Galaxies, chemical evolution

Abundance gradients in disk galaxies constitute one of the more important observational constraints for models of galaxy chemical evolution. As a matter of fact, abundance gradients were first recognized to exist in external galaxies, where radial trends of emission line ratios were noted as far back as in the fourties (Aller 1942) and were attributed to abundance gradients in the early seventies (Searle 1971, Shields 1974). 

The studies of other elements in metal-rich planet-host stars is also giving important information about the chemical evolution of the Galaxy. 

As a consequence chemical abundances in PNe are of primary importance for the chemical evolution of spiral galaxies, including our own and related topics. 

Recent observations of the HF (1-0) R9 line at 2.3 /tm with the Phoenix spectrograph on the Gemini-South telescope has opened a new window that sheds light on understanding the chemical evolution of fluorine and the nuclear processes that produce this element. Until recently, only a small number of observations of fluorine were available and the trend of fluorine abundances with metallicity had yet to be probed in the Galaxy. 

The analysis of bright nebular emission lines of Hu regions has been the most frequent approach to modeling chemical evolution of more distant galaxies to... 

The most metal-rich stars in dwarf spheroidals (dSph) have been shown to have significantly lower even-Z abundance ratios than stars of similar metallicity in the Milky Way (MW). In addition, the most metal-rich dSph stars are dominated by an s-process abundance pattern in comparison to stars of similar metallicity in the MW. This has been interpreted as excessive contamination by Type la super-novae (SN) and asymptotic giant branch (AGB) stars ( Bonifacio et al. 2000, Shetrone et al. 2001, Smecker-Hane McWilliam 2002). By comparing these results to MW chemical evolution, Lanfranchi Matteucci (2003) conclude that the dSph galaxies have had a slower star formation rate than the MW (Lanfranchi Matteucci 2003). This slow star formation, when combined with an efficient galactic wind, allows the contribution of Type la SN and AGB stars to be incorporated into the ISM before the Type II SN can bring the metallicity up to MW thick disk metallicities. 

Recent abundance ratio work in this field falls into two categories. The first category has been investigations into aspects of metal-poor AGB and Type la SN yields and their relationship to the chemical evolution in the dSph galaxies, e.g. McWilliam et al. (2003), Venn et al. (2004), McWilliam Smecker-Hane (2005). In these works the abundances of specific elements are compared to... 

The Composition of the Sagittarius Dwarf Spheroidal Galaxy and Implications for Nucleosynthesis and Chemical Evolution... 

Abstract. We present metallicities for 487 red giants in the Carina dwarf spheroidal (dSph) galaxy that were obtained from FLAMES low-resolution Ca triplet (CaT) spectroscopy. We find a mean [Fe/H] of —1.91dex with an intrinsic dispersion of 0.25 dex, whereas the full spread in metallicities is at least one dex. The analysis of the radial distribution of metallicities reveals that an excess of metal poor stars resides in a region of larger axis distances. These results can constrain evolutionary models and are discussed in the context of chemical evolution in the Carina dSph. 

The accretion history of a parent galaxy is constructed using a semi-analytical code. The full phase-space evolution during each accretion event is then followed separately with numerical simulations [2]. Star-formation and chemical evolution models are implemented within each satellite. The star formation prescription matches the number and luminosity of present-day galaxies in the Local Group, whereas the chemical evolution model takes into account the metal enrichment of successive stellar populations as well as feedback processes. Below we present results of a sample of four such simulated galaxy halos, denoted as Halos HI, H2, H3 and H4. 

Massive stars play a key role in the spectral evolution of galaxies, they are also the progenitors of Wo I f Rayet (WR) stars, supernovae and y-ray bursts. They are the main agents of nucleosynthesis driving the chemical evolution of galaxies. The relative numbers of the various kinds of massive stars (blue, red supergiants, WR stars), their properties and nucleosynthesis very much depend on mass loss and rotation, as well as on the interaction of these two effects. 

Abstract. We recall the emergence of the 3He problem , its currently accepted solution, and we summarize the presently available constraints on models of stellar nucleosynthesis and studies of Galactic chemical evolution from observations of the He isotopic ratio in the Galaxy. 

We present chemical evolution models for NGC 6822 computed with five fixed parameters, all constrained by observations, and only a free parameter, related with galactic winds. The fixed parameters are i) the infall history that has produced NGC 6822 is derived from its rotation curve and a cosmological model ii) the star formation history of the whole galaxy based on star formation histories for 8 zones inferred from H-R diagrams iii) the IMF, the stellar yields, and the percentage of Type la SNe progenitors are the same than those that reproduce the chemical history of the Solar Vicinity and the Galactic disk. 

To put together a model for the chemical evolution of galaxies, one needs the... 

Numerical modelling of the chemical evolution of the Milky Way and/or similar disk galaxies, taking into account dynamical effects, was pioneered by Larson (1976) and Tinsley and Larson (1978). Because of many uncertainties in the details... 

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