Linking pressure gradients with the stability of molecular clouds in
  galactic outflows
  The jets launched by actively accreting black holes are capable of launching
several of the massive (million or billion solar mass) molecular outflows
observed in galaxies. These outflows could suppress or enhance star formation
in galaxies. To investigate the stability of clouds capable to form stars in
outflows, we modeled CO and HCO+ ALMA data of the galaxy IC5063, in which
black-hole jets impact molecular clouds. Using a radiative transfer code that
self-consistently performs astrochemical and thermal balance calculations based
on the available gas heating sources, we found that mechanical heating and
cosmic ray (CR) heating are fully capable of individually reproducing the data.
In our best-fit model, CRs provide about 1/3rd of the dense gas heating at the
radio lobes, emphasizing the role of this often neglected mechanism in heating
the gas and potentially generating outflows. The gas temperature and density
indicate that the jet passage leads to an increase of about 1 order of
magnitude in the internal pressure Pi of molecular clouds (with Pi/k from
8*10^5 up to 7*10^6 K cm^-3), irrespective of the excitation mechanism. From
the fluxes of [S II] and [N II] lines in VLT MUSE data, the external pressure
Pe of molecular clouds increases in several regions enough to exceed Pi. This
result leads us to conclude that we are observing the expansion of an ionized
overpressurized cocoon that compresses molecular clouds and that could lead to
their collapse. Some jet-impacted clouds, nonetheless, near pathways that the
jet cleared have increased Pi and decreased Pe. They are likely to undergo
evaporation of their outer layers. Part of the evaporated layers could mass
load the outflow thanks to ram pressure from co-spatial ionized gas flows. The
observed pressure changes thus suggest that both star formation enhancement and
suppression could simultaneously occur.
