The Evolved Red Stellar Content of M32

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Abstract
Near‐infrared images obtained with the Canada‐France‐Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) are used to investigate the stellar content of the Local Group compact elliptical galaxy M32. Observations of a field 23 from the galaxy center reveal a large population of asymptotic giant branch (AGB) stars, and comparisons with models indicate that these objects have an age log (tGyr)≤9.3. The AGB population is very homogeneous, with Δlog (tGyr)≤ ± 0.1 dex and Δ[M/H]≤ ± 0.3 dex. The reddest AGB stars have J−K≤1.5, and it is suggested that the very red stars seen in earlier, less deep, surveys are the result of large photometric errors. The bolometric AGB luminosity function (LF) of this field is in excellent agreement with that of the Galactic bulge. Based on the integrated brightness of AGB stars brighter than the red giant branch tip, which occurs at K = 17.8, it is concluded that intermediate‐age stars account for roughly 25% of the total K light and 10% ± 5% of the total mass in this field. A field close to the center of M32 was also observed. The brightest stars within a few arcseconds of the nucleus have K = 15.5, and the density of these objects is consistent with that predicted from the outer regions of the galaxy after scaling according to surface brightness. Moreover, the K luminosity function (LF) of bright sources between 20'' and 30'' of the nucleus is well matched by the LF of the outer regions of the galaxy after accounting for differences in surface brightness and correcting for the effects of crowding. It is concluded that the relative size of the intermediate‐age component with respect to other populations does not change with radius over much of the galaxy. However, the integrated J−K color and 2.3 μm CO index change with radius within a few tenths of an arcsecond of the galaxy center, indicating that, contrary to what might be inferred from observations at visible wavelengths, the integrated photometric properties of the central regions of M32 differ from those of the surrounding galaxy.
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