Galactic Chemical Evolution: Carbon through Zinc

Abstract

We calculate the evolution of heavy-element abundances from C to Zn in the solar neighborhood, adopting our new nucleosynthesis yields. Our yields are calculated for wide ranges of metallicity (Z ¼ 0YZ ) and the explosion energy (normal supernovae and hypernovae), based on the light-curve and spectra fitting of individual supernovae. The elemental abundance ratios are in good agreement with observations. Among the -elements, O, Mg, Si, S, and Ca show a plateau at ½Fe/H P À1, while Ti is underabundant overall. The observed abundance of Zn (½Zn/Fe $ 0) can be explained only by the high-energy explosion models, as it requires a large contribution of hypernovae. The observed decrease in the odd-Z elements (Na, Al, and Cu) toward low ½Fe/H is reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements (Cr, Mn, Co, and Ni) are consistent with the observed mean values at À2:5 P ½Fe/H P À1, and the observed trend at the lower metallicity can be explained by the energy effect. We also show the abundance ratios and the metallicity distribution functions of the Galactic bulge, halo, and thick disk. Our results suggest that the formation timescale of the thick disk is $1Y3 Gyr.

Abundance ratios in the hot ISM of elliptical galaxies

“…Fig. 2 in Kobayashi et al 2006). If we were to extrapolate this trend and adopt 70 M as the upper mass limit for the IMF in the models, the predicted [O, Mg/Fe] ratios in the hot ISM might increase by ∼0.1 dex, but [Fe/H] would remain unaffected.…”

“…3. For SNeII, we use the yields of Kobayashi et al (2006) for the solar composition in the fiducial case (K002, hereafter).…”

Tracing the evolution of the Galactic bulge with chemodynamical modelling of alpha-elements

“…Similarly to oxygen, magnesium is mainly produced during the hydrostatic nuclear burning phases of SNII progenitors (WW95; Kobayashi et al 2006). However, even for the case of an archetypical α element such as magnesium, the nucleosynthesis prescription should take into account the incompleteness of the reaction network and uncertainties in the nuclear physics and the locus where the element is produced.…”

Are ancient dwarf satellites the building blocks of the Galactic halo?

“…For Type Ia supernova (SNe Ia), the adopted nucleosynthesis prescriptions are from Iwamoto et al (1999). (ii) For massive stars (M > 8 ), which are the progenitors of either SNe II or HNe, depending on the explosion energy, they assume the metallicity-dependent He, C, N and O stellar yields, as computed with the Geneva stellar evolutionary code, which takes into account the combined effect of mass-loss and rotation (Meynet & Maeder 2002;Hirschi 2005;Hirschi 2007;Ekström et al 2008); for all the elements heavier than oxygen, they assume the up-to-date stellar evolution calculations by Kobayashi et al (2006).…”