Asymptotic giant branch stars in the central regions of M32

Abstract

We discuss high-resolution (FWHM ~ 0.4") near-infrared images of the central regions of the Local Group compact elliptical galaxy M32. The data are used to study the photometric properties of bright asymptotic giant branch stars in three annuli located within 30" of the galaxy center. The brightest AGB stars in each annulus occur near I ~ 19, and hence are roughly a magnitude brighter than the brightest stars in a field 2' from the galaxy center. The brightness of the AGB tip is similar to what is seen in galaxies which contain intermediate-age populations, strongly suggesting that an intermediate-age component is also present in the central regions of M32. The I luminosity function in each annulus follows a power law with logarithmic slope {DELTA} log (n)/{DELTA}I ~1.6 in the interval 19> I > 20. There is also a tendency for the color of the ridge line of luminous giants to become bluer with increasing distance from the center of M32, suggesting that a metallicity gradient is present. Finally, it is noted that the presence of an intermediate-age population in the center of M32 suggests that the substructures which have been detected in the central regions of many galaxies may have formed during relatively recent epochs.