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arXiv · 2503.20551

Study of extragalactic HII regions with echelle spectroscopy: The A2 region in the irregular galaxy IC4662

Alexei Kniazev
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Abstract

I present the results of echelle spectroscopy of a bright HII region in the irregular galaxy IC4662 and their comparison with results from long-slit spectroscopy of the same region. All observations were obtained with the standard spectrographs of the SALT telescope: (1) low and medium spectral resolution spectrograph RSS (R~800) and (2) echelle spectrograph HRS (R=16000-17000). In both types of data the intensities of most of the emission lines were measured and abundances of oxygen and N, Ne, S, Ar, Cl and Fe were determined as well as physical parameters of the \ion{H}{ii} region. The chemical abundances were obtained from both types of data with the Te-method. Abundances calculated from both types of data agree to within the cited uncertainties. The analysis of the echelle data revealed three distinct kinematic subsystems within the studied \ion{H}{ii} region: a narrow component (NC, $σ~ 12$~km/s), a broad component (BC, $σ~ 40$~km/s), and a very broad component (VBC, $σ~ 60-110$~km/s, detected only in the brightest emission lines). The velocity dispersion dependence on the ionisation potential of elements showed no correlation for the NC, indicating a well-mixed turbulent medium, while the BC exhibited pronounced stratification, characteristic of an expanding shell. Based on a detailed analysis of the kinematics and chemical composition, it was concluded that the BC is associated with the region surrounding a Wolf-Rayet star of spectral type WN7-8. The stellar wind from this WR star interacts with a shell ejected during an earlier evolutionary stage (either as a red supergiant or a luminous blue variable, LBV), which is enriched in nitrogen. These findings highlight the importance of high spectral resolution for detecting small-scale (~25 pc) chemical inhomogeneities and for understanding the feedback mechanisms of massive stars in low-metallicity environments.

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Alexei Kniazev. 2025-03-26. Study of extragalactic HII regions with echelle spectroscopy: The A2 region in the irregular galaxy IC4662. https://arxiv.org/abs/2503.20551

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