A Study of Photoionized Gas in Two H ii Regions of the N44 Complex in the LMC Using MUSE Observations

Abstract

We use the optical integral field observations with Multi-Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope, together with CLOUDY photoionization models, to study ionization structure and physical conditions of two luminous H ii regions in the N44 star-forming complex of the Large Magellanic Cloud. The spectral maps of various emission lines reveal a stratified ionization geometry in N44 D1. The spatial distribution of [O i] λ6300 emission in N44 D1 indicates a partially covered ionization front at the outer boundary of the H ii region. These observations reveal that N44 D1 is a blister H ii region. The [O i] λ6300 emission in N44 C does not provide a well-defined ionization front at the boundary, while patches of [S ii] λ6717 and [O i] λ6300 emission bars are found in the interior. The results of spatially resolved MUSE spectra are tested with the photoionization models for the first time in these H ii regions. A spherically symmetric ionization-bounded model with a partial covering factor, which is appropriate for a blister H ii region, can well reproduce the observed geometry and most of the diagnostic line ratios in N44 D1. Similarly, in N44 C we apply a low-density and optically thin model based on the observational signatures. Our modeling results show that the ionization structure and physical conditions of N44 D1 are mainly determined by the radiation from an O5 V star. However, local X-rays, possibly from supernovae or stellar wind, play a key role. In N44 C, the main contribution is from three ionizing stars.