The role of environment in the evolution of dwarf irregular galaxies: a comparison of UBVR and Hα photometry

The star formation properties of 33 dwarf irregular galaxies that reside in differing local and global environments are investigated through UBVR and Hα photometry. Local environment is defined by the local galaxy number density, where high indicates at least one neighbour within 200 kpc and low indicates no neighbours within 1 Mpc. Global environment is classified as either field or group/cluster. Dwarf irregular galaxies are ideal candidates for a study on the role of environment in galaxy evolution due to their shallow gravitational potentials. Galaxies in local high-density environments are found to have brighter central and effective surface brightnesses, while those in global high-density environments have brighter absolute magnitudes, central and effective surface brightnesses, and higher star formation rates. However, no difference is seen among the different environments when considering star formation rates normalized by H i mass. Sérsic profiles were fit to the V- and R-band surface brightness profiles of the galaxies. No correlation exists between structural characteristics and environment. Most optical properties of dwarf irregular galaxies were found to be independent of environment, indicating that cluster membership and proximity to a neighbouring galaxy have no systematic long-term effects on the evolution of the objects in this study. Either environmental effects on dwarf galaxies are too sensitive to specific conditions for environmental trends to occur, or environmental influences result in a morphological evolution (e.g. dwarf irregular evolves to dwarf elliptical), which would not be apparent in a sample of only one morphological type.