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Star formation history and chemical enrichment in the nuclear regions of m31 and its dwarf companions m32 and ngc 205

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Star formation history and chemical enrichment in the nuclear regions of m31 and its dwarf companions m32 and ngc 205

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Título Star formation history and chemical enrichment in the nuclear regions of m31 and its dwarf companions m32 and ngc 205
Autor Bica, Eduardo Luiz Damiani
Alloin, Danielle Marie
Schmidt, Alex Andre
Abstract We present a comparative discussion about the stellar population and chemical enrichment in the nuclear regions of M 31 and of its dwarf companions M 32 and NGC 205, from a new set of long slit CCD spectra in the range 3500-10 000 Å. We have performed the population syntheses using a grid of star cluster spectral features as a function of age and metallicity. The algorithm is a multiple minimization procedure, including a statistical treatment of the acceptable solutions and for which we discuss as well the question of the uniqueness of the solution. It provides a more significant result with respect to classical minimization methods relying on a single optimal solution. We find that the semistellar nucleus (SSN) and the bulge of M 31 are dominated by old metal-rich populations. The overall enrichment in heavy elements is however larger in the SSN ([Z/Zʘ ] ~ 0.6 at least) than in the inner bulge ([Z/Zʘ ] = 0.3). In the visible, flux fractions of 10 to 20% arise from an intermediate age component. The old age components span the entire metallicity range, with a predominant contribution from the highly metallic ones. The young age component remains inconspicuous in the visible range. In the nucleus of M 32, the metal enrichment comes out to be around solar and the light is dominated by old components in the range -0.5 < [Z/Zʘ ] <O. As much as 30% ofthe flux at 5870 Å arises from an intermediate age component corresponding to a 15% mass fraction. Both the old metal-poor and the young components in M 32 contribute very little to the visible flux. Finally, our synthesis shows that the dominant population in the nucleus of NGC 205 is young, in the range 10⁸ to 510⁸ yr. The old component with metallicity -1 < [Z/Zʘ ] < -0.5 and the intermediate age components provide each around 20% of the visible light. The maximum metallicity attained in this object is [Z/Zʘ ] = -0.5.
Contido em Astronomy and Astrophysics. Berlin. Vol. 228, no. 1 (Feb. 1990), p. 23-26
Assunto Astrofisica
Estruturas galaticas
Evolucao galatica
Galaxias
Nucleo galatico
[en] Galaxies: evolution of
[en] Galaxies: M 31, M 32 and NGC 205
[en] Galaxies: nuclei of
[en] Galaxies: stellar content of
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/98029
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