Comparison of the Hα equivalent width of HII regions in a flocculent and a grand-design galaxy:: Possible evidence for initial mass function variations

We present here a study of the H alpha equivalent widths of the flocculent galaxy NGC 4395 and the grand-design galaxy NGC 5457. A difference between the mean values of the H alpha equivalent widths for the two galaxies has been found. Several hypotheses are presented in order to explain this difference: differences in age, metallicity, star formation rate, photon leakage, and initial mass function. Various tests and Monte Carlo models are used to find out the most probable cause of this difference. The results show that the possible cause for the difference could be a variation in the initial mass function. This difference is such that it seems to favor a fraction of more massive stars in the grand-design galaxy when compared with the flocculent galaxy. This could be due to a change of the environmental conditions due to a density wave.