A study of photoionized gas in two HII regions of the N44 complex in the LMC using MUSE observations

TL;DR

This study uses MUSE observations and photoionization models to analyze the ionization structure and physical conditions of two HII regions in the N44 complex of the LMC, revealing their geometry and ionizing sources.

Contribution

First application of spatially resolved MUSE spectra combined with CLOUDY models to study ionization structures in N44 HII regions, identifying their geometries and ionizing sources.

Findings

N44 D1 is a Blister HII region with a stratified ionization structure.

N44 C shows interior patches of ionization emission without a clear boundary.

Ionization is mainly driven by O5 V star and local X-ray sources.

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 HII regions in 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] 6300A 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 HII region. The [O I] 6300A emission in N44 C does not provide a well-defined ionization front at the boundary, while patches of [S II] 6717 A and [O I] 6300A 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 HII regions. A spherically symmetric ionization-bounded model with a partial covering factor, which is appropriate for a Blister HII 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.