paper

The Evolved Stellar Content of NGC 147, NGC 185, and NGC 205

arXiv:astro-ph/0509612 · doi:10.1086/491706

Abstract

Broad-band near-infrared images are used to probe the photometric properties of the brightest asymptotic giant branch (AGB) stars within 2 arcminutes of the centers of the dwarf elliptical galaxies NGC 147, NGC 185, and NGC 205. Based on the peak brightness and color of the M giant sequences, ages of 1 Gyr and 0.1 Gyr are predicted for the most recent significant star forming events in NGC 185 and NGC 205, respectively. The brightest AGB stars in NGC 147 indicate that the most recent significant star-forming activity in that galaxy occured \~3 Gyr in the past. The specific frequency of C stars outside of the areas of most recent star formation is found to agree in all three galaxies. The fractional contribution made by C stars to the total AGB light in the K-band is found to be highest in NGC 147 and lowest in the central regions of NGC 205, which is qualitatively consistent with model predictions. The fractional contribution that C stars make to the total K-band light is found to be constant both within and between galaxies, with C stars contributing 2% of the total K-band light. It is concluded that, when averaged over timescales of a few Gyr, these galaxies have turned similar fractions of gas and dust, normalised according to total galaxy mass, into stars.

To appear in the Astronomical Journal

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