Infrared Spectroscopy of Blue Dwarf Galaxies

Abstract

We present a survey of the near-infrared emission lines of eight blue dwarf galaxies. These galaxies have advantages for study of the excitation of the interstellar medium by starbursts because the effects are relatively undiluted by the quiescent stellar population, the star formation episodes usually appear to be of short duration, and the effects of metallicity can be examined. Diagnostic tools for the interpretation of [Fe II](1.64) and H2(2.12) emission lines emitted by starburst galaxies are developed and the results are compared with a starburst model. We confirm that the [Fe II](1.64) line is mainly excited in supernova remnants, but the H2 emission appears to arise from a variety of different excitation mechanisms. Many of the galaxies show evidence for a fluorescently excited component of H2. The temperature of the hot stellar population is analyzed by means of the He I(1.70 mu m) emission line and compared with estimates from the [O III]/H beta ratio in the optical and from the mid-infrared fine structure lines. The agreement is reasonably good, although there appears to be a tendency for the temperature to be overestimated by use of the [O III]/H beta ratio.