Cold gas bubble inflated by a low-luminosity radio jet

TL;DR

This study reveals that low-luminosity radio jets can create expanding cold gas bubbles and significantly influence the gas dynamics and physical conditions in their host galaxies, impacting star formation and galaxy evolution.

Contribution

It provides the first clear detection of an expanding cold gas bubble driven by a low-luminosity radio jet, highlighting the jets' role in galaxy feedback processes.

Findings

Detection of a swiftly expanding molecular gas bubble with velocities up to 400 km/s.

High CO(2-1)/CO(1-0) line ratios indicating elevated gas excitation due to jet-ISM interaction.

Low-luminosity jets can significantly affect cold gas kinematics and conditions.

Abstract

We present NOEMA CO(2-1) observations of a nearby, young, low-luminosity radio source, B2 0258+35. Our earlier CO(1-0) study had shown the presence of strong jet-ISM interaction and a massive molecular gas outflow involving 75$\%$ of the circumnuclear gas. Our follow-up CO(2-1) observations have revealed even more complex gas kinematics, where the southern radio jet is driving out molecular gas in the form of a swiftly expanding bubble, with velocities up to almost 400 km s$^{-1}$. We found highly elevated CO(2-1)/CO(1-0) line ratios for the gas belonging to the bubble and also further away from the radio jets. Previous observations have shown that the active galactic nucleus (AGN) in the host galaxy, NGC 1167, is in a very low-accretion state. Thus, we attribute the high line ratios to the high gas excitation caused by the jet--ISM interaction. The radio jets, despite exhibiting a relatively low luminosity ($1.3 \times 10^{44}$ erg s$^{-1}$), are solely responsible for the observed extreme gas kinematics. This is one of the clearest detections of an expanding cold gas bubble in such a type of source, showing that the jets are affecting both the kinematics and physicals conditions of the gas. Our study adds to the growing store of evidence that low-luminosity radio sources can also affect the kinematics and physical conditions of the cold gas, which fuels star formation, in their host galaxies to a significant extent. Hence, such sources should be considered in models seeking to quantify feedback from radio AGN.