Outflow Kinematics Manifested by the Hα Line: Gas Outflows in Type 2 AGNs. IV.

Abstract

Energetic ionized gas outflows driven by active galactic nuclei (AGNs) 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 nonvirial 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 comparing them with those of [O III]. Using the spatially integrated spectra of similar to 37,000 Type 2 AGNs at z < 0.3 selected from the Sloan Digital Sky Survey DR7, we find a nonlinear correlation between H alpha velocity dispersion and stellar velocity dispersion that reveals the presence of the nongravitational 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].