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Register a new userEffects of the galactic winds on the stellar metallicity distribution of dwarf spheroidal galaxies
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Gustavo A. Lanfranchi
Publication date
2007
fields
Physics
and research's language is
English
Authors
Gustavo A. Lanfranchi
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To study the effects of galactic winds on the stellar metallicity distributions and on the evolution of Draco and Ursa Minor dwarf spheroidal galaxies, we compared the predictions of several chemical evolution models, adopting different prescriptions for the galactic winds, with the photometrically-derived stellar metallicity distributions of both galaxies. The chemical evolution models for Draco and Ursa Minor, which are able to reproduce several observational features of these two galaxies, such as the several abundance ratios, take up-to-date nucleosynthesis into account for intermediate-mass stars and supernovae of both types, as well as the effect of these objects on the energetics of the systems. For both galaxies, the model that best fits the data contains an intense continuous galactic wind, occurring at a rate proportional to the star formation rate. Models with a wind rate assumed to be proportional only to the supernova rate also reproduce the observed SMD, but do not match the gas mass, whereas the models with no galactic winds fail to reproduce the observed SMDs. In the case of Ursa Minor, the same model as in previous works reproduces the observed distribution very well with no need to modify the main parameters of the model. The model for Draco, on the other hand, is slightly modified. The observed SMD requires a model with a lower supernova type Ia thermalization efficiency ($eta_{SNeIa}$ = 0.5 instead of $eta_{SNeIa}$ = 1.0) in order to delay the galactic wind, whereas all the other parameters are kept the same. The model results, compared to observations, strongly suggest that intense and continuous galactic winds play a very important role in the evolution of local dSphs.
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Recent observations show that the number of stars with very low metallicities in the dwarf spheroidal satellites of the Milky Way is low, despite the low average metallicities of stars in these systems. We undertake numerical simulations of star formation and metal enrichment of dwarf galaxies in order to verify whether this result can be reproduced with standard assumptions. The answer is likely to be negative, unless some selection bias against very low metallicity stars is present in the observations.
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