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Tuesday 12 Nov 2019[Journal Club] Title: Photoionisation in Giant Molecular Cloud Complexes

Tom Bending - University of Exeter

Physics Building, 4th floor Interaction area 11:15-11:35

We present simulations of a 500 pc2 region, containing gas of mass 4 x 106 M?, extracted from a galaxy scale simulation, scaled up in resolution, including photoionising feedback from stars of mass > 20 M?. Our region is evolved for 10 Myr and shows clustered star formation along the arm generating ≈ 5000 cluster sink particles ≈ 5% of which contain at least one of the ≈ 4000 stars of mass > 20 M?. Photoionisation has a noticeable effect on the gas in the region, producing ionised cavities and leading to dense features at the edge of the ionisation regions. We quantify the effect of photoionisation by comparing the properties of clumps and clouds in the simulation. Photoionisation initially produces around 100% more clouds and clumps, but they are smaller and more broken up compared to the no feedback case. The total gas fraction in these clouds and clumps is also increased and they are less likely to be bound in the simulations with ionisation included. After this initial, photoionisation induced, peak of dense gas mass and the number of clouds and clumps, we see a rapid decrease in both. We also find that star formation is partially displaced throughout the spiral arm with up to 30% of our cluster sink mass located at distances > 5 pc from sites of sink formation in the absence of feedback. We demonstrate that star formation is accelerated by ionisation fronts interacting with surrounding gas, particularly when clouds are compressed from multiple sides by HII regions which often leads to clouds forming stars both several Myr sooner and more efficiently than they do without feedback. At later times, the star formation rate decreases to below that of the no feedback case.

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