The inverse of the survey volume as a function of H I mass is indicated by the thin line in the upper panel of Fig. 1. The curve indicates the upper limit to the space density of intergalactic H I clouds without stars as a function of H I mass. The solid dots in Fig. This function is represented by the fat solid line, using , a faint end slope and a normalization , which is a satisfactory fit to the points. The parameters of this fit agree quite well with those of optical luminosity functions.
Thin line indicates again the sensitivity of the survey.
This function is plotted in Fig. 2. The fat solid line indicates the converted best fit H I mass function, the thin line represents the sensitivity limits. The distribution function clearly illustrates that the integral H I mass density is dominated by high mass galaxies, which are galaxies. From this figure we derive that or , with a statistical error of . This implies that there is not much neutral gas hidden in objects like LSB galaxies or intergalactic clouds that are missed by optical surveys.