2 to 8 micron spectrophotometry of M82

Observations of the central 30 arcsec of the galaxy M82 with 1.5% spectral resolution from 2 to 8 microns are reported. Three emission features broader than the instrument resolution are observed. Hydrogen recombination lines are also observed; they indicate an amount of thermal bremsstrahlung emission equivalent to 0.8 Jy of radio flux at 3.5 mm and provide an estimate of approximately 25 magnitudes for the extinction to the H II region. An upper limit on the 8.99-micron forbidden Ar III line intensity together with the measured forbidden Ar II intensity implies that the excitation of the H II region is extremely low. Comparison of fine-structure lines, including the 8- to 13-micron data of Gillett et al. (1973), with the hydrogen lines shows that argon and neon have approximately their cosmic abundance.