Insights into the collapse and expansion of molecular clouds in outflows from observable pressure gradients

The jets launched by actively accreting black holes can generate massive outflows in galaxies, which could suppress or enhance star formation by rarefying or compressing clouds of molecular gas. To study the stability of such jet-impacted clouds, we performed astrochemical, thermally balanced, radiative transfer modelling of the CO and HCO⁺ emission of the galaxy IC 5063. We found that jet-related mechanical heating and cosmic rays contribute to the molecular gas heating rate and could even individually sustain it. Clouds excited by these mechanisms have temperatures and densities reflecting an order-of-magnitude increase in their internal pressure. Variations of their external pressure, deduced from [S II] and [N II] ionized gas emission, further reveal that some clouds are undergoing rarefaction and others compression. Our work shows a new viewpoint on plausible links between galactic outflows and star formation conditions: that of observable pressure gradients. It also emphasizes the role of cosmic rays in contributing to these gradients.