The baryonic mass function of spiral galaxies: clues to galaxy formation

We compute the baryonic mass function, ψ S ( M b ) d log  M b , of disc galaxies using the luminosity functions and baryonic mass‐to‐light ratios reliable for this goal. On scales from 10 8  M ⊙ to 10 11  M ⊙ this function is featureless, . Outside this mass range ψ S is a strong inverse function of M b . The contributions to the baryon density from objects of different mass indicate that spirals have a characteristic mass scale at , around which more than 50 per cent of the total baryonic mass is concentrated. The integral value, , confirms, to a higher accuracy, previous evidence that the fraction of BBN baryons locked in disc galaxies is negligible and matches that of high‐ z damped Ly α systems (DLAs). We investigate the scenario where DLAs are the progenitors of present‐day spirals, and find a simple relationship between their masses and H  i column densities by which the DLA mass function closely matches that of spiral discs.