Statistics and properties of emission-line regions in the local volume dwarf galaxies

Abstract

ABSTRACT We used the H α images from a large sample of nearby late-type dwarf galaxies to investigate properties of their emission structure. The sample consists of 300 galaxies of the irregular (Irr), Magellanic irregular (Im), blue compact dwarf (BCD), and transition (Tr) types situated within a distance of 11 Mpc. In each galaxy, we indicated the number of compact H ii regions, the presence of bubble-like or filament-like structures, the presence of a faint diffuse emission, and a sign of the global burst. The larger the luminosity of a galaxy, the greater number of compact H ii sources in it. The integral and specific star formation rates (SFRs) of the dwarf increase steeply with the increase of the number of H ii regions showing the evidence of the epidemic character of the star formation process. The dwarf galaxies with emission-line bubbles, or filaments, or signs of the global star formation burst have approximately the same hydrogen-mass-to-luminosity ratio as that of the whole sample objects. However, their mean SFR is significantly higher than that of other galaxies in the sample. Emission bubble-like structures are found in the nearby dwarfs with a frequency of one case per four to five galaxies. Their linear diameters are close to those expected for supernova remnants. The mean specific SFR for the nearby late-type dwarfs is close to the Hubble parameter, H0 = −10.14 dex (yr)−1, consistent with the sluggish cosmic star formation history of galaxies of this kind.