Chemical and Photometric Evolution of Galaxies with Periodic Star Formation - Ellipticals and Irregulars

A new galactic wind model for ellipticals is presented in which a periodic cycle of the star formation and the wind occurs in giant elliptical galaxies after an initial wind. The model explains the paucity of gas in most ellipticals and predicts a significant contribution of intermediate-age stars into the present day V-flux luminosity. Evolutionary models are computed for irregulars and blue compact dwarfs. Neither the continuous star formation model nor the composite star-burst model can consistently explain observed properties such as metallicity, gas mass-to-luminosity ratio, UBV colors, and a lack of red irregulars. A time flattening initial mass function model with a few star-bursts is suggested as the most plausible star formation history.