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2008MNRAS.384.1427R - Mon. Not. R. Astron. Soc., 384, 1427-1436 (2008/March-2)
Star formation, metallicity gradient and ionized gas: clues to the formation of the elliptical galaxies NGC6868 and 5903.
RICKES M.G., PASTORIZA M.G. and BONATTO C.
Abstract (from CDS):
We have estimated the metallicity of the galaxies using single-aged stellar population (SSP) models. The central region of NGC6868 (|R| ≲ 0.5kpc) presents a deficiency of alpha elements with respect to iron and solar metallicity. The external parts present a roughly uniform distribution of [α/Fe] ratios and metallicities ranging from [Z/Z☉] = - 0.33 and solar. A similar conclusion applies to NGC5903.
Concerning the emitting gas conspicuously detected in NGC6868, we test three hypotheses as ionizing source: an HII region, post-AGB (asymptotic giant branch) stars and an active galactic nucleus (AGN). Diagnostic diagrams involving the ratios ([Nii]λ6584)/(Hα), ([Oi]λ6300)/(Hα) and ([Sii]λλ6717, 6731)/(Hα) indicate that values measured in the central region of NGC6868 are typical of LINERs (Low-Ionization Nuclear Emission-Line Regions). Together with the stellar population synthesis, this result suggests that the main source of gas ionization in NGC6868 is non-thermal, produced by a low-luminosity AGN, probably with some contribution of shocks to explain ionization at distances of ∼3.5kpc from the nucleus.
Abstract Copyright: 2008 The Authors. Journal compilation © 2008 RAS
Journal keyword(s): galaxies: fundamental parameters - galaxies: individual: NGC6868 - galaxies: individual: NGC5903
Simbad objects: 10
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