric but exhibit systematic blueshifts.

Intermediate ionization lines have shifts between high and low ionization lines.

Abstract

We present observational evidence supporting the presence of a stratified accretion disk wind in active galactic nuclei (AGN), based on multi-wavelength spectroscopic analysis of broad and narrow emission lines. The diversity in emission line profiles, ionization potentials, and kinematic signatures suggests a structured outflow emerging from the accretion disk, with different zones contributing to specific spectral features. High-ionization lines (e.g., Civ {\lambda}1549) exhibit strong blueshifts and asymmetric profiles indicative of fast, inner winds, while low-ionization lines (e.g., H\b{eta}, Mgii {\lambda} 2800) show more symmetric profiles consistent with predominant emission from slower, denser regions farther out, although exhibiting systematic blueshifts in quasars radiating at high Eddington ratios. The intermediate ionization lines (e.g., Aliii {\lambda}1860) present a situation that is intermediate in terms of shift amplitudes, although in several super-Eddington candidates radial outflow velocity may reach values comparable to the ones of the high ionization lines. These results are consistent with radiatively driven wind models featuring radial stratification. We made preliminary photoionization modeling assuming unabsorbed radiation emitted from the corona and the hotter disk regions emission or absorbed by a layer of gas. Our findings provide new constraints on the geometry and physical conditions of AGN winds, providing clear evidence in favor of stratified wind emission.