2005A&A...431..235R

We present an analysis of the integrated Hα emission line profiles for the HII region population of the spiral galaxies NGC 1530, NGC 6951 and NGC 3359. We show that ∼70% of the line profiles show two or three Gaussian components. The relations between the luminosity (logL_Hα) and non-thermal line width (logσ_nt) for the HII regions of the three galaxies are studied and compared with the relation found taken all the HII regions of the three galaxies as a single distribution. In all of these distributions we find a lower envelope in logσ_nt. A clearer envelope in σ_nt is found when only those HII regions with σ_nt>σ_s(13km/s) are considered, where σ_s is a canonical estimate of the sound speed in the interestellar medium. The linear fit for the envelope is log L_Hα=(36.8±0.7)+(2.0±0.5) log σ_nt where the Hα luminosity of the region is taken directly from a photometric HII region catalogue. When the Hα luminosity used instead is that fraction of the HII region luminosity, corresponding to the principal velocity component, i.e. to the turbulent non-expanding contribution, the linear fit is logL_Hα=(36.8±0.6)+(2.0±0.5)logσ_nt, i.e. unchanged but slightly tighter. The masses of the HII regions on the envelope using the virial theorem and the mass estimates from the Hα luminosity are comparable, which offers evidence that the HII regions on the envelope are virialized systems, while the remaining regions, the majority, are not in virial equilibrium.