Massive stellar content of giant H II regions in M33 and M101 ¹

Far-ultraviolet (900-1200 Å) spectral synthesis of nine giant extragalactic H II regions in M33 and M101 is performed to study their massive stellar content. Several parameters are quantified, predicted, and compared to the literature: age, stellar mass, initial mass function (IMF) slope, number of O-type and Wolf-Rayet stars, and Hα and 5500 Å continuum fluxes. The results of this particular technique are consistent with other methods and observations. This work shows that a total stellar mass of a few 10 ₃ M _⊙ is needed to populate the IMF bins well enough at high masses to obtain accurate results from the spectral synthesis technique in the far-ultraviolet. A flat IMF slope seems to characterize better the stellar line profiles of these objects, which is likely the first sign of a small number statistics effect on the IMF. Finally, the H II region NGC 5461 is identified as a good candidate for hosting a second generation of stars, not yet seen at far-ultraviolet wavelengths.