Integrated Colors of Galaxies of Composite Metallicity
Chemical and photometric properties of galaxies of composite metallicity are studied by using an evolutionary method of population synthesis. We find reasonable consistency between the model and the observation, except for irregular galaxies. Ellipticals, SO’s and spirals are systems large enough to allow a statistical model treatment ignoring spacial and temporary fluctuation. If statistically continuous one-zone picture is applicable, these galaxies are well characterized by the universal initial mass function (IMF) and the simple star formation rate (SFR) per unit gas mass which decreases from ellipticals to late spirals. A wind separates galaxies into two distinct sequences of the gas-poor galaxies and the gasrich ones. High SFR’s induce a supernova (SN) driven galactic wind at t<l Gyr in ellipticals and at 1 Gyr<t< (TG-1) Gyr in SO’s, whereas in early and late spirals the explosion rates of SN are too low to expel the gas from the systems within a galactic age of TG=15 Gyr. It is suggested that the gas-poor galaxies such as ellipticals, dwarf ellipticals, and globular clusters are essentially formed as a one-parameter family of mass and that the Hubble sequence of galaxies should reflect a certain initial correlation between mass and angular momentum of protoclouds.
KeywordsStar Formation Globular Cluster Dwarf Galaxy Star Formation Rate Elliptical Galaxy
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