Unveiling Galaxy Formation and Cosmic StarFormation History with Dusty Spectrum Energy Distribution Diagnostics

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We analyse the spectral energy distributions (SEDs) of 30 submm galaxies, including EROs and host galaxies of GRBs, by using an evolutionary SED model of starbursts. From the observed UV-submm SEDs, we predict the present-day colours and magnitudes of submm galaxies. And then compare them with the colour- and size-magnitude relation of elliptical galaxies. With the top-heavy IMF, the present-day colours and magnitudes of submm galaxies are found to be consistent with the colour-magnitude relation of elliptical galaxies. We find that the mean present-day magnitude of submm galaxies corresponds to that of $L^A*$ elliptical galaxies. The derived effective radii of less massive submm galaxies are consistent with the observed effective radius of elliptical galaxies, while massive submm galaxies are an order of magnitude smaller than elliptical galaxies with similar luminosity. This suggests that massive submm galaxies consist of multiple starburst regions. Starburst regions in submm galaxies are found to be self-regulated ; i.e.feedback due to supernovae is nearly balanced with the self-gravity of starburst regions. In such systems, how to cease the star formation depends on the large scale gravitational potential by the dark matter halo, rather than the properties of starburst itself. This may be important to cause the colour-magnitude relation of elliptical galaxies.