Abstract
A series of direct photographs are analyzed of the nuclear region of M82. These have being obtained under excellent seeing conditions (∼ 0.5"). The observations were carried out with an S-1 image tube camera attached to the 3 m telescope at Lick Observatory (plate scale 4"/mm). Four band passes were defined by the spectral response of the photocathode along with filters chosen in such a manner as to have dominating from [SIII] (λλ9069,9530 A), He (λ10830 A), [S111] + IR continuum and blue continuum (λ4000-5000 A). An additional panchromatic image of the full S-1 response was also obtained. These photographs show bright knots (Mv ∼-15) many of them not previously detected or resolved. Some of those might be identified with ionized regions or superclusters, and others as by-products of the irregular structure of the extinction due to the presence of dust clouds. The extinction reaching Av ∼ 15-20 magnitudes in certain areas. The luminosity of the superclusters requires the presence of up to 10^3-10^4 massive O and B stars per cluster, hence they should provide most of the ionizing radiation in the central region of M82. A comparison of our data with radio continuum maps at 6-cm show little correspondence. However we have detected a small condensation coincident with the position of the strongest unresolved radio source. The latter showing non-thermal radiation at radio- wavelengths. The possible role of such a source in ionizing the central region is not clear. Comparison of X-ray maps (0.2-3.5 Kev) with our pictures in [S111] and He λ10830 A, points out that the X-ray radiation is essentially mapping the ionized matter.
