Star formation history and stellar metallicity distribution in a cold dark matter universe

We study star formation history and stellar metallicity distribution in galaxies in a Lambda cold dark matter universe using a hydrodynamic cosmological simulation. Our model predicts a star formation rate declining in time exponentially from an early epoch to the present on a timescale of 6 Gyr, which is consistent with the empirical Madau plot with modest dust obscuration. Star formation in L* galaxies continues intermittently to the present, also with an exponentially declining rate on a similar timescale, whereas in small galaxies star formation ceases at an early epoch. The mean age of the extant stars decreases only slowly with increasing redshift and exceeds 1 Gyr at z = 3. Normal galaxies contain stars with a wide range of metallicity and age: stars formed at z < 1 have metallicity of 0.1-1.0 Z(.), while old stars take a wide range of values, from 10(-6) to 3.0 Z(.). The mean metallicity of normal galaxies is in the range 0.1-1.0 Z(.). Dwarf galaxies that contain only old stars have a wide range of mean metallicity (10(-4) to 1.0 Z(.)), but on average they are metal-deDcient compared with normal galaxies.