Application of the limit-cycle model to star formation histories in spiralgalaxies: Variation among morphological types

We propose a limit-cycle scenario of star formation history for any morphol ogical type of spiral galaxy. It is known observationally that an early-typ e spiral sample has a wider range of present star formation rate (SFR) than a late-type sample. This tendency is understood in the framework of the li mit-cycle model of the interstellar medium (ISM), in which the SFR changes cyclically in accordance with the temporal variation of the mass fraction o f the three ISM components. When the limit-cycle model of the ISM is applie d, the amplitude of variation of the SFR is expected to change with the sup ernova (SN) rate. Observational evidence indicates that early-type spiral g alaxies should show smaller rates of present SNe than late-type ones. Combi ning this evidence with the limit-cycle model of the ISM, we predict that t he early-type spiral galaxies will show larger amplitudes in their SFR vari ation than the late types. Indeed, this prediction is consistent with the o bserved wider range of the SFR in the early-type sample than in the late-ty pe sample. Thus, in the framework of the limit-cycle model of the ISM, we a re able to interpret the difference in the amplitude of SFR variation among the morphological classes of spiral galaxies.