1996A&A...308..723I

High-resolution (about 1') maps of the irregular galaxy NGC 6822 show that about half the far-infrared emission arises in discrete sources with sizes less than 400 pc, three of which are associated with the brightest HII regions. Two equally bright infrared sources have no such counterpart. Dust temperatures of both types of discrete sources as well as the extended emission are in a narrow range T_d=29-32K. The dust-to-gas ratio is 1.4x10^–4, uncertain by a factor of two. The far-infrared luminosity L_FIR=2.5x10⁷L_☉ of NGC 6822 is only 10% of the bolometric stellar luminosity. The ratio of the far-infrared to thermal radio continuum emission of the bright HII regions implies that the fraction of stellar photons absorbed by the dust is very similar to the fraction of Lyman continuum photons absorbed by the gas. A comparison of the nonthermal radio emission from NGC 6822 with its infrared emission suggests that previously found correlations between these quantities are not causal in nature. They appear to be critically dependent on the cosmic ray production rate and the degree of retention, which may vary, especially in dwarf galaxies. In NGC 6822, about half of the infrared emission orginates from dust heated by nonionizing stars. As it is thus not associated with recent star formation, it follows that far-infrared emission from galaxies by itself is not a good measure of recent star formation rates. In NGC 6822, recent star formation rates are dM/dt=0.04M_☉/yr and dM/(dt.dA)=0.04M_☉/yr/kpc² respectively. The global star formation efficiency is 3(+7,-2)%.