Dusty Stellar Birth and Death in the Metal-Poor Galaxy NGC 6822

Abstract

The nearby ($\sim$500 kpc) metal-poor ([Fe/H] $\approx$ -1.2; $Z$ $\approx$ 30% $Z_{\odot }$) star-forming galaxy NGC 6822 has a metallicity similar to systems at the epoch of peak star formation. Through identification and study of dusty and dust-producing stars, it is therefore a useful laboratory to shed light on the dust life cycle in the early Universe. We present a catalog of sources combining near- and mid-IR photometry from the United Kingdom Infrared Telescope (UKIRT; $J$, $H$, and $K$) and the $Spitzer$ $Space$ $Telescope$ (IRAC 3.6, 4.5, 5.8, and 8.0 $\mu$m and MIPS 24 $\mu$m). This catalog is employed to identify dusty and evolved stars in NGC 6822 utilizing three color-magnitude diagrams (CMDs). With diagnostic CMDs covering a wavelength range spanning the near- and mid-IR, we develop color cuts using kernel density estimate (KDE) techniques to identify dust-producing evolved stars, including red supergiant (RSG) and thermally-pulsing asymptotic giant branch (TP-AGB) star candidates. In total, we report 1,292 RSG candidates, 1,050 oxygen-rich AGB star candidates, and 560 carbon-rich AGB star candidates with high confidence in NGC 6822. Our analysis of the AGB stars suggests a robust population inhabiting the central stellar bar of the galaxy, with a measured global stellar metallicity of [Fe/H] = -1.286 $\pm$ 0.095, consistent with previous studies. In addition, we identify 277 young stellar object (YSO) candidates. The detection of a large number of YSO candidates within a centrally-located, compact cluster reveals the existence of an embedded, high-mass star-formation region that has eluded previous detailed study. Spitzer I appears to be younger and more active than the other prominent star-forming regions in the galaxy.

arXiv commentAccepted for publication in The Astrophysical Journal; 27 pages, 13 figures, 12 tables (master catalog will be available from publisher)

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