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Iron is an abundant refractory element; however, it is highly depleted from the gas phase of the interstellar medium of galaxies as a result of condensation into dust grains. Forbidden line emission from low ionization states of iron is greatly enhanced behind hydrodynamic shock fronts where sputtering processes volatilize the grains such that the gas phase abundance of iron can reach near-solar values. This enhancement can provide a new sensitive measure of the supernova content of galaxies.
Supernovae activity can produce widely distributed [Fe~II] emission as a result of in situ grain destruction over large distances and by direct enrichment of their environment via decay of $\rm ^{56}Ni$. As a result, one expects galactic nuclei undergoing prodigious massive star formation to be characterized by high [Fe~II] luminosity relative to normal galaxies. This phenomena suggests that infrared [Fe~II] imaging can provide a new technique to: [a] compare the supernova activity of galaxies via [Fe~II] luminosities derived from high spatial resolution emission line images, [b] compare the spatial distribution of supernova ejecta and associated grain processing shocks to the spatial distribution of current star formation revealed by H recombination line images, and [c] delineate individual young supernova remnants in near-by galaxies.
We display high spatial ($\simeq 40$~pc) and medium spectral ($\simeq 400$~km~s$^{-1}$) resolution [Fe~II]1.644~$\mu$m images of M82 obtained with the National Air and Space Museum J/H-band Fabry-Perot coupled to the Third Generation Rochester Infrared Camera at the Wyoming Infrared Observatory (WIRO). The spatial relationship of the extended [Fe~II] emission to other emission components in M82 is displayed and discussed.
This work was supported by the Smithsonian Institution Scholarly Studies Program, NSF grant AST93-57392, and the Office of Naval Research.
