Photoionisation modelling of the H II regions surrounding star-forming regions within the metallicity range Z=0.003-0.012

Abstract

We present the new approach to the ionisation structure modelling for the high-metallicity H II regions. The method is based on the multicomponent photoionisation modelling (MPhM) of these objects that takes into account their complicate structure due to superwind from the central star-forming region. The complex structure of H II region has been divided into internal and external components. Internal components correspond to the region of free expanding superwind and the cavity of superwind, respectively, while the external ones — to a thick layer of gas compressed by a superwind shock, and hydrodynamically undisturbed outer part of H II region, where the most of observed strong emission lines are formed. The components of the model were calculated within the assumption of spherical symmetry. The gas photoinisation was caused by the ionising quanta of both direct and diffuse ionising radiation. The fluxes of this radiation were calculated during the simulation using the radiative transfer equations which account for all important processes in the H II region causing this transfer. The diffuse ionising radiation was calculated in the Outward Only approach. In the region of free expansion of the superwind the chemical abundances were determined using the evolutionary population synthesis models of a star-forming region. The distributions of the electron temperature and density in the external components were obtained in such modelling as the solutions of the photoionisation energy balance equation. The stop criterion for evolutionary modelling corresponding to the condition of equilibrium of pressure on the boundary between the third and fourth components was adopted. The evolutionary grid of multicomponent high-metallicity models of the H II regions was calculated. It was shown that the internal structure of a H II region under certain conditions can cause the lack of quanta in the spectrum of ionising radiation.