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

We compute the baryonic mass function, psi(S)(M-b)d log M-b, Of disc galaxi es using the luminosity functions and baryonic mass-to-light ratios reliabl e for this goal. On scales from 10(8) M. to 10(11) M. this function is feat ureless, psi(S) proportional to M-b(-1/2). Outside this mass range psi(S) i s a strong inverse function of Mb The contributions to the baryon density O mega(b)(S) from objects of different mass indicate that spirals have a char acteristic mass scale at M-b(circle times) similar or equal to 2 X 10(11) M ., around which more than 50 per cent of the total baryonic mass is concent rated. The integral value, Omega(b)(S) = (1.4 +/- 0.2) x 10(-3), confirms, to a higher accuracy, previous evidence that the fraction of BBN baryons lo cked in disc galaxies is negligible and matches that of high-z damped Ly al pha systems (DLAs). We investigate the scenario where DLAs are the progenit ors of present-day spirals, and find a simple relationship between their ma sses and HI column densities by which the DLA mass function closely matches that of spiral discs.