Ionized Outflows from Compact Steep Spectrum Sources

TL;DR

This study investigates ionized gas outflows in young CSS radio galaxies, revealing complex velocity structures aligned with radio jets and a mix of ionization mechanisms, advancing understanding of AGN feedback in early-stage radio sources.

Contribution

It provides detailed integral field spectroscopic analysis of emission-line regions in CSS sources, linking outflow dynamics to radio jet activity and ionization processes.

Findings

Emission-line regions show multi-component velocity structures.

Velocity gradients align with radio jets, indicating jet-driven outflows.

Ionization is due to both AGN radiation and shocks.

Abstract

Massive outflows are known to exist, in the form of extended emission-line regions (EELRs), around about one-third of powerful FR II radio sources. We investigate the origin of these EELRs by studying the emission-line regions around compact-steep-spectrum (CSS) radio galaxies that are younger (10$^3$ to 10$^5$ years old) versions of the FR II radio galaxies. We have searched for and analyzed the emission-line regions around 11 CSS sources by taking integral field spectra using GMOS on Gemini North. We fit the [\ion{O}{3}] $\lambda 5007$ line and present the velocity maps for each detected emission-line region. We find, in most cases, that the emission-line regions have multi-component velocity structures with different velocity dispersions and/or flux distributions for each component. The velocity gradients of the emission-line gas are mostly well aligned with the radio axis, suggesting a direct causal link between the outflowing gas and the radio jets. The complex velocity structure may be a result of different driving mechanisms related to the onset of the radio jets. We also present the results from the line-ratio diagnostics we used to analyze the ionization mechanism of the extended gas, which supports the scenario where the emission-line regions are ionized by a combination of AGN radiation and shock excitation.