A census of metals at high and low redshifts and the connection between submillimetre sources and spheroid formation

Deep surveys in many wavebands have shown that the rate at which stars were forming was at least a factor of 10 higher at z > 1 than today. Heavy elements (metals) are produced by stars, and the star formation history deduced by these surveys implies that a significant fraction of metals in the universe today should already exist at z~2-3. However, only 10% of the total metals expected to exist at this epoch have so far been accounted for (in DLAs and the Lyman forest). In this paper, we use the results of submillimetre surveys of the local and high redshift universe to show that there was much more dust in galaxies in the past. We find that a large proportion of the missing metals are traced by this dust, bringing the metals implied from the star formation history and observations into agreement. We also show that the observed distribution of dust masses at high redshift can be reproduced remarkably well by a simple model for the evolution of dust in spheroids, suggesting that the descendants of the dusty galaxies found in the deep submm surveys are the relatively dust-free spiral bulges and ellipticals in the universe today.