Outflow kinematics manifested by the H-alpha line: gas outflows in Type 2 AGNs. IV

TL;DR

This study investigates the kinematics of H-alpha emission in Type 2 AGNs to understand gas outflows driven by active galactic nuclei, revealing that H-alpha line profiles show evidence of outflows, albeit weaker than those seen in [O III].

Contribution

It provides the first large-scale statistical analysis of H-alpha kinematics in AGNs, comparing them with [O III] to assess outflow effects on hydrogen gas.

Findings

H-alpha velocity dispersion correlates non-linearly with stellar velocity dispersion.

Large H-alpha velocity shifts indicate AGN-driven outflows.

Outflow effects on H-alpha are weaker than on [O III].

Abstract

Energetic ionized gas outflows driven by active galactic nuclei (AGN) have been studied as a key phenomenon related to AGN feedback. To probe the kinematics of the gas in the narrow line region, [O III] ${\lambda}$5007 has been utilized in a number of studies, showing non-virial kinematic properties due to AGN outflows. In this paper, we statistically investigate whether the H-alpha emission line is influenced by AGN driven outflows, by measuring the kinematic properties based on the H-alpha line profile, and by comparing them with those of [O III]. Using the spatially integrated spectra of ~37,000 Type 2 AGNs at z < 0.3 selected from the SDSS DR7, we find a non-linear correlation between H-alpha velocity dispersion and stellar velocity dispersion, which reveals the presence of the non-gravitational component, especially for AGNs with a wing component in H-alpha. The large H-alpha velocity dispersion and velocity shift of luminous AGNs are clear evidence of AGN outflow impacts on hydrogen gas, while relatively smaller kinematic properties compared to those of [O III] imply that the observed outflow effect on the H-alpha line is weaker than the case of [O III].