H-II REGIONS IN SPIRAL GALAXIES - POSITIONS, LUMINOSITY FUNCTION AND DIAMETER DISTRIBUTION

For a sample of 22 spiral galaxies, most of which are in Virgo, we mea sure positions, diameters and relative magnitudes of the H II regions. The diameter frequency integral distribution is found to follow the e xponential law proposed by van den Bergh (1981) with no exceptions. Th e scale diameter, D0, 1) depends on the galactic absolute magnitude wi th the law log(D0) = - 0.123 +/- 0.007 M(B) - 0.33 +/- 0.14, 2) has a tendency to be larger at the periphery than in the inner part of the g alaxy and 3) is systematically larger along the arms than inter-arms. Although with a large dispersion, a cubic relationship between H II re gion luminosity and diameter, consistent with a radiation bounded geom etry, is found for each galaxy. The differential luminosity function d istribution is described hy a power law with index in the range (1.3 l ess-than-or-equal-to alpha less-than-or-equal-to 2.4) and a mean index [alpha] = 1.8 +/- 0.3 in agreement with previous works.The index alph a is found to depend on the morphological type of the galaxy being ste eper for early than late-type spirals. It sensibly changes if arm and inter-arm distributions are separately considered, but does not depend on the galactocentric distance. The environment characterized by the local density of galaxies does not seem to play a role in the shape of the LF while the diameter scale of H II regions seems to be well defi ned in a narrow region of values at densities rho greater-than-or-equa l-to 1.2 (galaxies Mpc-3) while at lower density the scale diameter sh ows large fluctuations.