The Origin and Evolution of the Mass-Metallicity Relationship of Galaxies: Results from Cosmological N-Body Simulations

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  • 21 September 2006
Abstract
We examine the origin and evolution of the mass-metallicity (M-Z) relationship for galaxies using high resolution cosmological SPH + N-Body simulations that include a physically motivated description of the effects of supernovae feedback and subsequent metal enrichment. Our simulations allow us to distinguish between two possible sources that contribute to both the origin of the mass-metallicity relationship and to the low chemical yield observed in low galaxy masses: 1) metal loss due to gas outflow, or 2) inefficient star formation at the lowest galaxy masses. Our simulated galaxies are in excellent agreement with the observed M-Z relationship, both at z=0 and z=2. We find that gas mass loss becomes increasingly important at decreasing galaxy masses for our simulations, This mass loss results in a low effective yield for our lowest mass galaxies in good agreement with observational results. By considering all the gas that has ever belonged to a galaxy (back to z=3), we find the metallicity is unchanged from the measured value from cold gas at z=0, while the effective yield increases to an asymptotic value as would be expected in a closed box model. Hence we show that mass loss does not effect the metallicity of the low mass systems, or subsequently the M-Z relation, while the observed low effective yields for low mass systems are mostly due to mass loss. Instead, low star formation efficiencies, regulated by supernovae feedback, are primarily responsible for the M-Z trend. We find that the shape of the M-Z relation is relatively constant with redshift, but that the normalization increases with time. Simulations with no supernovae feedback fail to reproduce the observed trends.

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