Aims. We investigated the distribution of resolved asymptotic giant branch (AGB) stars over a much larger area than covered by previous near-infrared studies in the nearby dwarf elliptical galaxy NGC 205. Methods. Using data obtained with the WIRCam near-infrared imager of the CFHT, we selected the AGB stars in the JHK s color-magnitude diagrams, and separated the C stars from M-giant stars in the JHK s color-color diagram. Results. We identified 1,550 C stars in NGC 205 with a mean absolute magnitude of M Ks=-7.49 ± 0.54, and colors of (J-K s) 0 = 1.81 ± 0.41 and (H-K s) 0 = 0.76 ± 0.24. The ratio of C stars to M-giant stars was estimated to be 0.15 ± 0.01 in NGC 205, and the local C/M ratios for the southern region are somewhat lower than those for the northern region. The (J-K s) color distributions of AGB stars contain the main peak of the M-giant stars and the red tail of the C stars. A comparison of the theoretical isochrone models with the observed color distribution indicates that most of the bright M-giant stars in NGC 205 were formed at log (t yr) ∼ 9.0-9.7. The logarithmic slope of the M Ks luminosity function for M-giant stars was estimated to be 0.84 ± 0.01, which is comparable with dwarf elliptical galaxies NGC 147 and NGC 185. Furthermore, we found that the logarithmic slopes of the M Ks luminosity function for C and M-giant stars are different to places, implying a different star formation history within NGC 205. The bolometric luminosity function for M-giant stars extends to M bol =-6.0 mag, and that for C stars spans-5.6 < M bol <-3.0. The bolometric luminosity function of C stars is unlikely to be a Gaussian distribution and the mean bolometric magnitude of C stars is estimated to be M bol =-4.24 ± 0.55, which is consistent with our results for dwarf elliptical galaxies NGC 147 and NGC 185.
Bibliographical noteFunding Information:
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0021867). This work is partially supported by the KASI-Yonsei Joint Research Program (2010 − 2011) for the Frontiers of Astronomy and Space Science funded by the Korea Astronomy and Space Science Institute. M.Y. Jung is grateful for the support provided by the EU FP7 participation support program (2008 − 2011) of the National Research Foundation of Korea.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science