Chemical Evolution of the Galactic Halo(Proceedings of Japan-France Seminar on Chemical Evolution of Galaxies with Active Star Formation)

A three-zone model of chemical evolution of our Galaxy is proposed to explain overall distribution of the metallicity in the Galaxy. The metallicity enrichment is strongly affected by gas flow from the outer part to the inner part of the protogalaxy during the contraction of proto-galactic gas cloud. The population in the outer halo is formed in the free-fall phase of the initial collapse of the protogalaxy, and the inner halo population is formed during the following quasistatic contraction, while the disk population is formed from the gas fallen from the halo regions