THE H II REGIONS OF NGC 6822. II. THE LUMINOSITY FUNCTION AND SIZE DISTRIBUTION

Calibrated Hα CCD images of 145 H II regions in the Local Group galaxy NGC 6822 are used to obtain an absolute Hα luminosity function and several versions of diameter distributions. The luminosity function reaches from the most luminous H II region, which has an Hα flux of 4 x 1038^ ergs sec-1^, to the faintest limit yet obtained for an extragalactic H II region population, at a level of 5 x 1034^ ergs sec-1^. We are thus exploring here a portion of the H II region luminosity realm that has hitherto been largely unsampled, except in the solar neighborhood. Most of the H II regions are sufficiently faint to be explained by the excitation of a single early-type star, though some of the faintest are probably segments of diffuse galactic emission. Although the bright end of the luminosity function can be fit satisfactorily to a power law, as found for most spiral galaxies, the curve has a peak at a flux of approximately 1036^ ergs sec-1^, with a shallow decrease in number for fainter H II regions. This behavior results from the fact that the amount of ultraviolet energy released decreases more steeply than the number of stars increases for later-type stars. Three different definitions of sizes are used to explore the properties of the H II region size distribution. As found for other galaxies, the size distribution can be fit by an exponential; the size scale is 33 pc. The fluxes are correlated to the 2.8 power of the diameter, but there is a large intrinsic scatter in this relationship.