Tracing the outflow kinematics in Type 2 Active Galactic Nuclei

TL;DR

This study analyzes the outflow kinematics in Type 2 AGN spectra, revealing that non-gravitational outflows significantly influence emission line profiles, especially in [O III], with correlations indicating systemic outflow effects across different lines.

Contribution

It introduces a detailed decomposition method for emission lines in AGN spectra and demonstrates the systemic impact of outflows on line profiles across multiple emission lines.

Findings

Wing components exhibit pure non-gravitational kinematics.

Correlations between line shifts and widths indicate systemic outflow influence.

[O III] lines show the strongest outflow signatures with broadest wings.

Abstract

We have used the sample of 577 active galactic nuclei Type 1.8-2 spectra (z < 0.25), taken from Sloan Digital Sky Survey, to trace the influence of the outflow kinematics to the profiles of different emission lines (Hbeta, [O III], Halpha, [N II], [S II]). All considered lines were fitted with two Gaussian components: one which fits the core of the line, and another which fits the wings. We gave the procedure for decomposition of Halpha+[N II] wavelength band, for the spectra where these lines overlap. The influence of the gravitational/non-gravitational kinematics to the line components is investigated by comparing the dispersions of the line components with stellar velocity dispersion. We found that wing components of all considered emission lines have pure non-gravitational kinematics, the core components are consistent with gravitational kinematics for the Halpha, [N II] and [S II] lines, while in the [O III] there is evidence for contribution from non-gravitational kinematics. We adopted the wing components as proxy of the outflow contribution and we investigated the outflow kinematics by analysing the correlations between widths and between shifts of the wing components of different lines. We found the strong correlations between shifts and between wing component widths of all considered lines, with exception of the Hbeta wing component width. These correlations indicate that outflow dynamics systemically affects all emission lines in spectrum. However, it reflects with different strength in their profiles, which is observed as different widths of the wing components. The strongest outflow signature is observed in the [O III] lines, which have the broadest wing components, weaker in Halpha and [N II], and the weakest in [S II]. These results imply that considered lines arise in different parts of an outflowing region.