Near-Infrared Integral Field Spectroscopy of Star-forming Galaxies

The Palomar Integral Field Spectrograph was used to probe a variety of environments in nine nearby galaxies that span a range of morphological types, luminosities, metallicities, and infrared-to-blue ratios. For the first time, near-infrared spectroscopy was obtained for nuclear or bright H II regions in star-forming galaxies over two spatial dimensions (5!!7 x 10!!0) in the [Fe II] (1.257 mu m), [Fe II] (1.644 mu m), Pa beta (1.282 mu m), H sub(2) (2.122 mu m), and Brgamma (2.166 mu m) transition lines. These data yield constraints on various characteristics of the star-forming episodes in these regions, including their strength, maturity, spatial variability, and extinction. The H II regions stand out from the nuclei. Unlike observations of nuclear regions, H II region near- infrared observations do not show a spatial coincidence of the line and continuum emission; the continuum and line maps of H II regions usually show distinct and sometimes spatially separated morphologies. Gauging from Pa beta and Brgamma equivalent widths and luminosities, the H II regions have younger episodes of star formation than the nuclei and more intense radiation fields. Near-infrared line ratio diagnostics suggest that H II regions have "purer" starbursting properties. The correlation between ionizing photon density and mid-infrared color is consistent with the star formation activity level being higher for H II regions than for nuclei. And though the interpretation is complicated, on a purely empirical basis the H II regions show lower Fe super(1+) abundances than nuclei by an order of magnitude.