Evolution of blister-type H II regions in a magnetized medium

We use the three-dimensional Athena ionizing radiation-magnetohydrodynamics code to simulate blister-type H II regions driven by stars on the edge of magnetized gas clouds. We compare these to simulations of spherical H II regions where the star is embedded deep within a cloud, and to non-magnetized simulations of both types, in order to compare their ability to drive turbulence and influence star formation. We find that magnetized blister H II regions can be very efficient at injecting energy into clouds. This is partly a magnetic effect: the magnetic energy added to a cloud by an H II region is comparable to or larger than the kinetic energy, and magnetic fields can also help collimate the ejected gas, increasing its energy yield. As a result of these effects, a blister H II region expanding into a cloud with a magnetic field perpendicular to its edge injects twice as much energy by 5 Myr as a non-magnetized blister H II region driven by a star of the same luminosity. Blister H II regions are also more efficient at injecting kinetic energy than spherical H II regions, due to the recoil provided by escaping gas, but not as much as predicted by some analytic approximations.