Caltech/IPAC Lunch Seminar

A challenging problem in galactic astrophysics of how molecular gas can survive in the halos of galaxies without been promptly destroyed by hydrodynamic instabilities. Yet molecular gas is found in many hot haloes; from galactic outflows, to "Jellyfish" galaxies in larger cluster halos. I will discuss the discovery of cold and warm molecular hydrogen in the hot massive group halo of Stephan's Quintet. Based on new high-resolution ALMA CO observations, and JWST imaging and spectroscopy, I will show that significant amounts of molecular gas have survived a major shock wave passing through the halo of the group. Our JWST MRS observations show that although 30% of the shocked molecular hydrogen is strongly heated and decelerated in the main shock, the majority of the shocked warm gas has somehow survived, and is radiating strongly in the mid-IR. Compact clumps of even colder gas are also seen with ALMA. I will present some thoughts about how the molecular gas survives, including the idea that warm shocked gas is mixed with colder gas in turbulent mixing layers, allowing reformation of gas at the surface of the surviving clumps. The observations may help refine models of turbulent mixing, as well as providing a possible way that halo molecular gas might survive long enough to accrete onto galactic disks over cosmic time.