2012A&A...543A..35J

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 NGC205. 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. We identified 1,550 C stars in NGC205 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 NGC205, 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 NGC205 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 NGC147 and NGC185. 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 NGC205. The bolometric luminosity function for M-giant stars extends to M_bol=-6.0mag, 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 NGC147 and NGC185.