We present an analysis of the spectral energy distribution (SED) ofsub-millimeter detected galaxies (SMGs) that allows us, through SED evolutionmodels that take into account dust and chemical evolution, to investigate theintrinsic properties of the associated starbursts, such as the starburst age andthe mean stellar rnetallicity. We argue that SMGs are the progenitor of present-day elliptical galaxies, provided that the initial mass function (IMF) in SMGs isslightly flatter than the Salpeter IMF. This picture is supported by the followingfindings: 1) the mean predicted present-day magnitude of SMGs is similar to thatof L~*elliptical galaxies, 2) the predicted present-day color-magnitude relation ofthe SMGs is consistent with that of elliptical galaxies, 3) the predicted present-day magnitude-size relation of elliptical galaxies can be reproduced if massiveSMGs consist of multiple starburst regions. Our analysis also found that themassive SMGs tend to show ages > 8 Gyr while some of the less-massive onescan be relatively young < 8 Gyr, which is similar to the down-sizing that isobserved in galaxy formation.
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