The 5 Gyr evolution of sub-M galaxies

We gathered two complete samples of M-AB(r) < -18 (M-star > 10(9)M(circle dot)) galaxies, which are representative of the present-day galaxies and their counterparts at 5 Gyr ago. We analysed their 2D luminosity profiles and carefully decomposed them into bulges, bars and discs. This was done in a very consistent way at the two epochs, by using the same image quality and same (red) filters at rest. We classified them into elliptical, lenticular, spiral and peculiar galaxies on the basis of a morphological decision tree. We found that at z = 0, sub-M* (10(9)M(circle dot) < M-star < 1.5 x 10(10)M(circle dot)) galaxies follow a similar Hubble sequence compared to their massive counterparts, though with a considerable larger number of (1) peculiar galaxies and (2) low surface brightness galaxies. These trends persist in the z similar to 0.5 sample, suggesting that sub-M* galaxies have not reached yet a virialized state, conversely to their more massive counterparts. The fraction of peculiar galaxies is always high, consistent with a hierarchical scenario in which minor mergers could have played a more important role for sub-M* galaxies than for more massive galaxies. Interestingly, we also discovered that more than 10 per cent of the sub-M* galaxies at z = 0.5 are low surface brightness galaxies with clumpy and perturbed features that suggest merging. Even more enigmatic is the fact that their disc scalelengths are comparable to that of M31, while their stellar masses are similar to that of the LMC.