HIGH-SPATIAL-RESOLUTION FABRY-PEROT IMAGING OF M82 - NEAR-INFRARED RECOMBINATION LINE OBSERVATIONS

We present high spatial resolution (similar to 1 '') and moderate spec tral resolution (gamma 2/Delta gamma similar or equal to 800) Pa beta and Br gamma Fabry-Perot imaging observations of the central kiloparse c of M82. These observations, in conjunction with new near-infrared br oadband imaging observations, are used to examine the extinction towar d the starburst region, the state of the ionized gas, and the nature o f the stellar population. Enhancements in the extinction-sensitive Pa beta/Br gamma flux ratio are found to trace out the molecular lobes se en in CO, supporting the assumption that we are observing a dense toru s surrounding the central stellar clusters and H II regions. Using a n onuniform foreground screen model for the Pa beta/Br gamma flux ratio, the derived extinction toward the starburst region is found to vary f rom A(V) similar or equal to 2 to A(V) similar or equal to 12 mag, sig nificantly smaller than is adopted in most other studies of the stella r population in the starburst region of M82. The extinction-corrected K-magnitude in a 30 '' aperture centered on the nucleus is found to be M(K) = -22.0. This is substantially fainter than previous values adop ted, amounting to as much as a reduction of a factor of similar to 3 i n the intrinsic K luminosity, a difference that substantially weakens the arguments made previously for a low mass-deficient IMF for the sta rburst region of M82. Our recombination line images were used to estim ate separately the contribution to the near-infrared continuum bandpas ses from free-free and free-bound processes and the emission from dust . These sources of emission do not contribute appreciably to the total near-infrared continuum and thus it can confidently be assumed that t his emission is dominated by starlight. In addition, we present narrow -band imaging observations of M82 in the 3.29 mu m unidentified dust f eature. The emission is seen to be well-correlated with the Br gamma e mission. The ratio of the extinction-corrected 3.29 mu m dust feature flux to extinction-corrected Br gamma flux is found to vary from 4.5 t o 15 throughout most of the starburst region, with values greater than 35 near the dynamical center of the galaxy. This variation, along wit h other star formation diagnostics, suggests that the nucleus contains a later-type stellar population and the starburst phenomena is propag ating outward. The ratio of the total far-infrared luminosity to the d ereddened 3.29 mu m feature luminosity is found to be 1340 +/- 260 for M82, significantly smaller than the ratio obtained using the uncorrec ted 3.29 mu m feature flux (1690 +/- 200).