H II regions in NGC 628. III - H-alpha luminosities and the luminosity function

A complete photometric mapping of NGC 628 in the light of H-alpha is used to measure the luminosities of 593 H II regions. Isophotometry of a few individual objects is used to derive the basic properties of the H II region population. Both the luminosity and the diameter functions are well represented by steep power laws. The H II region luminosity function is largely independent of radius in NGC 628 and is the same in or out of spiral arms. There exists a marked difference, however, between the populations in or out of spiral arms. The H II region function is used to derive the approximate form of the OB associated mass function.