Tantalo, M, Dall'Ora, M, Bono, G, Stetson, PB, Fabrizio, M, Ferraro, I, Nonino, M, Braga, VF, Silva, RD, Fiorentino, G, Iannicola, G, Marengo, M, Monelli, M, Mullen, JP, Pietrinferni, A and Salaris, M (2022) On the Dwarf Irregular Galaxy NGC 6822. I. Young, Intermediate, and Old Stellar Populations. Astrophysical Journal, 933 (2). ISSN 0004-637X

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Abstract

We present accurate and deep multiband (g, r, i) photometry of the Local Group dwarf irregular galaxy NGC 6822. The images were collected with wide-field cameras at 2 m/4 m (INT, CTIO, CFHT) and 8 m class telescopes (Subaru) covering a 2 deg2 field of view across the center of the galaxy. We performed point-spread function photometry of ≈7000 CCD images, and the final catalog includes more than 1 million objects. We developed a new approach to identify candidate field and galaxy stars and performed a new estimate of the galaxy center by using old stellar tracers, finding that it differs by 1.′15 (R.A.) and 1.′53 (decl.) from previous estimates. We also found that young (main sequence, red supergiants), intermediate (red clump, asymptotic giant branch (AGB)), and old (red giant branch) stars display different radial distributions. The old stellar population is spherically distributed and extends to radial distances larger than previously estimated (∼1°). The young population shows a well-defined bar and a disk-like distribution, as suggested by radio measurements, that is off-center compared with the old population. We discuss pros and cons of the different diagnostics adopted to identify AGB stars and develop new ones based on optical-near-IR-mid-IR color-color diagrams to characterize oxygen- and carbon-rich stars. We found a mean population ratio between carbon and M-type (C/M) stars of 0.67 ± 0.08 (optical/near-IR/mid-IR), and we used the observed C/M ratio with empirical C/M-metallicity relations to estimate a mean iron abundance of [Fe/H] ∼-1.25 (σ = 0.04 dex), which agrees quite well with literature estimates.

Item Type:	Article
Uncontrolled Keywords:	Astronomy & Astrophysics; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural)
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society; IOP Publishing
SWORD Depositor:	A Symplectic
Date Deposited:	07 Nov 2022 14:47
Last Modified:	07 Nov 2022 15:00
DOI or ID number:	10.3847/1538-4357/ac7468
URI:	https://researchonline.ljmu.ac.uk/id/eprint/18049

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