Ionised gas outflows over the radio AGN life cycle

Feedback from active galactic nuclei (AGN) is known to affect the host galaxy’s evolution. In radio AGN, one manifestation of feedback is seen in gas outflows. However, it is still not well understood whether the effect of feedback evolves with the radio AGN life cycle. In this study, we aim to investigate this link using the radio spectral shape as a proxy for the evolutionary stage of the AGN. We used [O III] emission line spectra to trace the presence of outflows on the ionised gas. Using a sample of uniformly selected 129 radio AGN with L1.4 GHz ≈ 1023 − 1026 W Hz−1, and a mean stacking analysis of the [O III] profile, we conclude that the ionised gas outflow is linked to the radio spectral shape, and it evolves with the evolution of the radio source. We find that sources with a peak in their radio spectra (optically thick), on average, drive a broad outflow (FWHM ≈ 1330  ±  418 km s−1) with a velocity vout ≈ 240 km s−1. However, we detect no outflow in the stacked [O III] profile of sources without a peak in their radio spectrum (optically thin). We estimate a mass outflow rate of 0.09 − 0.41 M⊙ yr−1, and a kinetic power of 0.1 − 1.8 × 1041 erg s−1 for the outflow. In addition, we find that individual outflow detections are kinematically more extreme in peaked than non-peaked sources. We conclude that radio jets are most effective at driving gas outflows when young, and the outflow is typically short lived. Our stacking analysis shows no significant dependence of the presence of ionised gas outflows on the radio morphology, 1.4 GHz luminosity, optical luminosity and Eddington ratio of these sources. This suggests that in our sample, these properties do not play a defining role in driving the impact of the nuclear activity on the surrounding gas. We also identify candidate restarted AGN in our sample, whose [O III] profiles suggest that they have more disturbed gas kinematics than their evolved counterparts, although the evidence for this is tentative. Our findings support the picture where the impact of AGN feedback changes as the source evolves, and young radio jets interact with the ambient medium, clearing a channel of gas as they expand.