Cosmic metal production and the mean metallicity of the Universe
  By means of detailed chemo-photometric models for elliptical, spiral and irregular galaxies, we evaluate the cosmic history of the production of chemical elements as well as the metal mass density of the present-day universe. We then calculate the mean metal abundances for galaxies of different morphological types, along with the average metallicity of galactic matter in the universe (stars, gas and intergalactic medium). For the average metallicity of galaxies in the local universe, we find Z_gal= 0.0175, i.e. close to the solar value. We find the main metal production in spheroids (ellipticals and bulges) to occur at very early times, implying an early peak in the metal production and a subsequent decrease. On the other hand, the metal production in spirals and irregulars is always increasing with time. We perform a self-consistent census of the baryons and metals in the local universe finding that, while the vast majority of the baryons lies outside galaxies in the inter-galactic medium (IGM), 52 % of the metals (with the exception of the Fe-peak elements) is locked up in stars and in the interstellar medium. We estimate indirectly the amount of baryons which resides in the IGM and we derive its mean Fe abundance, finding a value of X_Fe,IGM=0.05 X_Fe,sun. We believe that this estimate is uncertain by a factor of 2, owing to the normalization of the local luminosity function. This means that the Fe abundance of 0.3 solar inferred from X-ray observations of the hot intra-cluster medium (ICM) is higher than the average Fe abundance of the inter-galactic gas in the field. 
F. Calura, F. Matteucci (DAUT, Trieste)