SIMBAD references

Observed variations in the H II region luminosity function (H II LF) seen in spiral arm versus interarm regions, and different galactic Hubble type, can be explained simply by evolutionary effects and maximum number of ionizing stars per cluster. We present Monte Carlo simulations of the H II LF, drawing the number of ionizing stars (N_*) from a power-law distribution of constant slope, and the stellar masses from a Salpeter initial mass function with an upper mass limit of 100 M_☉. We investigate the evolution of the H II LF, as determined by stellar main-sequence lifetimes and ionizing luminosities, for a single-burst case and continuous creation of the nebular population. Shallower H II LF slopes measured for the arms of spiral galaxies can be explained as a composite slope, expected for a zero-age burst population, whereas the interarm regions tend to be dominated by evolved rich clusters described by a single, steeper slope. Steeper slopes in earlier-type galaxies can be explained simply by a lower maximum N_* cutoff found for the parent OB associations. The form of the H II LF can reveal features of the most recent (≲10 Myr) star formation history in nearby galaxies.