The inner bulge of M31

Two sets of long-slit spectra are used to investigate the stellar content of the M31 inner bulge. Spectra recorded with 2.0 Angstrom FWHM resolution near 4000 Angstrom are used to measure indices in the Rose [AJ, 89, 1238 (1984)] system out to 60 arcsec from the galaxy center along the north/south and east/west axes. Spectra with 14 Angstrom FWHM resolution near 5500 Angstrom are used to measure indices in the Lick system [Worthey et al., ApJS, 94, 687 (1994)] at 156 points in a 20X60 arcsec area centered on the nucleus. Systematic gradients, in the sense of weaker absorption features with increasing radius, are detected in both datasets, and the majority of gradients differ from zero at the 3 sigma or higher level. The gradients in M31 tend to be shallower than those in elliptical galaxies for example, Delta Mg-2/Delta log(r)= -0.015+/-0.001 in M31 and -0.062+/-0.009 in nearby elliptical galaxies without strong line emission. Comparisons with globular cluster sequences indicate that the integrated M31 bulge spectrum at 4000 Angstrom is dominated by a mixture of dwarfs and giants similar to that in globular clusters. The spectra also show enhanced 3883 Angstrom CN absorption similar in strength to that seen in M31 globular clusters, suggesting that the CNO enrichment histories of the M31 bulge and globular cluster system are related, and systematically different from the Galactic cluster system. The spatial distribution of H beta absorption is different from H alpha, a result that is attributed to line emission. Comparisons with models generated by Worthey [APJS, 95, 107 (1994)], Buzzoni et al. [AJ, 107, 513 (1994)], and Buzzoni et al. [AJ, 103, 1814 (1992)] suggest that [M/H], mean age, and [Mg/Fe] all change with distance from the center of M31, in the sense of younger, more iron-rich populations with lower [Mg/Fe] at smaller radii. When compared with line indices measured in the nearby elliptical galaxies NGC 3379 and NGC 4472, these same models predict that age and [Mg/Fe] likely do not vary with radius. The strength of the metallicity gradient in the central regions of M31 is estimated by a direct comparison with the Worthey [ApJS, 95, 107 (1994)] models, a procedure that automatically takes into account any variation of mean age with radius, with the result that Delta[Fe/H]/Delta log(r)similar to-0.5. This is significantly shallower than what is measured in the outer regions of the Galactic bulge. (C) 1997 American Astronomical Society.