The Stellar Population and Interstellar Medium in NGC 6822

Abstract

We present a comprehensive study of the stellar population and the interstellar medium in NGC 6822 using high-quality H I data (obtained with the Australia Telescope Compact Array) and optical broadband and narrowband data (obtained with Subaru and the Isaac Newton Telescope). Our Hα observations are an order of magnitude deeper than previous studies and reveal a complex filamentary network covering almost the entire central disk of NGC 6822. We find hitherto unknown H II regions in the outskirts of NGC 6822 and the companion galaxy. The old and intermediate-age stellar population can be traced out to radii of over 0°6 (>5 kpc), significantly more extended than the H I disk. In sharp contrast, the distribution of the young, blue stars closely follows the distribution of the H I disk and displays a highly structured morphology. We find evidence for an older stellar population in the companion galaxy; the current star formation activity, although likely to have been triggered by the interaction with NGC 6822, is not the first star formation episode in this object. We show that the properties of the giant kiloparsec-sized hole in the outer H I disk of NGC 6822 are consistent with it being formed by the effects of stellar evolution.