The parsec-scale structure of jet-driven HI outflows in radio galaxies

TL;DR

This study uses high-resolution VLBI observations to investigate how radio jets influence surrounding HI gas in galaxies, confirming that young jets drive outflows and affect gas turbulence.

Contribution

It provides observational evidence linking jet age and power to HI outflow presence and properties, testing and supporting recent simulation predictions.

Findings

Young radio jets are associated with stronger HI outflows.

HI outflows are clumpy and close to the nucleus, indicating strong jet-gas interactions.

Low-power jets may increase turbulence without producing outflows.

Abstract

Radio jets can play multiple roles in the feedback loop by regulating the accretion of the gas, by enhancing gas turbulence, and by driving gas outflows. Numerical simulations are beginning to make detailed predictions about these processes. Using high resolution VLBI observations we test these predictions by studying how radio jets of different power and in different phases of evolution affect the properties and kinematics of the surrounding HI gas. Consistent with predictions, we find that young (or recently restarted) radio jets have stronger impact as shown by the presence of HI outflows. The outflowing medium is clumpy {with clouds of with sizes up to a few tens of pc and mass ~10^4 m_sun) already in the region close to the nucleus ($< 100$ pc), making the jet interact strongly and shock the surrounding gas. We present a case of a low-power jet where, as suggested by the simulations, the injection of energy may produce an increase in the turbulence of the medium instead of an outflow.