The ionized gas at the center of IC 10: A possible localized chemical pollution by Wolf-Rayet stars

TL;DR

This study uses integral field spectroscopy to analyze the ionized gas in IC 10's starburst region, revealing localized chemical pollution likely caused by Wolf-Rayet stars, with implications for abundance measurements in galaxies.

Contribution

It provides the first spatially resolved evidence of localized chemical enrichment by Wolf-Rayet stars in a starburst galaxy.

Findings

Detection of broad He II 4686 emission indicating a Wolf-Rayet star.

Localized nitrogen and helium enrichment near WR features.

Ionization degree affects empirical oxygen abundance calibrations.

Abstract

We present results from integral field spectroscopy with the Potsdam Multi-Aperture Spectrograph at the 3.5m telescope at Calar Alto Observatory of the intense star-forming region [HL90] 111 at the center of the starburst galaxy IC 10. We have obtained maps with a spatial sampling of 1" x 1" = 3.9 pc x 3.9 pc of different emission lines and analyzed the extinction, physical conditions, nature of the ionization, and chemical abundances of the ionized gas, as well determined locally the age of the most recent star-formation event. By defining several apertures, we study the main integrated properties of some regions within [HL90] 111. Two contiguous spaxels show an unambiguous detection of the broad He II 4686 emission line, this feature seems to be produced by a single WNL star. We also report a probable N and He enrichment in the precise spaxels where the WR features are detected. The enrichment pattern is roughly consistent with that expected for the pollution of the ejecta of a single or a very small number of WR stars. Furthermore, this chemical pollution is very localized (~2"~7.8 pc) and it should be difficult to detect in star-forming galaxies beyond the Local Volume. We also discuss the use of the most-common empirical calibrations to estimate the oxygen abundances of the ionized gas in nearby galaxies from 2D spectroscopic data. The ionization degree of the gas plays an important role when applying these empirical methods, as they tend to give lower oxygen abundances with increasing ionization degree.