Mid-infrared imaging and spectrophotometry of N 66 in the SMC with ISOCAM

We present observations with the mid-infrared camera ISOCAM on board the In frared Space Observatory of the major star-forming region N 66 in the Small Magellanic Cloud (SMC) and of its surroundings. These observations were pe rformed with broad filters and Circular Variable Filters giving a spectral resolution of about 40. In addition, CO(2-1) data are presented, allowing u s to identify and study how hot dust relates with the different phases of t he Interstellar Medium (ISM) present in N66. The spectra are dominated by t he strong emission of fine-structure line. Monochromatic maps have been mad e in the [Ne III] 15.6 mum and [S rv] 10.5 mum line. There are significant differences between their distributions, due to the effects of density and of shocks. Aromatic Infrared Bands (AIBs) are seen at various places in the field but they are generally faint. They exhibit a variety of shapes and r elative intensities, suggesting that a diversity of carbonaceous materials are present. Silicate emission is also clearly visible in the central conde nsation and in a few others and emission from hot small grains (Very Small Grains, VSGs) longward of 10 mum is present in the whole region. All these dust components are heated by the very strong far-UV radiation of the many young, massive stars contained in the region. The interstellar radiation fi eld (ISRF) at 1600 Angstrom is greater than or equal to 10(5) times the ISR F of the solar neighborhood in the peaks of mid-infrared emission. The rela tive contributions of these components (AIB carriers, VSGs and silicate gra ins) to the mid-infrared spectra seem to depend on the intensity and the ha rdness of the far-UV field. In general the 15/6.75 mum intensity ratio is h igher than in relatively quiescent galactic regions (Cesarsky et al. 1996a, Abergel et al. 1996) but it is not as high as expected for a linear increa se with ISRF We interpret this behavior as due to the destruction of both A IBs carriers and VSGs in a very high ISRF Finally several stars have been d etected at 6.75 mum Two are red supergiants; the ether stars are blue and t he IR emission is due to circumstellar matter or to interstellar matter hea ted by the star.