Ionized gas velocity dispersion in nearby dwarf galaxies: looking at supersonic turbulent motions★

Abstract

We present the results of an ionized gas turbulent motions study in several nearby dwarf galaxies using a scanning Fabry–Perot interferometer with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). Combining the ‘intensity–velocity dispersion’ diagrams (⁠⁠) with two-dimensional maps of radial velocity dispersion, we found a number of common patterns pointing to the relation between the value of chaotic ionized gas motions and processes of current star formation. In five out of the seven analysed galaxies, we identified expanding shells of ionized gas with diameters of 80–350 pc and kinematic ages of 1–4 Myr. We also demonstrate that the diagrams may be useful for the search of supernova remnants, other small expanding shells or unique stars in nearby galaxies. As an example, a candidate luminous blue variable (LBV) was found in UGC 8508. We propose some additions to the interpretation, previously used by Muñoz-Tuñón et al. to explain the diagrams for giant star formation regions. In the case of dwarf galaxies, a major part of the regions with high velocity dispersion belongs to the diffuse low surface brightness emission, surrounding the star-forming regions. We attribute this to the presence of perturbed low-density gas with high values of turbulent velocities around the giant H ii regions.