1995A&A...295..335C

This paper aims to see whether a generalized Schmidt star formation law is consistent with observations in the light of a closed, comoving model of chemical evolution, where two main phases occurred: contraction (extended component) and equilibrium (flat component). It is shown that the empirical relation between present-day gas mass which is being turned into stars and gas mass, {dot}(M)_ga∝M_ga, i.e. a linear correlation between the model present-day star formation rate and gas mass fraction, C_D∝µ_a, yields a connection between the ratio of contraction time to age, T_c/T, and µ_a. The comparison between model predictions and observations leads to the following main conclusions: (i) models where star formation obeys a pure Schmidt law cannot fit the whole set of observations; (ii) if we demand (in dealing with an averaged C_D/µ_a)T_c/T>0 for all the galaxies and T_c/T<0.5 for at least a fraction of large-mass (M>10¹¹M_☉) galaxies of the sample considered, then a generalized Schmidt star formation law with an exponent n≃1 is preferred in respect to n≃2; (iii) if contraction and equilibrium phase were characterized by different star formation rates and mass spectra, then a correlation exists between present-day metal content and gas mass fraction. Thus a generalized Schmidt star formation law with exponent n≃1 appears to be consistent with observations.