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

Abstract

Abstract The nearby (∼500 kpc) metal-poor ([Fe/H] ≈ –1.2; Z ≈ 30% Z ⊙) 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 (J, H, and K) and the Spitzer Space Telescope (IRAC 3.6, 4.5, 5.8, and 8.0 μm and MIPS 24 μm). 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 1292 RSG candidates, 1050 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 ± 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.