The Formation of Catastrophically Cooling Outflows in Star-forming Regions via Non-equilibrium Radiative Cooling

The Formation of Catastrophically Cooling Outflows in Star-forming Regions via Non-equilibrium Radiative Cooling

Multiwavelength surveys of star-forming regions suggest the presence of catastrophically cooling outflows, also sometimes accompanied by warm outflows and hot bubbles. Mechanical feedback from super star clusters in starburst regions can produce cooling galactic-scale outflows, but starburst-driven outflows predicted by the adiabatic fluid models cannot lead to very strong cooling seen in several star-forming galaxies such as M82 and NGC 2366. We therefore simulate starburst-driven outflows using  time-dependent non-equilibrium radiative cooling functions of the MAIHEM non-equilibrium package in the framework of the hydrodynamics code FLASH in order to determine the existence domains of strongly radiative cooling, so called catastrophic cooling, in the parameter space of the gas metallicity, outflow mass-loading, outflow kinetic heating efficiency, and ambient density. Although the gas metallicity has a major role in cooling, radiative cooling is significantly enhanced by increasing mass-loading and decreasing kinetic heating efficiency. Our simulations indicate hot bubbles may appear even with both the adiabatic and substantially radiative cooling outflows. Our results demonstrate the significance of non-equilibrium radiative cooling for star-forming regions, where coolants could be responsible for the build-up of cold molecular hydrogen (H₂) clumps that can trigger the formation of new stars as gravitational collapse occurs once the H₂ clump’s mass exceeds the Jeans critical mass.
 

Poster presented at Star Formation: From Clouds to Discs (dias.ie/cloudstodiscs), Dublin Institute for Advanced Studies, Malahide, Ireland, 18-21 October 2021