Origins and interpretation of the tridimensional kinematical disorder in H ii regions

Classical spectro‐interferometry allowed us to obtain a large‐scale H α survey of the central portions of the late‐type Sc galaxy M33. A series of 28 small‐to‐intermediate size H  ii regions, kinematically dominated by Champagne flows, quiescent wind effects, potentially embedded globules and filaments, and photoablation flows, are identified and delimited. The main goal of this work is to compare and check for an eventual correlation between two statistical parameters obtained for each targeted object, namely the standard deviation of the velocity centroid distribution ( σ c ) and the mean non‐thermal linewidth ( 〈σ i , kin 〉 ). These parameters, by definition, allow for a comparison between the kinematical disorder on the plane of the sky and along the line‐of‐sight. The slope of the σ c versus 〈σ i , kin 〉 diagram, approaching unity, indicates that variations of the kinematical disorder are roughly equivalent on all spatial axes. H  ii regions should therefore be regarded as strictly tridimensional objects. We attempt to reproduce the observed relation using non‐turbulent, hydrodynamical models of expanding H  ii regions. Simulations indicate that the two parameters are generally correlated, as observed, in a monotonically increasing trend although the areas populated in the theoretical σ c −〈σ i , kin 〉 space diagram do not match the observations. A certain reconciliation between models and observations is reached if one allows turbulent motions to have a sizeable kinematical impact in the ionized medium, i.e. confirming that all H  ii regions in the survey have a strong turbulent component. This could apply to all optical nebulae hence in agreement with high Reynolds numbers typically found in the ionized interstellar medium. A photometric investigation of bright stars found in our nebula sample indicates that Champagne‐like objects coexist with wind‐blown bubbles in the σ c versus 〈σ i , kin 〉 diagram. This suggests that objects characterized by multiple Champagne flows and those that are wind‐dominated can develop turbulent velocity motions of comparable amplitudes.