Bibcode
DOI
Rose, James A.; Arimoto, Nobuo; Caldwell, Nelson; Schiavon, Ricardo P.; Vazdekis, Alexandre; Yamada, Yoshihiko
Referencia bibliográfica
The Astronomical Journal, Volume 129, Issue 2, pp. 712-728.
Fecha de publicación:
2
2005
Número de citas
52
Número de citas referidas
44
Descripción
We present long-slit spectroscopy of the elliptical galaxy M32, obtained
with the 8 m Subaru telescope at Mauna Kea, the 1.5 m Tillinghast
telescope at the F. L. Whipple Observatory, and the 4 m Mayall telescope
at the Kitt Peak National Observatory. The spectra cover the Lick index
red spectral region, as well as higher order Balmer lines in the blue.
Spectra have been taken with the slit offset from the nucleus to avoid
scattered-light contamination from the bright nucleus of M32. An
analysis of numerous absorption features, particularly involving the
Hγ and Hβ Balmer lines, reveals that systematic radial trends
are evident in the integrated spectrum of M32. Population synthesis
models indicate a radial change in both the age and chemical composition
of the light-weighted mean stellar population in M32, from the nucleus
out to 33", i.e., an approximately 1.0 effective radius, Re.
Specifically, the light-weighted mean stellar population at
1Re is older by ~3 Gyr and more metal-poor by about -0.25 dex
in [Fe/H] than the central value of ~4 Gyr and [Fe/H]~0.0. We show that
this apparent population trend cannot be attributed to a varying
contribution from either hot stars or emission-line contamination. The
increase in age and decrease in metal abundance with radius are
sufficiently well matched to explain the flat radial color profiles
previously observed in M32. In addition, the ratio of Mg to Fe
abundance, [Mg/Fe], increases from about -0.25 in the nucleus to about
-0.08 at 1Re. Finally, we find spuriously pronounced
line-strength gradients in the Mayall data that are an artifact of
scattered light from the bright nucleus. Scattered-light issues may
explain the lack of consistency among previously published studies of
radial line strength gradients in M32.