The dynamics and chemical composition of giant extragalactic H II regions

The dynamic and chemical composition of giant extragalactic H II regions is analyzed, and the data pertaining to H-beta luminosities, linear diameters and emission-line profile widths are correlated. Results show that giant H II regions display the same relations between size, luminosity, and velocity dispersion as noted in gravitationally bound stellar systems. The observed emission-line profile widths represent the velocity dispersion of ionized gas clouds moving in the overall gravitational potential of gas and stars, and the integrated luminosities of H II regions are specified by the velocity dispersions and metallicities. It is suggested that the ionizing flux per unit total mass of a burst of star formation is decreasing with increasing metal abundance.