JWST MIRI and NIRCam unveil previously unseen infrared stellar populations in NGC 6822

June 2024 • 2024MNRAS.531..183N

Authors • Nally, Conor • Jones, Olivia C. • Lenkić, Laura • Habel, Nolan • Hirschauer, Alec S. • Meixner, Margaret • Kavanagh, P. J. • Boyer, Martha L. • Ferguson, Annette M. N. • Sargent, B. A. • Nayak, Omnarayani • Temim, Tea

Abstract • NGC 6822 is a nearby (~490 kpc) non-interacting low-metallicity (0.2 Z_⊙) dwarf galaxy which hosts several prominent H II regions, including sites of highly embedded active star formation. In this work, we present an imaging survey of NGC 6822 conducted with the Near Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) onboard JWST. We describe the data reduction, source extraction, and stellar population identifications from combined near- and mid-infrared (IR) photometry. Our NIRCam observations reach 7 mag deeper than previous JHK_s surveys of this galaxy, which were sensitive to just below the tip of the red giant branch (TRGB). These JWST observations thus reveal for the first time in the near-IR the red clump stellar population and extend nearly 3 mag deeper. In the mid-IR, we observe roughly 2 mag below the TRGB with the MIRI F770W and F1000W filters. With these improvements in sensitivity, we produce a catalogue of ~900 000 point sources over an area of ~6.0 × 4.3 arcmin². We present several NIRCam and MIRI colour-magnitude diagrams and discuss which colour combinations provide useful separations of various stellar populations to aid in future JWST observation planning. Finally, we find populations of carbon- and oxygen-rich asymptotic giant branch stars which will assist in improving our understanding of dust production in low-metallicity, early Universe analogue galaxies.

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Laura Lenkic