Infrared observations and stellar populations modeling of starburst galaxies

Abstract

We present a study of a sample of starburst galaxies. The systems chosen for study range in age and strength. We have obtained high-quality infrared spectroscopy and imaging of 18 starburst galaxies and 4 early-type galaxies as a comparison sample of an old stellar population. The spectra consist of high-resolution data (R ∼ 3000) in the H (1.65μm) and K (2.2μm) bands and, in a few cases, the J (1.25μm) band; most of the J-band spectra were obtained at a resolution of 800. We obtained broadband images of all the galaxies in the J, H, and K bands, as well as narrowband images of several of the galaxies in the (1.0)S(1) line of H₂ and in Brγ. We use these data and data from the literature to constrain models of the nuclear starbursts for these galaxies. The high sensitivity and resolution of the spectra plus the use of a long slit allows us to derive kinematic properties of the nuclear region in addition to other constraints on the starburst population, such as ionizing flux and CO index. We compare the properties of these galaxies and suggest that a burst of star formation can account for the galaxy properties and that the range of properties observed is derived from a range of burst ages and strengths. Our high-quality data allow us to examine the properties of the (Fe II) and H₂ emission regions. We measure, for the first time, the density in the (Fe II) -emitting region of a starburst galaxy and find that this density is consistent with the origin of this emission in supernova remnants. We find, in contrast to earlier studies, that fluorescence plays a large role in the H₂ emission of some starburst galaxies.