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摘要
The far-infrared (42.5-122.5-mu-m, hereafter FIR) and the 6.3 cm radio continuum map of the LMC are found closely correlated, in the sense of an overall coincidence of peaks in the two maps and a strong resemblence around giant star formation regions (30 Doradus, the bar, etc.). The FIR disk and the 6.3 cm disk have similar sizes. No gradient in the FIR-to-6.3cm brightness ratio with increasing galactic radius is found.
Statistical studies reveal that the local point-by-point correlation between the two maps is comparably strong as the global FIR/radio correlation for gas-rich galaxies. We do not find any dependence of the FIR-to-6.3 cm brightness ratio either on the FIR surface brightness or on the 6.3 cm surface brightness. Neither find we any evidence for a dependence of the FIR-to-6.3 cm brightness ratio on any other star formation indicator.
The FIR map is decomposed into warm and cool components, and the 6.3 cm map into the thermal and nonthermal components. It is found that 55% of FIR emission of the LMC is warm, and that 55% of 6.3 cm emission is thermal. The strong local FIR/6.3 cm correlation is dominated by the correlation between the warm FIR and the thermal radio emission, both of which are associated with young ionizing stars. The cool FIR and the nonthermal radio emissions exhibit more diverse local behaviours. On the other hand, the ratio between the integrated cool FIR flux and the integrated nonthermal 6.3 cm flux is equal to the ratio between the integrated warm FIR flux and the integrated thermal 6.3 cm flux, both following the global FIR/radio correlation very well, indicating that the contribution form the cool FIR/nonthermal radio correlation to the global FIR/radio correlation is equally important as that from the warm FIR/thermal radio correlation.
Dips of low FIR-to-6.3 cm brightness ratios (linear scale of approximately 70 pc) are found coincident with bright H II regions, indicating that the warm FIR emission is locally more extended than the thermal radio emission. The typical size of FIR emission regions around LMC star-formation regions is probably approximately 200 pc. The result suggests that the radiation from the dust associated with surrounding neutral gas heated by the non-ionizing UV radiation contributes significantly to the FIR luminosity of H II regions.
A systematic difference in the FIR-to-6.3 cm brightness ratio is found between the eastern and western half of the LMC, especially in the vicinity of giant star-formation regions. The asymmetry could be due to different ages of massive stars in the two halves, which give rise to different non-ioninzing-to-ionizing flux ratios. It could also be due to a difference in the gas-to-dust ratio in the two halves.
- 出版日期1992-4
- 单位CSIRO
