A study of the stellar populations of M32 based on its spatially resolved spectrum

Abstract

view Abstract Citations (31) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of the Stellar Populations of M32 Based on its Spacially Resolved Spectrum Hardy, Eduardo ; Couture, Jean ; Couture, Christian ; Joncas, Gilles Abstract We present new spatially resolved spectroscopic observations of M32 in the 4000-6800 A spectral interval within a radial range of ~2r_e_. These observations breach the gap between the center of M32 and the outer regions which have recently been resolved into start. Using Bica and Alloin's spectral library we show by simple comparison that no globular cluster energy distribution matches the mean observed spectrum for any metallicity at any radial position. We then show that the addition of intermediate age populations allows an optimized solution that fits well the galaxy spectra. The conclusion that M32 is not an old single-age system akin to an overgrown globular cluster, nor a combination of such, is then inescapable in agreement with recent studies of its color- magnitude diagram. Next we use Pickles stellar library to obtain optimized solutions as function of position and thus evaluate the radial variation of age and metallicity. We find a well defined metallicity gradient {DELTA}[Fe/H]/{DELTA}log(r) = -0.25+/-0.07, for r >= 15" (i.e., 50 pc), which is similar to that of giant ellipticals. But we find no evidence for a significant variation in the Fe/Mg ratio, or of age, with radius. We confirm the existence of radial gradients of individual spectral features and find, for the first time, a radial gradient of the Mg_2_ feature. The latter translates into a metallicity gradient compatible with the one we derive from spectral synthesis. The central region within r~50 pc is peculiar in that most gradients appear only beyond this radial distance. Publication: The Astronomical Journal Pub Date: January 1994 DOI: 10.1086/116844 Bibcode: 1994AJ....107..195H Keywords: Color-Magnitude Diagram; Energy Spectra; Galactic Evolution; Galactic Structure; Line Spectra; Metallicity; Stellar Spectra; Abundance; Elliptical Galaxies; Energy Distribution; Luminosity; Spectrum Analysis; Stellar Spectrophotometry; Astrophysics; GLOBULAR CLUSTERS: INDIVIDUAL: M32 full text sources ADS | data products SIMBAD (7) NED (1)