| Title: |
The dwarf irregular galaxy NGC 6822. II. Young, intermediate and old stellar populations: comparison between theory and observations |
| Authors: |
Tantalo, Maria, Bono, Giuseppe, Salaris, Maurizio, Pietrinferni, Adriano, Monelli, Matteo, Fabrizio, Michele, Braga, Vittorio F., Calamida, Annalisa, Dall'Ora, Massimo, D'Orazi, Valentina, Ferraro, Ivan, Fiorentino, Giuliana, Iannicola, Giacinto, Marengo, Massimo, Matsunaga, Noriyuki, Mullen, Joseph P., Stetson, Peter B. |
| Publication Year: |
2025 |
| Collection: |
Astrophysics |
| Subject Terms: |
Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics |
| More Details: |
This paper presents a quantitative analysis of the stellar content in the Local Group dwarf irregular galaxy NGC 6822 by comparing stellar evolution models and observations in color-magnitude diagrams (CMDs) and color-color diagrams (CC-Ds). Our analysis is based on optical ground-based g,r,i photometry, and deep archive HST photometry of two fields in the galaxy disk. We compared young, intermediate-age, and old stellar populations with isochrones from the BaSTI-IAC library and found that NGC 6822 hosts a quite metal-rich ([Fe/H] = -0.7 to -0.4) young component with an age ranging from 20 to 100 Myr. The intermediate-age population experienced a modest chemical enrichment between 4 and 8 Gyr ago while stars older than 11 Gyr have a low metal abundance ([Fe/H] ~ -1.70). We also identified the AGB clump population with a luminosity peak at i ~ 23.35 mag. Our analysis of both the CMD and the optical-NIR-MIR CC-Ds of AGB oxygen- and carbon-rich stars, using the PARSEC+COLIBRI isochrones with and without circumstellar dust, reveal that this stellar component exhibits a spread in age from 1 to 2 Gyr and in metallicity between [Fe/H]=-1.30 and -1.70. The stellar models we used reproduce very well the two distinct color sequences defined by AGB O- and C-rich stars in the various optical-NIR-MIR CC-Ds, suggesting that they are reliable diagnostics to identify and characterise intermediate-age stellar populations. However, we also find that evolutionary prescriptions in the optical i-(r-i) CMDs predict, at fixed color, systematically lower luminosities than observed AGB stars.
Comment: Accepted for publication in ApJ; 29 pages, 18 figures, 2 tables |
| Document Type: |
Working Paper |
| Access URL: |
http://arxiv.org/abs/2503.03451 |
| Accession Number: |
edsarx.2503.03451 |
| Database: |
arXiv |
