Radiationmagnetohydrodynamic simulations of the photoionization of magnetized globules

We present the results of radiation-magnetohydrodynamic simulations of the formation and expansion of H II regions and their surrounding photodissociation regions (PDRs) in turbulent, magnetised, molecular clouds on scales of up to 4 parsecs. We include the effects of ionising and non-ionising ultraviolet radiation and x rays from population synthesis models of young star clusters. For all our simulations we find that the H II region expansion reduces the disordered component of the magnetic field, imposing a large-scale order on the field around its border, with the field in the neutral gas tending to lie along the ionisation front, while the field in the ionised gas tends to be perpendicular to the front. The highest pressure compressed neutral and molecular gas is driven towards approximate equipartition between thermal, magnetic, and turbulent energy densities, whereas lower pressure neutral/molecular gas bifurcates into, on the one hand, quiescent, magnetically dominated regions, and, on the other hand, turbulent, demagnetised regions. The ionised gas shows approximate equipartition between thermal and turbulent energy densities, but with magnetic energy densities that are 1 to 3 orders of magnitude lower. A high velocity dispersion ( ∼ 8 km s−1) is maintained in the ionised ga