The chemical evolution of the solar neighborhood. II - The age-metallicity relation and the history of star formation in the galactic disk

The age-metallicity relation for the disk in the neighborhood of the sun is derived from four-color and H-beta photometry of a large sample of southern F dwarfs, analyzed in combination with theoretical isochrones. It is found that the mean metallicity of the disk increased by about a factor of five between 12 and 5 billion years ago and has increased only slightly since then. The star formation rate (SFR) for the disk as a function of time is obtained from the number count data, taking into account stellar evolution and the disk scale height corrections. The SFR which produces a metallicity distribution for the F stars consistent with the G dwarf data is one where the SFR has remained relatively constant over the lifetime of the disk. It is concluded that the disk has collapsed by about a factor of 6 perpendicular to the galactic plane during its lifetime, most of the collapse occurring 13 to 7 billion years ago.