  We analyse the spectral energy distributions (SEDs) of 23 submm galaxies and
3 ISO-detected EROs, all of which have the spectroscopic redshifts, by using an
evolutionary SED model of starbursts. This SED model allows us to investigate
intrinsic properties of starbursts, such as the starburst age and the mean
stellar metallicity, as it takes into account the chemical evolution. Also, the
intrinsic size of the starburst region is estimated from observed SEDs. Using
this SED model, we predict colour, magnitude, and size of present-day
descendants of submm galaxies, and derive scaling relations, such as the
present-day colour-magnitude and size-magnitude relations. We argue that submm
galaxies are the progenitors of present-day elliptical galaxies, provided that
the initial mass function (IMF) of submm galaxies is slightly flatter than the
Salpeter IMF. In this case, we find that 1) the mean present-day magnitude of
submm galaxies is similar to that of L* elliptical galaxies, 2) the present-day
colour-magnitude relation is consistent with that of elliptical galaxies, 3)
the present-day size-magnitude relation of elliptical galaxies can be
reproduced if massive submm galaxies consist of multiple starburst regions. We
estimate the effect of feedback in submm galaxies as a function of starburst
age. It is found that starburst regions in submm galaxies are likely to be
self-regulated; i.e. the effect of feedback is nearly balanced with the
self-gravity of starburst regions.
