SIMBAD references

We discuss the possible origin of the radial truncations in stellar discs, using measurements that we presented in an earlier paper. A tentative correlation is found with the de-projected face-on central surface brightness; lower surface brightness discs tend to have a smaller truncation radius in units of scalelength. This and our earlier finding that in smaller spirals the truncation tends to occur at a larger number of scalelengths are best reproduced when the truncation is caused by a constant gas-density threshold on star formation.