Present-day scaling relations for submillimetre galaxies: the origin of spheroidal systems

Abstract

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